Here’s the paraphrased study-note version:

175. Toxicology – Odors as Diagnostic Clues

Definition

Certain toxic substances have characteristic odors that may provide a diagnostic clue during poisoning.

However, odor should never be used alone to identify a poison because:

• Odor perception varies greatly between individuals.
• Some people cannot detect particular odors.
• Several chemicals can produce similar smells.
• Multiple odors may mask one another.
• Olfactory fatigue can cause an odor to disappear even while the toxicant remains present.

Therefore:

Characteristic odor + exposure history + toxidrome + appropriate testing is much more useful than odor alone.

Olfactory Physiology

Most odors are detected by receptors located high within the nasal cavity.

Signals travel through:

Olfactory receptors → cranial nerve I → olfactory bulb → olfactory cortex/CNS

Some irritating chemicals also strongly stimulate the trigeminal nerve (cranial nerve V).

Examples include:

• Ammonia
• Other irritating vapors

This trigeminal stimulation contributes to sensations such as:

• Burning
• Stinging
• Irritation

Olfactory Fatigue

Olfactory fatigue is rapid adaptation to a persistent odor.

After continued exposure:

Odor initially detected → olfactory adaptation → odor becomes difficult or impossible to perceive

This is particularly dangerous with hydrogen sulfide.

A person may initially smell its characteristic rotten-egg odor and then stop noticing it despite continued exposure.

Therefore:

Loss of odor does NOT mean the environment is safe.

Important Odor Associations

Bitter Almond Odor

Classically associated with:

• Cyanide

However, the bitter-almond odor is an unreliable diagnostic sign because many people are genetically unable to detect it.

Cyanide should instead be suspected from:

• Compatible exposure
• Rapid neurologic deterioration
• Cardiovascular collapse
• Severe lactic acidosis

Rotten-Egg Odor

Important associations include:

• Hydrogen sulfide
• Sulfur-containing compounds
• Mercaptans

Hydrogen sulfide poisoning can cause:

• Eye and airway irritation
• Headache
• Dizziness
• Rapid CNS depression
• Seizures
• Respiratory failure
• Cardiovascular collapse

Hydrogen sulfide causes rapid olfactory fatigue, making smell especially unreliable as a safety warning.

Natural Gas Odor

Natural gas itself is normally given a warning odor by adding odorants such as mercaptans.

Therefore, the characteristic sulfur-like smell associated with household natural gas primarily reflects the added odorant rather than the fuel gas itself.

Garlic-Like Odor

Possible toxicologic associations include:

• Organophosphate pesticides
• Arsenic compounds
• Selenium
• Phosphorus
• Phosphine
• Tellurium

A garlic-like odor is not sufficiently specific to diagnose any of these exposures.

Associated clinical findings are much more useful.

Garlic Odor + Cholinergic Findings

Consider organophosphate poisoning when an exposure is accompanied by:

• Miosis
• Salivation
• Lacrimation
• Sweating
• Bronchorrhea
• Bronchospasm
• Vomiting
• Diarrhea
• Fasciculations
• Weakness

The cholinergic toxidrome is much more diagnostically important than odor.

Garlic or Fish-Like Odor + Severe Illness

Metal phosphides can release phosphine gas.

Potential exposures include:

• Aluminum phosphide
• Zinc phosphide
• Other metal phosphides

Severe poisoning can produce:

• Vomiting
• Abdominal pain
• Hypotension
• Metabolic acidosis
• Myocardial dysfunction
• Dysrhythmias
• Respiratory failure

A characteristic odor may occur but should not be relied upon for diagnosis.

Freshly Cut Hay or Musty Odor

Classically associated with:

• Phosgene

Phosgene exposure can initially cause relatively mild symptoms followed by delayed pulmonary injury.

Possible findings include:

• Cough
• Chest tightness
• Dyspnea
• Hypoxemia
• Pulmonary edema

A potentially dangerous feature is the delay between exposure and severe respiratory deterioration.

Chlorine/Bleach-Like Odor

Consider:

• Chlorine
• Other irritating halogen gases

Clinical effects may include:

• Eye irritation
• Burning throat
• Cough
• Chest tightness
• Bronchospasm
• Dyspnea

Severe exposure may cause acute lung injury and pulmonary edema.

Ammonia-Like Odor

Ammonia is a highly water-soluble respiratory irritant.

Exposure may produce:

• Eye pain
• Lacrimation
• Nasal and throat burning
• Cough
• Bronchospasm
• Upper-airway injury

High concentrations can produce severe airway and pulmonary injury.

An ammonia-like odor can also occur with uremia, although this is not a toxicant exposure.

Fruity or Acetone-Like Odor

Possible causes include:

• Acetone
• Isopropyl alcohol exposure
• Diabetic ketoacidosis
• Alcoholic ketoacidosis
• Some volatile solvents

Isopropyl alcohol is metabolized to acetone.

Typical isopropanol toxicity includes:

• CNS depression
• Nausea/vomiting
• Abdominal pain
• Hypotension in severe cases
• Ketosis

A major clue is:

Ketosis without the prominent high-anion-gap metabolic acidosis expected from ketoacidosis

Wintergreen Odor

A wintergreen or mint-like odor suggests:

• Methyl salicylate (oil of wintergreen)

Methyl salicylate poisoning produces the same systemic toxicity as other salicylates.

Possible findings include:

• Tachypnea
• Tinnitus
• Nausea/vomiting
• Diaphoresis
• Acid-base disturbances
• Altered mental status in severe poisoning

A serum salicylate concentration should be measured when clinically suspected.

Mothball Odor

Possible exposures include:

• Naphthalene
• Paradichlorobenzene
• Camphor-containing products

The clinical syndrome depends on the substance involved.

Naphthalene

Can cause:

• Oxidative hemolysis
• Methemoglobinemia
• Abdominal symptoms

Patients with G6PD deficiency are particularly susceptible to oxidative hemolysis.

Camphor

Significant ingestion may produce:

• Nausea/vomiting
• Agitation
• Seizures
• CNS toxicity

Therefore, identifying the actual moth-repellent ingredient is more important than recognizing the odor.

Paint or Solvent Odor

May suggest:

• Toluene
• Other volatile hydrocarbons/solvents

Toluene toxicity may cause:

• Euphoria followed by CNS depression
• Ataxia
• Confusion
• Weakness
• Hypokalemia
• Acid-base abnormalities

Chronic exposure may cause neurologic and renal abnormalities.

A paint odor on clothing or skin may support the exposure history but is not diagnostic.

Shoe-Polish-Like Odor

Historically associated with:

• Nitrobenzene
• Aniline compounds

These oxidizing chemicals can produce methemoglobinemia.

Clinical clues include:

• Cyanosis
• Dyspnea
• Headache
• Altered mental status
• Chocolate-brown blood
• Pulse oximetry that does not normalize appropriately with oxygen

Diagnosis requires co-oximetry.

Vinegar Odor

May suggest:

• Acetic acid

Concentrated acetic acid can cause corrosive injury.

Possible findings include:

• Oral or airway irritation
• Chest or abdominal pain
• Vomiting
• GI injury

Management should be based on the degree of corrosive exposure rather than the odor itself.

Tobacco Odor

May support exposure to:

• Nicotine-containing products

Significant nicotine toxicity can initially cause cholinergic-type stimulation with:

• Nausea
• Vomiting
• Abdominal pain
• Salivation
• Tachycardia
• Hypertension
• Tremor

Severe poisoning may progress to:

• Bradycardia
• Hypotension
• Weakness
• Seizures
• Respiratory failure

Odor + Clinical Findings

Odors become more useful when interpreted together with a toxidrome.

Examples:

Garlic odor + miosis + bronchorrhea + fasciculations

→ consider organophosphate poisoning

Rotten-egg odor + rapid CNS/cardiovascular collapse

→ consider hydrogen sulfide

Wintergreen odor + tachypnea + tinnitus + acid-base disturbance

→ consider methyl salicylate

Mothball odor + hemolysis/methemoglobinemia

→ consider naphthalene

Paint odor + CNS depression + hypokalemia

→ consider toluene

Fruity odor + CNS depression + ketosis

→ consider isopropanol/acetone

Bitter-almond odor + profound lactic acidosis/collapse

→ consider cyanide, while remembering that odor detection is unreliable

Laboratory Evaluation

Testing should be directed by the suspected toxicant and clinical presentation.

Possible investigations include:

• Electrolytes
• Glucose
• Bicarbonate
• BUN and creatinine
• Blood gas
• Lactate
• Serum osmolality
• Ketones
• ECG

Targeted testing may include:

• Salicylate concentration
• Co-oximetry
• Carboxyhemoglobin
• Methemoglobin
• Specific toxicant concentrations when clinically available

Lactate

Marked lactate elevation may occur with:

• Cyanide
• Hydrogen sulfide
• Carbon monoxide
• Severe hypoxia
• Shock
• Seizures

Lactate is therefore useful for assessing severity but is not specific for one poison.

Acid-Base Findings

A high-anion-gap metabolic acidosis may occur with several toxic exposures and other illnesses.

Examples include:

• Salicylate toxicity
• Cyanide
• Severe carbon monoxide poisoning
• Hydrogen sulfide poisoning
• Shock
• Seizures
• Diabetic ketoacidosis

Toluene can produce hypokalemia with a normal-anion-gap metabolic acidosis, although acid-base findings vary depending on timing and exposure.

Chest Imaging

Chest radiography may be appropriate after significant inhalational exposure when there is:

• Dyspnea
• Hypoxemia
• Abnormal lung examination
• Persistent respiratory symptoms

Pulmonary infiltrates or edema may develop after severe exposure to:

• Chlorine
• Ammonia
• Phosgene
• Phosphine
• Other severe inhalational irritants

Some pulmonary injuries can be delayed, so an initially normal chest radiograph does not always exclude significant exposure.

Management

Management is based on the suspected toxicant and clinical syndrome, not the odor itself.

General priorities include:

• Remove the patient from ongoing exposure.
• Protect rescuers and healthcare personnel from secondary exposure.
• Stabilize airway, breathing, and circulation.
• Provide oxygen when indicated.
• Treat seizures and dysrhythmias.
• Correct important electrolyte and acid-base abnormalities.
• Use a specific antidote when indicated for the identified or strongly suspected poison.

Decontamination

Inhalational Exposure

Remove the patient from the contaminated environment.

Rescuers should not enter a hazardous atmosphere without appropriate protective equipment.

Dermal Exposure

When clinically appropriate:

• Remove contaminated clothing.
• Irrigate exposed skin thoroughly.

Ingestion

Gastrointestinal decontamination depends on:

• Specific toxicant
• Timing
• Amount
• Clinical condition
• Airway status

Do not induce vomiting.

Routine gastric lavage is not recommended.

Important Diagnostic Pitfalls

No Odor Does Not Exclude Poisoning

A dangerous toxicant may:

• Have little or no odor
• Be present below the person’s odor threshold
• Be masked by another smell
• Be undetectable because the person has impaired olfaction

Therefore, absence of smell provides no reliable reassurance.

Odor Disappearance Does Not Mean Safety

This is particularly important with hydrogen sulfide.

Olfactory fatigue → smell disappears while toxic exposure continues

Never use the ability to smell a gas as a measure of environmental safety.

Odor Is Not Proof of Toxicity

Some substances can be smelled at concentrations far below those producing toxicity.

Conversely, some dangerous exposures can occur without a noticeable odor.

Key Points

• Characteristic odors can provide a supporting diagnostic clue, but they rarely identify a poison reliably by themselves.
• Most odor perception occurs through cranial nerve I, while irritating vapors can also stimulate cranial nerve V.
• Olfactory fatigue can make an odor disappear despite continued exposure.
• Hydrogen sulfide is the classic example where relying on smell can be especially dangerous.
• Bitter almond → cyanide, but many people cannot detect this odor.
• Rotten eggs → hydrogen sulfide, although sulfur compounds and odorants can smell similar.
• Garlic-like odor → organophosphates, phosphine, arsenic, selenium, or other compounds, but it is nonspecific.
• Fresh hay/musty odor → phosgene is a classic association.
• Wintergreen → methyl salicylate.
• Mothballs → naphthalene, paradichlorobenzene, or camphor.
• Paint/solvent odor → consider toluene or another volatile solvent.
• Fruity/acetone odor → consider ketosis, acetone, or isopropanol exposure.
• Always combine odor with the exposure history, physical findings, toxidrome, and targeted laboratory testing.
• Never assume an environment is safe simply because a toxic odor is no longer detectable.

Toxicology – Neuroleptic Malignant Syndrome (NMS) and Serotonin Syndrome (SS)

Definition

Neuroleptic malignant syndrome (NMS) and serotonin syndrome (SS) are potentially life-threatening hyperthermic syndromes associated with medications.

Both can cause:

• Altered mental status
• Hyperthermia
• Autonomic instability
• Abnormal muscle activity
• Rhabdomyolysis in severe cases

The major distinction is:

• NMS → dopamine blockade or withdrawal of dopaminergic therapy
• SS → excessive serotonergic activity

Their neuromuscular findings and speed of onset are particularly useful for distinguishing them.

Neuroleptic Malignant Syndrome (NMS)

NMS is primarily associated with reduced central dopaminergic activity.

Common Causes

NMS may occur after:

• Starting a dopamine antagonist
• Increasing the dose of an antipsychotic
• Using a potent dopamine-blocking medication
• Rapid dose escalation
• Abruptly stopping a dopaminergic medication

Important causative drugs include:

• Antipsychotics
• Metoclopramide
• Prochlorperazine
• Other dopamine receptor antagonists

NMS can also occur after abrupt withdrawal of drugs used to increase dopamine activity, such as levodopa.

Pathophysiology of NMS

Central dopamine receptor blockade, particularly involving D₂ receptors, interferes with:

• Hypothalamic thermoregulation
• Basal ganglia motor control
• Autonomic function

This can produce:

Dopamine blockade → severe rigidity + autonomic instability + hyperthermia + altered mental status

Severe muscle rigidity generates substantial heat and may cause extensive skeletal-muscle breakdown.

Clinical Features of NMS

The classic features are:

• Hyperthermia
• Altered mental status
• Severe generalized muscle rigidity
• Autonomic instability

Mental-status abnormalities include:

• Agitation
• Confusion
• Delirium
• Mutism
• Stupor
• Coma

Autonomic findings include:

• Tachycardia
• Hypertension
• Hypotension
• Diaphoresis
• Tachypnea
• Dysrhythmias

Muscular Findings in NMS

The characteristic finding is severe generalized “lead-pipe” rigidity.

Other extrapyramidal abnormalities may include:

• Tremor
• Bradykinesia
• Cogwheel rigidity
• Dystonia

The severe sustained muscle activity can produce:

• Elevated creatine kinase (CK)
• Rhabdomyolysis
• Hyperkalemia
• Acute kidney injury
• Hyperthermia

Laboratory Findings in NMS

Common abnormalities include:

• Markedly elevated CK
• Leukocytosis
• Elevated AST/ALT
• Metabolic acidosis
• Electrolyte abnormalities
• Myoglobinuria
• Acute kidney injury

CK elevation supports the diagnosis but is not specific for NMS.

The diagnosis remains primarily clinical.

Serotonin Syndrome

Serotonin syndrome results from excessive serotonergic activity in the CNS and peripheral nervous system.

It is usually associated with:

• Starting a serotonergic drug
• Increasing its dose
• Overdose
• Combining serotonergic medications
• Drug interactions that increase serotonin activity

Important Serotonergic Drugs

Potential causes include:

• SSRIs
• SNRIs
• MAO inhibitors
• Some tricyclic antidepressants
• Tramadol
• Dextromethorphan
• Linezolid
• Lithium
• Certain opioids with serotonergic activity
• Other serotonin-enhancing medications

The greatest risk often occurs when multiple serotonergic mechanisms are combined, especially combinations involving an MAO inhibitor.

Pathophysiology of Serotonin Syndrome

Excessive stimulation of serotonin receptors, particularly 5-HT₁A and 5-HT₂A receptors, produces the syndrome.

The characteristic clinical pattern consists of:

Mental-status changes + autonomic hyperactivity + neuromuscular hyperactivity

Mental-Status Findings in SS

Possible findings include:

• Anxiety
• Restlessness
• Agitation
• Confusion
• Delirium

Severe cases may produce:

• Seizures
• Coma

Autonomic Findings in SS

Common manifestations include:

• Diaphoresis
• Tachycardia
• Hypertension
• Hyperthermia
• Dilated pupils
• Increased bowel activity
• Diarrhea

Blood pressure can become unstable in severe cases.

Neuromuscular Findings in SS

The most important findings are:

• Clonus
• Hyperreflexia
• Tremor
• Myoclonus
• Increased muscle tone

Clonus may be:

• Spontaneous
• Inducible
• Ocular

Hyperreflexia and clonus are often particularly prominent in the lower extremities.

These findings are among the most useful clues distinguishing serotonin syndrome from NMS.

Hunter Serotonin Toxicity Criteria

Modern diagnosis commonly uses the Hunter Serotonin Toxicity Criteria rather than the older nonspecific criteria in the source.

In a patient with serotonergic exposure, serotonin toxicity is strongly supported by characteristic combinations involving:

• Spontaneous clonus
• Inducible clonus with agitation or diaphoresis
• Ocular clonus with agitation or diaphoresis
• Tremor with hyperreflexia
• Hypertonia with elevated temperature plus ocular or inducible clonus

The emphasis is therefore on clonus and hyperreflexia rather than nonspecific findings such as tachycardia alone.

Distinguishing NMS from Serotonin Syndrome

NMS

Think:

Dopamine blockade → slow onset → severe rigidity

Typical clues:

• Dopamine antagonist exposure
• Withdrawal of dopaminergic therapy
• Usually develops over days
• Severe generalized lead-pipe rigidity
• Bradykinesia
• Reflexes often normal or reduced
• Markedly elevated CK may occur
• GI hyperactivity is not characteristic

Serotonin Syndrome

Think:

Serotonin excess → rapid onset → clonus and hyperreflexia

Typical clues:

• Serotonergic medication exposure or interaction
• Usually develops within hours
• Hyperreflexia
• Clonus
• Tremor
• Myoclonus
• Diaphoresis
• Increased bowel sounds
• Diarrhea

High-Yield Distinction

NMS = rigidity + bradykinesia

SS = clonus + hyperreflexia

Onset

NMS

NMS generally develops more gradually.

Symptoms commonly evolve over approximately 1–3 days, although timing varies.

Serotonin Syndrome

Serotonin syndrome usually develops rapidly, often within hours of:

• Starting a serotonergic drug
• Increasing a dose
• Overdose
• Adding an interacting drug

Rapid onset strongly supports serotonin syndrome over NMS when the clinical findings are otherwise similar.

Hyperthermia

Both syndromes can cause dangerous hyperthermia.

The temperature elevation is largely generated by excessive skeletal-muscle activity, particularly in severe disease.

Complications include:

• Rhabdomyolysis
• Hyperkalemia
• Metabolic acidosis
• Acute kidney injury
• DIC
• Hepatic injury
• Cardiovascular collapse
• Multiorgan failure

Severe hyperthermia requires immediate treatment.

Differential Diagnosis

Other conditions that can resemble NMS or serotonin syndrome include:

• Malignant hyperthermia
• Sympathomimetic toxicity
• Anticholinergic syndrome
• MAOI toxicity
• Alcohol or sedative-hypnotic withdrawal
• Heat stroke
• Sepsis
• Meningitis/encephalitis
• Thyroid storm
• Severe agitation
• Status epilepticus
• Catatonia

The medication history and neuromuscular examination are especially important.

Malignant Hyperthermia

Malignant hyperthermia is usually triggered during anesthesia by:

• Certain volatile anesthetic agents
• Succinylcholine

Features include:

• Rapidly increasing CO₂ production
• Muscle rigidity
• Acidosis
• Hyperkalemia
• Rhabdomyolysis
• Hyperthermia

Dantrolene is the specific treatment for malignant hyperthermia.

It should not be confused with NMS merely because both conditions can involve rigidity and hyperthermia.

Sympathomimetic Toxicity

Stimulant poisoning can cause:

• Agitation
• Tachycardia
• Hypertension
• Mydriasis
• Diaphoresis
• Hyperthermia
• Tremor
• Seizures

However, the characteristic clonus and marked hyperreflexia of serotonin syndrome are generally absent.

Anticholinergic Syndrome

Anticholinergic toxicity can cause:

• Hyperthermia
• Agitated delirium
• Tachycardia
• Mydriasis

A useful clue is:

Anticholinergic → hot and dry

whereas serotonin syndrome commonly produces diaphoresis and increased bowel activity.

Diagnostic Evaluation

There is no single laboratory test that confirms either NMS or serotonin syndrome.

Evaluation should include:

• Detailed medication history
• Recent dose changes
• Drug interactions
• Neurologic examination
• Reflex examination
• Assessment for clonus
• Core temperature
• Hydration and perfusion status

Laboratory Tests

Important investigations in significant cases include:

• CK
• Electrolytes
• Glucose
• Renal function
• Liver enzymes
• CBC
• Blood gas when indicated
• Lactate
• Urinalysis
• ECG

Urinalysis may show evidence of myoglobinuria from rhabdomyolysis.

Other tests should be directed toward alternative diagnoses when necessary.

Management of Both Syndromes

Initial management includes:

• Stop the causative medication.
• Stabilize airway and breathing.
• Establish IV access.
• Begin cardiac monitoring.
• Monitor core temperature.
• Correct dehydration and electrolyte abnormalities.
• Control agitation.
• Treat seizures.
• Actively cool significant hyperthermia.

Severe cases require intensive monitoring.

Benzodiazepines

Benzodiazepines are particularly useful for:

• Agitation
• Tremor
• Seizures
• Excessive muscle activity

They can also decrease heat generation by reducing agitation and muscular activity.

They are especially important in serotonin syndrome.

Cooling

Hyperthermia should be treated with physical cooling, such as:

• Evaporative cooling
• Fans
• Other active external cooling measures

Antipyretics such as acetaminophen are generally ineffective because the temperature elevation is not caused by an increased hypothalamic set point.

Severe Hyperthermia

Extreme hyperthermia caused by sustained muscle activity may require:

• Deep sedation
• Endotracheal intubation
• Mechanical ventilation
• Neuromuscular paralysis

A nondepolarizing neuromuscular blocker is generally preferred when paralysis is required.

Rapid control of muscle activity is essential because continued rigidity can generate enormous amounts of heat.

Treatment of NMS

The most important intervention is:

Immediately stop the dopamine-blocking medication.

Supportive treatment includes:

• IV fluids when appropriate
• Cooling
• Correction of electrolyte abnormalities
• Treatment of rhabdomyolysis
• Management of renal complications
• Benzodiazepines

Most treatment is fundamentally supportive.

Dantrolene in NMS

Dantrolene reduces skeletal-muscle contraction and may be considered in selected severe NMS cases.

Evidence for its benefit in NMS is less established than for malignant hyperthermia.

It should therefore be regarded as an adjunct in selected severe cases, not a universal antidote for NMS.

Bromocriptine in NMS

Bromocriptine is a dopamine agonist that may be considered in selected moderate-to-severe NMS cases.

Other dopaminergic strategies may occasionally be used under specialist guidance.

Again, supportive care and removal of the offending drug remain central.

Treatment of Serotonin Syndrome

The first step is:

Stop all serotonergic medications.

Most mild-to-moderate cases improve with:

• Discontinuation of serotonergic drugs
• Benzodiazepines
• IV fluids when required
• Cooling
• Supportive care

Because many serotonergic drugs have relatively short effective durations, improvement can occur relatively quickly once the responsible agents are stopped.

Cyproheptadine

Cyproheptadine is a serotonin antagonist that may be considered in moderate or severe serotonin syndrome when supportive treatment and benzodiazepines are insufficient.

It is administered enterally rather than intravenously.

Evidence is largely based on clinical experience rather than high-quality randomized trials.

Blood Pressure Abnormalities

Both syndromes may produce:

• Hypertension
• Hypotension
• Rapid blood-pressure fluctuations

Hypertension often improves when:

• Agitation is controlled
• Rigidity decreases
• Hyperthermia is treated

Persistent severe abnormalities should be treated with short-acting, titratable agents appropriate to the patient’s hemodynamic state.

The source’s routine dopamine-first approach for hypotension is outdated; vasopressor choice should reflect the mechanism and current critical-care practice.

Rhabdomyolysis

Severe rigidity and hyperthermia can produce extensive skeletal-muscle breakdown.

Monitor:

• CK
• Potassium
• Creatinine
• Urine output
• Acid-base status

Complications include:

• Hyperkalemia
• Acute kidney injury
• Dysrhythmias

Decontamination

Do not induce vomiting.

Routine gastric lavage is not recommended.

Activated charcoal may be considered only after selected recent ingestions when:

• The drug is adsorbed by charcoal,
• Clinically significant toxicity is expected, and
• The airway can be safely protected.

Decontamination must never delay treatment of hyperthermia, seizures, rigidity, or cardiovascular instability.

Monitoring

Severe NMS or serotonin syndrome requires close monitoring of:

• Core temperature
• Mental status
• Cardiac rhythm
• Blood pressure
• Respiratory function
• CK
• Electrolytes
• Renal function
• Urine output

Patients with severe hyperthermia, rigidity, cardiovascular instability, seizures, or organ dysfunction generally require intensive-care management.

Expected Course

NMS

NMS generally:

• Develops more slowly
• Lasts longer
• May take days to resolve after the responsible drug is discontinued

Long-acting or depot antipsychotic exposure may prolong the syndrome.

Serotonin Syndrome

Serotonin syndrome generally:

• Begins rapidly
• Improves more rapidly after serotonergic drugs are stopped

Many uncomplicated cases improve substantially within about a day, although toxicity from long-acting agents or active metabolites can persist longer.

Key Points

• NMS and serotonin syndrome can both cause hyperthermia, altered mental status, autonomic instability, and abnormal muscle activity.
• NMS is associated with dopamine blockade or withdrawal of dopaminergic therapy.
• Serotonin syndrome results from excessive serotonergic activity.
• NMS generally has a slower onset with severe generalized rigidity and bradykinesia.
• Serotonin syndrome generally has a rapid onset with hyperreflexia and clonus.
• Clonus is one of the most useful findings suggesting serotonin syndrome.
• Diarrhea and increased bowel activity favor serotonin syndrome.
• Marked CK elevation and severe sustained rigidity are particularly characteristic of NMS, although they are not exclusive to it.
• The Hunter Serotonin Toxicity Criteria are commonly used to diagnose serotonin toxicity.
• Both syndromes can cause rhabdomyolysis, hyperkalemia, AKI, dysrhythmias, and multiorgan failure.
• Stop the causative medication immediately.
• Benzodiazepines, supportive care, and aggressive temperature control are central treatments.
• Cyproheptadine may be considered for significant serotonin syndrome.
• Dantrolene or bromocriptine may be considered in selected severe NMS cases.
• Antipyretics generally do not correct the hyperthermia because excessive muscle activity—not a raised hypothalamic set point—is the primary problem.
• Severe hyperthermia requires rapid control because prolonged extreme temperature can itself cause life-threatening organ injury.

Toxicology – Multiple Chemical Sensitivity (MCS)

Definition

Multiple chemical sensitivity (MCS) describes a syndrome in which a person reports recurrent symptoms involving multiple organ systems after exposure to low concentrations of various environmental chemicals.

The term is controversial because these exposures are typically below concentrations expected to cause direct toxic effects, and no specific toxicologic mechanism or diagnostic biomarker has been established.

The term idiopathic environmental intolerance (IEI) is also commonly used because it describes the clinical phenomenon without assuming that chemical toxicity is the underlying mechanism.

Typical Pattern

Features traditionally associated with MCS/IEI include:

• Symptoms beginning after a perceived environmental or occupational exposure
• Symptoms involving several organ systems
• Recurrence with particular environmental triggers
• Symptoms attributed to chemically unrelated substances
• Reactions occurring at concentrations below established toxic thresholds
• Improvement after leaving the triggering environment

Frequently reported triggers include:

• Perfumes and fragrances
• Cleaning products
• Solvents
• Pesticides
• Vehicle exhaust
• Paints
• Smoke
• Other strongly scented or irritating substances

Pathophysiology

There is no established single pathophysiologic mechanism that explains MCS/IEI.

Proposed mechanisms have included:

• Altered sensory processing
• Neurobiologic mechanisms
• Autonomic responses
• Stress-response pathways
• Conditioning or learned responses
• Psychological and psychophysiologic mechanisms
• Immunologic mechanisms

However, a reproducible pattern of:

• Immune dysfunction
• Toxicant accumulation
• Specific biochemical abnormalities
• Organ injury

has not been demonstrated consistently enough to serve as a diagnostic explanation.

Important Clinical Principle

The absence of a demonstrated toxicologic mechanism does not mean that the patient’s symptoms are fabricated.

Symptoms can be genuine and functionally significant even when conventional examination and laboratory testing do not identify a specific toxic injury.

The clinical task is therefore to:

Validate the symptoms → investigate plausible medical/toxicologic causes → avoid unsupported causal conclusions → provide evidence-based symptom management

Epidemiology

The exact prevalence depends heavily on how MCS/IEI is defined.

Historically, many clinical series have reported a predominance of women.

Symptoms may be mild in some patients but can substantially interfere with:

• Employment
• Social activities
• Travel
• Use of public spaces
• Daily functioning

Triggering Events

Some patients describe onset after:

• Occupational chemical exposure
• Irritant-gas exposure
• Solvent exposure
• Pesticide exposure
• Building-related exposure
• Other environmental events

Later, symptoms may be attributed to much smaller exposures and to substances chemically unrelated to the original trigger.

A reported initiating exposure should be evaluated on its own merits rather than automatically assumed to have caused chronic systemic toxicity.

Clinical Features

Symptoms are usually nonspecific and multisystemic.

Common complaints include:

Neurologic/general

• Headache
• Fatigue
• Difficulty concentrating
• Subjective memory problems
• Dizziness
• Weakness
• Tremor
• Paresthesias
• Sleep disturbance

Respiratory/ENT

• Nasal irritation or congestion
• Throat discomfort
• Cough
• Dyspnea
• Chest tightness
• Sensitivity to odors

Cardiovascular

• Palpitations
• Chest discomfort

Gastrointestinal

• Nausea
• Abdominal discomfort
• Appetite changes
• Altered bowel habits

Dermatologic

• Pruritus
• Rash
• Dryness

Psychological symptoms such as anxiety or low mood may coexist, but their presence does not by itself establish the cause of the overall syndrome.

Physical Examination

There is no characteristic physical finding that confirms MCS/IEI.

The examination is instead important for detecting alternative explanations.

Particular attention should be given to:

• Neurologic abnormalities
• Respiratory disease
• Dermatologic findings
• Cardiovascular abnormalities
• Thyroid findings
• Signs of systemic inflammatory disease
• Objective evidence of a specific toxic exposure

Differential Diagnosis

Before attributing symptoms to MCS/IEI, consider established medical disorders capable of producing similar complaints.

Examples include:

• Asthma
• Allergic rhinitis
• Migraine
• Thyroid disease
• Anemia
• Sleep disorders
• Autoimmune/inflammatory disease
• Neurologic disease
• Medication adverse effects
• Anxiety or panic disorders
• Depression
• Other causes of chronic fatigue or cognitive symptoms

A genuine occupational or environmental exposure should also be investigated when the history supports one.

Specific Toxic Exposures

Potential exposures sometimes attributed to MCS include:

• Heavy metals
• Solvents
• Pesticides
• Formaldehyde
• Irritant gases

These should not be diagnosed merely from nonspecific symptoms.

A specific poisoning diagnosis requires a plausible combination of:

Exposure history + dose/intensity + timing + expected clinical syndrome ± appropriate objective testing

Diagnostic Approach

There is currently no single laboratory test, imaging study, allergy test, or biomarker that establishes MCS/IEI.

Evaluation begins with a detailed history covering:

• Initial triggering event
• Specific suspected substances
• Exposure route
• Duration and intensity
• Temporal relationship between exposure and symptoms
• Occupational environment
• Medication history
• Medical history
• Pattern of symptom recurrence
• Functional impact

Laboratory Testing

Testing should be targeted to the clinical presentation, rather than applying a large universal panel to every patient.

Depending on symptoms, reasonable evaluation may include:

• CBC
• Electrolytes
• Glucose
• Renal function
• Liver tests
• Thyroid studies

Additional investigations should be guided by specific clinical findings.

Heavy-Metal Testing

Heavy-metal testing should be performed when there is a credible exposure history or compatible clinical syndrome.

Indiscriminate screening can produce misleading results because detectable amounts of many metals may occur without clinical poisoning.

Provoked urine metal testing after administration of a chelator is not an accepted method for diagnosing chronic heavy-metal poisoning.

Allergy and Immune Testing

MCS/IEI should not automatically be interpreted as an allergic disorder.

Conventional allergy evaluation is appropriate when symptoms suggest:

• Asthma
• Allergic rhinitis
• Urticaria
• Anaphylaxis
• Another established hypersensitivity disorder

Broad unconventional immune panels have not been shown to diagnose MCS reliably.

Treatment

There is no specific antidote or universally established pharmacologic treatment for MCS/IEI.

Management should focus on:

• Identifying and treating established medical conditions
• Managing individual symptoms
• Maintaining daily function
• Addressing occupational concerns
• Avoiding unnecessary medications or procedures
• Providing consistent longitudinal medical care

Exposure Reduction

Avoiding a substance that causes documented irritation, allergy, or toxicity is appropriate.

However, increasingly restrictive avoidance of extremely low-level everyday environmental exposures can sometimes lead to:

• Social isolation
• Occupational disability
• Reduced physical activity
• Increasing sensitivity or fear surrounding ordinary environments

Management should therefore balance reasonable exposure reduction with preservation of normal function.

Psychological and Behavioral Treatment

When symptoms are associated with anxiety, conditioned responses, stress, or significant functional impairment, interventions such as:

• Cognitive behavioral approaches
• Stress-management strategies
• Treatment of anxiety or depression when present
• Gradual rehabilitation

may be useful.

These interventions should be presented as methods for reducing symptoms and improving function, not as evidence that symptoms are imaginary.

Occupational Management

When symptoms occur at work, an occupational and environmental medicine evaluation can help determine:

• What substances are actually present
• Whether concentrations are potentially hazardous
• Whether coworkers are affected
• Whether ventilation is adequate
• Whether exposure controls are indicated

Objective exposure assessment is preferable to assuming either that the workplace is toxic or that the exposure is irrelevant.

Treatments to Avoid

Without evidence of a specific indication, avoid:

• Empiric chelation
• Unvalidated “detoxification” regimens
• Extreme elimination diets
• Unsupported immune therapies
• Repeated unnecessary laboratory panels
• Unvalidated chemical-provocation testing
• Excessively restrictive environmental avoidance

These approaches may cause direct harm, reinforce disability, or delay diagnosis of another medical disorder.

Acute Exposure

If a patient with a history of MCS presents after a new substantial chemical exposure, that event should be evaluated as a possible acute poisoning on its own merits.

Do not assume that new symptoms are simply part of MCS.

Conversely, the presence of symptoms after detecting an odor does not by itself establish toxic exposure.

Decontamination

There is no routine decontamination procedure for MCS/IEI.

Decontamination is appropriate only when there has been a specific acute exposure requiring it.

Gastric decontamination has no role merely because chronic symptoms are attributed to environmental chemicals.

Prognosis

The course is variable.

Symptoms may:

• Resolve
• Fluctuate
• Recur with perceived triggers
• Persist chronically

For some patients, functional impairment becomes more significant than measurable physiologic abnormalities.

A stable therapeutic relationship and emphasis on function, symptom control, and appropriate investigation are important.

Key Points

• MCS describes recurrent multisystem symptoms attributed to low-level exposure to multiple chemically unrelated substances.
• Idiopathic environmental intolerance (IEI) is a commonly used alternative term that avoids assuming a proven toxic mechanism.
• No reproducible biochemical, immunologic, or toxicologic abnormality has been established as a universal explanation.
• There is no diagnostic biomarker or specific antidote.
• Symptoms can be genuine and disabling even when objective evidence of toxic injury is absent.
• Do not automatically attribute symptoms either to chemical toxicity or to psychiatric disease.
• Specific poisoning requires a credible exposure history, appropriate timing, compatible clinical findings, and targeted testing when available.
• Laboratory testing should be guided by the presentation rather than broad indiscriminate screening.
• Provoked urine heavy-metal testing and empiric chelation are not appropriate diagnostic or therapeutic approaches.
• Treat identifiable medical disorders and individual symptoms while supporting normal function.
• Reasonable exposure control is appropriate, but extreme avoidance of ordinary low-level environmental exposures can itself become functionally harmful.
• A new significant exposure should always be evaluated independently rather than automatically attributed to the pre-existing MCS/IEI label.

Toxicology – Movement Disorders

Definition

Abnormal movements can provide important clues to the cause of poisoning or medication toxicity.

Toxicologic movement disorders include:

• Akathisia
• Asterixis
• Myoclonus
• Ataxia
• Chorea
• Dystonia
• Dysarthria
• Fasciculations
• Nystagmus
• Drug-induced parkinsonism
• Rigidity
• Tremor
• Tardive dyskinesia

Recognition of the movement pattern + medication/exposure history + associated toxidrome is usually more useful than the movement abnormality alone.

Akathisia

Akathisia is a subjective feeling of inner restlessness accompanied by an inability to remain still.

Patients may:

• Pace
• Rock back and forth
• Repeatedly cross and uncross their legs
• Constantly shift position
• Report intense internal restlessness

It may be mistaken for anxiety, agitation, or worsening psychiatric illness.

Common drug causes include:

• Antipsychotics
• Metoclopramide and other dopamine-antagonist antiemetics
• Some antidepressants
• Other dopamine-blocking drugs

Symptoms often follow initiation or an increase in dose.

Asterixis

Asterixis is a negative myoclonus caused by brief interruptions of sustained muscle contraction.

When the arms and wrists are extended, there are intermittent lapses of posture producing the characteristic “flapping” movement.

Toxicologic causes include:

• Sedative-hypnotics
• Anticonvulsants
• Some psychoactive medications

Important nontoxic causes include:

• Hepatic encephalopathy
• Uremia
• Hypercapnia
• Other metabolic encephalopathies

Myoclonus

Myoclonus consists of brief, sudden, shock-like involuntary movements.

Unlike asterixis, classic positive myoclonus results from sudden muscle contraction.

Drug-related causes include:

• Serotonergic medications
• Opioids
• Anticonvulsants
• Lithium
• Some antidepressants
• Sedative-hypnotics

Myoclonus accompanied by hyperreflexia and clonus should raise concern for serotonin toxicity.

Ataxia

Ataxia is impaired coordination of voluntary movement.

Manifestations include:

• Unsteady gait
• Difficulty standing
• Poor limb coordination
• Dysmetria
• Impaired balance

Common toxicologic causes include:

• Ethanol
• Benzodiazepines
• Barbiturates
• Anticonvulsants
• Lithium
• Sedating antihistamines
• Other CNS depressants

Phenytoin and Ataxia

Phenytoin toxicity classically produces a progression of neurologic abnormalities such as:

• Nystagmus
• Ataxia
• Dysarthria
• Tremor
• Increasing CNS depression at higher exposure

These findings can be particularly useful when correlated with the clinical history and serum phenytoin concentration.

Chorea

Chorea consists of irregular, unpredictable, nonrhythmic movements that seem to flow randomly from one body region to another.

Very forceful choreiform movements are sometimes termed ballism.

Toxic or medication-related causes include:

• Dopaminergic medications
• Stimulants
• Antipsychotic-related movement disorders
• Lithium
• Carbon monoxide
• Manganese
• Some anticonvulsants

Metabolic causes include:

• Hypoglycemia or hyperglycemia
• Sodium abnormalities
• Calcium abnormalities
• Hyperthyroidism

Neurologic alternatives include Huntington disease and Wilson disease.

Dystonia

Dystonia consists of sustained or intermittent muscle contractions producing abnormal movements or postures.

Acute drug-induced dystonia commonly affects the:

• Face
• Eyes
• Jaw
• Tongue
• Neck

Manifestations include:

• Oculogyric crisis – forced upward or lateral eye deviation
• Torticollis – abnormal neck turning
• Retrocollis – backward neck extension
• Jaw spasm
• Tongue protrusion
• Blepharospasm
• Dysarthria
• Dysphagia
• Opisthotonic posturing

Acute Dystonic Reaction

The classic causes are dopamine D₂-receptor antagonists, especially:

• Antipsychotics
• Metoclopramide
• Prochlorperazine
• Other dopamine-blocking antiemetics

Acute dystonia can be dramatic and frightening but usually responds rapidly to an anticholinergic medication such as diphenhydramine or benztropine.

Rare laryngeal dystonia can compromise the airway and requires urgent treatment.

Dysarthria

Dysarthria is impaired articulation caused by poor motor control of the muscles involved in speech.

Speech may become:

• Slurred
• Slow
• Poorly articulated

Toxic causes include:

• Ethanol
• Sedative-hypnotics
• Anticonvulsants
• Lithium
• Other CNS-depressant drugs

Dysarthria often accompanies ataxia and nystagmus in sedative or anticonvulsant toxicity.

Fasciculations

Fasciculations are visible, brief contractions of individual motor units.

Important toxicologic causes include:

• Organophosphates
• Carbamates
• Nicotine
• Some stimulants
• Certain neurotoxins

In organophosphate poisoning, fasciculations represent nicotinic acetylcholine receptor overstimulation and may progress to:

• Muscle weakness
• Paralysis
• Respiratory failure

When accompanied by miosis, bronchorrhea, salivation, sweating, and diarrhea, a cholinergic syndrome should be strongly suspected.

Nystagmus

Nystagmus is rhythmic involuntary movement of the eyes.

Toxicologic causes include:

• Sedative-hypnotics
• Anticonvulsants
• Lithium
• Phencyclidine (PCP)
• Ethanol

The direction and pattern can sometimes provide additional clues.

PCP and Nystagmus

PCP intoxication is classically associated with:

• Horizontal, vertical, or rotatory nystagmus
• Agitation or unusual behavior
• Analgesia
• Hypertension
• Tachycardia
• Ataxia

Vertical nystagmus in an intoxicated patient is an especially useful clue, although it is not completely specific.

Parkinsonism

Drug-induced parkinsonism resembles Parkinson disease and may produce:

• Bradykinesia
• Rigidity
• Tremor
• Shuffling gait
• Reduced facial expression
• Postural instability

The major medication mechanism is dopamine D₂ receptor blockade.

Common causes include:

• Antipsychotics
• Metoclopramide
• Prochlorperazine
• Other dopamine antagonists

Toxic Parkinsonism

Toxic exposures associated with parkinsonian syndromes include:

• Manganese
• Carbon monoxide
• Methanol
• Carbon disulfide
• MPTP

MPTP is particularly notable because its toxic metabolite selectively damages dopaminergic neurons in the substantia nigra and can produce profound parkinsonism.

Rigidity

Rigidity is increased resistance to passive movement.

In toxicology, marked rigidity accompanied by hyperthermia and altered mental status should immediately raise concern for:

• Neuroleptic malignant syndrome
• Serotonin syndrome
• Malignant hyperthermia
• Severe MAOI toxicity

The accompanying neuromuscular findings help differentiate them.

NMS vs. Serotonin Syndrome

Neuroleptic malignant syndrome

• Dopamine blockade or withdrawal of dopaminergic therapy
• Usually slower onset
• Severe generalized rigidity
• Hyporeflexia or relatively normal reflexes
• Hyperthermia
• Autonomic instability
• Altered mental status
• Elevated CK

Serotonin syndrome

• Serotonergic exposure
• Usually rapid onset
• Hyperreflexia
• Clonus
• Tremor
• Agitation
• Diaphoresis
• Hyperthermia
• GI hyperactivity may occur

The presence of clonus strongly favors serotonin toxicity.

Tremor

Tremor is a rhythmic oscillating movement.

It may be classified as:

• Resting
• Postural
• Kinetic/action

Important toxicologic causes include:

• Lithium
• Valproate
• Stimulants
• Caffeine
• Beta₂-adrenergic agonists
• Theophylline
• Thyroid hormone excess
• Heavy metals
• Alcohol or sedative withdrawal

The pattern of tremor alone rarely identifies the toxicant, so associated findings are essential.

Lithium

Lithium toxicity can produce multiple movement abnormalities, including:

• Coarse tremor
• Ataxia
• Dysarthria
• Myoclonus
• Fasciculations
• Nystagmus
• Chorea in severe cases

Progressive neurologic abnormalities in a patient taking lithium should prompt assessment for toxicity.

Tardive Dyskinesia

Tardive dyskinesia is a delayed hyperkinetic movement disorder associated primarily with prolonged exposure to dopamine receptor-blocking medications.

Typical manifestations include:

• Lip smacking
• Chewing movements
• Grimacing
• Tongue protrusion
• Repetitive facial movements
• Limb or trunk movements

Unlike acute dystonia, tardive dyskinesia usually develops after chronic exposure.

Symptoms can persist after the responsible medication is discontinued.

Tardive Dystonia

Tardive dystonia is another delayed complication of chronic dopamine receptor blockade.

It causes sustained abnormal postures and may involve:

• Neck
• Trunk
• Limbs
• Cranial muscles

It should be distinguished from an acute dystonic reaction, which generally appears shortly after beginning or increasing a dopamine-blocking medication.

Extrapyramidal Syndromes

A useful framework for dopamine-blocking medication effects is:

Hours to days

→ acute dystonia

Days to weeks

→ akathisia

Weeks to months

→ drug-induced parkinsonism

Months to years

→ tardive dyskinesia/tardive dystonia

The timing is approximate and overlap can occur.

Diagnostic Approach

When an abnormal movement occurs, determine:

• Exact type of movement
• Time of onset
• Recent medication changes
• Prescription and nonprescription drug exposure
• Withdrawal history
• Occupational or heavy-metal exposure
• Associated mental-status changes
• Autonomic findings
• Temperature
• Reflexes and clonus

The time relationship between drug exposure and movement onset is particularly useful.

Laboratory Evaluation

Testing should be guided by the suspected cause.

Possible investigations include:

• Glucose
• Electrolytes
• Calcium and magnesium
• Renal function
• Liver function
• Creatine kinase
• ECG

Targeted testing may include:

• Lithium concentration
• Anticonvulsant concentrations
• Heavy-metal testing when exposure is plausible
• Other drug-specific studies

Broad urine toxicology screening is usually less useful than targeted evaluation.

Neuroimaging

Movement disorders should not automatically be attributed to poisoning.

Brain imaging may be necessary when findings suggest:

• Stroke
• Intracranial hemorrhage
• Structural CNS disease
• Trauma
• Focal neurologic abnormalities

Management Principles

Treatment depends on the underlying syndrome.

General measures include:

• Stop or modify the causative medication when appropriate.
• Correct glucose and electrolyte abnormalities.
• Treat hyperthermia.
• Control seizures.
• Provide supportive care.

Important syndrome-specific treatments include:

Acute dystonia

→ diphenhydramine or benztropine

Akathisia

→ remove/reduce the causative agent when appropriate; selected symptomatic therapies may be used

Serotonin syndrome

→ discontinue serotonergic drugs, benzodiazepines, cooling, and selected use of cyproheptadine

NMS

→ discontinue dopamine antagonist, supportive care/cooling, with syndrome-specific therapy in severe cases

Cholinergic fasciculations

→ atropine for muscarinic manifestations plus pralidoxime in significant organophosphate poisoning

Tardive Dyskinesia Treatment

Management includes reassessing the responsible dopamine-blocking medication.

VMAT2 inhibitors such as valbenazine or deutetrabenazine are established treatments for clinically significant tardive dyskinesia.

Routine anticholinergic treatment may worsen tardive dyskinesia, even though anticholinergics are useful for acute dystonia and drug-induced parkinsonism.

Key Points

• Abnormal movements can provide important toxicologic diagnostic clues.
• Akathisia = inner restlessness with inability to remain still.
• Asterixis = brief loss of postural tone; myoclonus = sudden shock-like movement.
• Ethanol, sedatives, anticonvulsants, and lithium commonly produce ataxia.
• Dopamine-blocking antipsychotics and antiemetics commonly cause acute dystonia, akathisia, and parkinsonism.
• Acute dystonia commonly involves the eyes, jaw, tongue, and neck and usually responds to anticholinergic treatment.
• Fasciculations + excessive secretions + miosis strongly suggest cholinergic toxicity.
• PCP classically produces prominent nystagmus, including vertical nystagmus.
• Rigidity + hyperthermia should prompt consideration of NMS, serotonin syndrome, or malignant hyperthermia.
• Clonus and hyperreflexia strongly favor serotonin syndrome over NMS.
• Lithium toxicity can produce coarse tremor, ataxia, dysarthria, myoclonus, and other neurologic abnormalities.
• Tardive dyskinesia is a delayed complication of chronic dopamine-receptor blockade and may persist after drug discontinuation.
• Always consider metabolic and structural neurologic disease before assuming that an abnormal movement is toxicologic.

Toxicology – Methemoglobinemia

Definition

Methemoglobinemia occurs when hemoglobin iron is oxidized from its normal ferrous (Fe²⁺) state to the ferric (Fe³⁺) state.

Ferric hemoglobin, called methemoglobin (MetHb), cannot effectively bind oxygen.

Normally, MetHb represents approximately <1–2% of total hemoglobin.

Pathophysiology

Methemoglobinemia impairs oxygen delivery by two mechanisms:

1. Methemoglobin itself cannot carry oxygen effectively.
2. Methemoglobin increases the oxygen affinity of the remaining normal hemoglobin, shifting the oxyhemoglobin dissociation curve to the left.

Therefore:

Oxidation of Fe²⁺ → Fe³⁺ → reduced O₂-carrying capacity + impaired O₂ unloading → tissue hypoxia

This produces a form of functional anemia despite a potentially normal measured hemoglobin concentration and PaO₂.

Normal Reduction of Methemoglobin

Small amounts of methemoglobin are continuously generated and normally converted back to functional hemoglobin.

The major pathway uses:

Cytochrome b₅ reductase (NADH-dependent methemoglobin reductase)

A secondary NADPH-dependent pathway normally contributes little but becomes clinically important when methylene blue is administered.

Methylene Blue Mechanism

Methylene blue acts as an electron carrier.

In the presence of NADPH, it is converted to leucomethylene blue, which accelerates reduction of:

Fe³⁺ → Fe²⁺

NADPH production depends heavily on the pentose phosphate pathway and G6PD, explaining why methylene blue may be ineffective or harmful in significant G6PD deficiency.

Causes

Most acquired cases result from exposure to an oxidizing medication or chemical.

Important causes include:

• Benzocaine
• Prilocaine
• Dapsone
• Nitrates
• Nitrites
• Amyl/alkyl nitrites
• Aniline compounds
• Phenazopyridine
• Primaquine
• Sulfonamides
• Nitroglycerin and related nitrates
• Some industrial oxidizing chemicals

Benzocaine and dapsone are particularly important toxicologic causes.

Dapsone

Dapsone is notable because its metabolites are potent oxidants.

Toxicity may produce:

• Significant methemoglobinemia
• Hemolysis
• Recurrent or prolonged methemoglobinemia

Because of its pharmacokinetics and enterohepatic/enteric recycling, clinically important methemoglobinemia can recur after initial improvement.

Nitrites and Nitrates

Nitrites directly oxidize hemoglobin.

Nitrates can be converted to nitrites and may therefore produce methemoglobinemia.

Potential exposures include:

• Contaminated water
• Certain foods or chemicals
• Medications
• Recreational inhaled nitrites

Infants are particularly susceptible.

Infants

Young infants have increased susceptibility because:

• Fetal hemoglobin is more readily oxidized.
• Methemoglobin-reducing enzyme activity is relatively immature.
• Certain gastrointestinal conditions may increase nitrite production.

Thus, relatively modest oxidant exposure may cause more clinically important methemoglobinemia in infants.

Congenital Methemoglobinemia

Congenital causes include:

• Cytochrome b₅ reductase deficiency
• Hemoglobin M variants

Patients with congenital disease may have chronic cyanosis despite otherwise relatively few symptoms, depending on the specific disorder.

G6PD Deficiency

G6PD deficiency does not represent the usual mechanism of methemoglobinemia itself, but it is extremely important when choosing treatment.

Reduced G6PD activity limits production of NADPH.

Consequently, methylene blue may:

• Work poorly
• Increase oxidative stress
• Cause or worsen hemolysis

Significant G6PD deficiency therefore complicates treatment.

Clinical Features

Symptoms depend on:

• Methemoglobin concentration
• Rate of development
• Baseline hemoglobin
• Cardiopulmonary reserve
• Other causes of impaired oxygen delivery

Common manifestations include:

• Cyanosis
• Headache
• Fatigue
• Dizziness
• Dyspnea
• Tachycardia
• Tachypnea

More severe toxicity may cause:

• Confusion
• Syncope
• Chest pain
• Hypotension
• Dysrhythmias
• Seizures
• Coma
• Cardiovascular collapse

Cyanosis

Cyanosis is one of the classic findings.

It is often described as slate-gray, blue-gray, or brownish and may persist despite supplemental oxygen.

A patient with:

Persistent cyanosis + relatively preserved PaO₂ + unusual pulse-oximetry findings

should raise strong suspicion for dyshemoglobinemia.

Chocolate-Brown Blood

Blood containing substantial methemoglobin may appear dark or chocolate brown rather than normally bright red.

This appearance is a useful clue but does not replace laboratory confirmation.

Severity and MetHb Level

Symptoms generally become more likely as the MetHb percentage rises, but rigid concentration thresholds are unreliable.

Broadly:

• Low levels: often asymptomatic
• Moderate levels: cyanosis, headache, dizziness, fatigue, dyspnea
• Higher levels: confusion, syncope, chest pain, marked hypoxia symptoms
• Severe levels: seizures, dysrhythmias, shock, coma
• Very high levels: potentially fatal

Treatment should therefore be based on the patient’s symptoms, MetHb concentration, underlying disease, and ongoing oxidant exposure, rather than concentration alone.

Higher-Risk Patients

Symptoms can develop at lower MetHb concentrations in patients with:

• Anemia
• Coronary artery disease
• Heart failure
• Significant pulmonary disease
• Sepsis or shock
• Other conditions reducing oxygen delivery

Pregnancy and infancy also warrant particular caution.

Pulse Oximetry

Standard two-wavelength pulse oximetry is unreliable in methemoglobinemia.

As MetHb rises, the displayed oxygen saturation tends to drift toward approximately the mid-80% range, often around 85%, regardless of the actual arterial oxygen content.

Thus, an SpO₂ that remains near the mid-80s despite oxygen therapy is a classic clue.

PaO₂ Can Be Normal

A major diagnostic pitfall is assuming that a normal arterial PaO₂ excludes serious hypoxia.

PaO₂ measures oxygen dissolved in plasma.

It does not directly measure how much oxygen hemoglobin is actually carrying.

Therefore:

Methemoglobinemia → normal/high PaO₂ may coexist with severely impaired hemoglobin-mediated oxygen delivery

Saturation Gap

A saturation gap may occur when:

• Calculated arterial oxygen saturation from a blood gas appears normal or high,
• while pulse oximetry shows substantially lower saturation.

This discrepancy should raise suspicion for a dyshemoglobinemia such as:

• Methemoglobinemia
• Carboxyhemoglobinemia

However, direct co-oximetry is preferred for diagnosis.

Co-Oximetry

Co-oximetry is the diagnostic test of choice.

Unlike ordinary pulse oximetry, it uses multiple wavelengths to distinguish:

• Oxyhemoglobin
• Deoxyhemoglobin
• Methemoglobin
• Carboxyhemoglobin

The MetHb percentage should therefore be directly measured, not inferred from standard oxygen saturation.

Evaluation

Important investigations include:

• Co-oximetry with MetHb measurement
• ECG
• CBC
• Electrolytes
• Renal function
• Blood gas when clinically indicated

Depending on severity or suspected toxicant:

• Lactate
• Hemolysis studies
• Liver tests
• Targeted toxicology testing

G6PD testing may be useful but generally should not delay emergency management.

Hemolysis

Some oxidant exposures can cause both:

• Methemoglobinemia
• Oxidative hemolytic anemia

This is particularly relevant with agents such as:

• Dapsone
• Naphthalene
• Primaquine
• Other strong oxidants

Evidence of hemolysis may include:

• Falling hemoglobin
• Elevated bilirubin
• Elevated LDH
• Reduced haptoglobin
• Abnormal peripheral smear

Initial Management

The first steps are:

• Stop exposure to the causative agent.
• Support airway and ventilation as necessary.
• Administer supplemental oxygen.
• Obtain co-oximetry.
• Assess for cardiovascular or neurologic evidence of tissue hypoxia.

Supplemental oxygen does not directly convert methemoglobin back to normal hemoglobin, but it maximizes oxygenation of the remaining functional hemoglobin.

Methylene Blue

Methylene blue is the standard antidote for clinically significant acquired methemoglobinemia.

It is particularly considered when there is:

• Significant symptomatic methemoglobinemia
• Neurologic dysfunction
• Cardiovascular manifestations
• Significant or rising MetHb concentration

Patients with impaired oxygen-delivery reserve may warrant treatment at a lower MetHb level than otherwise healthy patients.

Important Methylene Blue Precautions

Methylene blue requires caution in G6PD deficiency because adequate NADPH production is required for its therapeutic action.

It can also cause oxidative hemolysis.

Excessive methylene blue exposure can paradoxically act as an oxidant and worsen methemoglobinemia.

Therefore, repeated treatment should not continue automatically when the patient fails to respond as expected.

Methylene Blue and Serotonin Toxicity

An important modern safety consideration is that methylene blue has monoamine oxidase-A inhibitory activity.

In patients receiving serotonergic medications, it can precipitate serotonin toxicity, particularly with substantial systemic exposure.

When methylene blue is urgently required for life-threatening methemoglobinemia, the immediate oxygen-delivery problem must still be addressed, but serotonergic medications and interaction risk should be reviewed.

When Methylene Blue Fails

Failure to improve should prompt consideration of:

• G6PD deficiency
• Continued oxidant absorption
• Recurrent toxicity from the responsible drug
• Incorrect diagnosis
• Sulfhemoglobinemia
• Inadequate response requiring specialist treatment

Toxicology consultation is particularly useful in refractory cases.

Alternative and Rescue Therapies

For severe methemoglobinemia when methylene blue is contraindicated or ineffective, specialist-directed options can include:

• Ascorbic acid
• Exchange transfusion
• Red-cell transfusion in selected circumstances
• Hyperbaric oxygen as an uncommon rescue strategy

Ascorbic acid reduces methemoglobin relatively slowly and is generally not a substitute for methylene blue in an immediately life-threatening case when methylene blue can safely be used.

Sulfhemoglobinemia

Sulfhemoglobinemia can closely resemble methemoglobinemia.

Features include:

• Persistent cyanosis
• Abnormal dyshemoglobin measurement
• Poor or absent response to methylene blue

Unlike methemoglobin, sulfhemoglobin cannot simply be enzymatically reduced back to normal hemoglobin.

Resolution therefore depends largely on replacement of affected erythrocytes over time.

Decontamination

For dermal exposure:

• Remove contaminated clothing.
• Wash exposed skin thoroughly.

For ingestion, gastrointestinal decontamination is not automatic.

Induced vomiting and routine gastric lavage are outdated approaches.

Activated charcoal may be considered for selected recent ingestions when:

• The causative substance is adsorbed,
• Clinically meaningful exposure occurred, and
• The airway is adequately protected.

Monitoring

Significant cases require:

• Continuous cardiac monitoring
• Respiratory monitoring
• Serial neurologic examinations
• Repeat MetHb measurements
• Assessment for recurrent toxicity

Recurrent measurements are particularly important after exposures such as dapsone, where methemoglobinemia can return after initial improvement.

Prognosis

Most acquired cases have an excellent outcome when:

• The oxidant exposure is stopped
• Tissue hypoxia is recognized promptly
• Appropriate treatment is provided

Severe untreated methemoglobinemia can cause:

• Myocardial ischemia
• Dysrhythmias
• Seizures
• Shock
• Coma
• Death

Key Points

• Methemoglobinemia results from oxidation of hemoglobin iron from Fe²⁺ to Fe³⁺.
• Methemoglobin cannot effectively carry oxygen and also causes a left shift of the remaining oxyhemoglobin dissociation curve.
• Classic causes include benzocaine, dapsone, nitrates/nitrites, aniline compounds, phenazopyridine, primaquine, and inhaled alkyl nitrites.
• Think of methemoglobinemia when there is cyanosis that does not improve as expected with oxygen.
• Blood may appear characteristically chocolate brown.
• Standard pulse oximetry is unreliable and often trends toward approximately 85%.
• PaO₂ can remain normal because it measures dissolved oxygen rather than hemoglobin oxygen-carrying capacity.
• Diagnosis is confirmed with co-oximetry.
• Methylene blue is the standard antidote for clinically significant acquired methemoglobinemia.
• Use methylene blue cautiously in G6PD deficiency, where it may be ineffective and can worsen hemolysis.
• Methylene blue also has MAO-A inhibitory activity and can interact with serotonergic medications.
• Dapsone can cause prolonged or recurrent methemoglobinemia, so continued monitoring may be necessary.
• Failure to respond to methylene blue should raise concern for continued oxidant exposure, G6PD deficiency, or sulfhemoglobinemia.

Toxicology – Metal Fume Fever

Definition

Metal fume fever is an acute, self-limited inhalational illness caused by breathing freshly generated metal oxide fumes, classically during welding, cutting, brazing, smelting, or heating galvanized metal.

The classic cause is zinc oxide, particularly from welding galvanized steel.

Other implicated metal fumes include oxides of:

• Copper
• Magnesium
• Aluminum
• Manganese
• Iron
• Nickel
• Chromium

Historical names include welder’s fever, zinc shakes, brass chills, and Monday fever.

Pathophysiology

Heating metals can generate very small respirable metal oxide particles that penetrate deeply into the lungs.

The current understanding emphasizes an acute inflammatory response in the respiratory tract, with activation of alveolar macrophages and release of inflammatory cytokines.

This produces a transient systemic influenza-like syndrome.

Metal fume fever is therefore primarily an inflammatory response rather than a classic allergic reaction or systemic heavy-metal poisoning.

Important Distinction: Cadmium

Cadmium fume inhalation is not simply ordinary metal fume fever.

Cadmium can cause severe delayed:

• Chemical pneumonitis
• Noncardiogenic pulmonary edema
• ARDS
• Respiratory failure
• Systemic toxicity

Therefore, the specific metal involved must be identified whenever possible.

Occupational Exposures

Common settings include:

• Welding
• Cutting galvanized steel
• Brazing
• Soldering
• Metal smelting
• Foundry work
• Metal reclamation/recycling
• Grinding or fabrication
• Furnace operations

Exposure frequently occurs when adequate local exhaust ventilation or respiratory protection is absent.

Onset

Symptoms typically begin several hours after exposure, commonly about 4–12 hours later.

Because of this delay, a worker may feel well during the exposure and become ill later that evening.

Clinical Features

The illness resembles an acute viral syndrome.

Common symptoms include:

• Fever
• Chills
• Malaise
• Fatigue
• Headache
• Myalgia
• Arthralgia
• Weakness
• Sweating

Respiratory symptoms may include:

• Dry cough
• Chest tightness
• Dyspnea
• Sore throat
• Wheezing
• Pleuritic chest discomfort

A metallic or unusual taste may occur shortly after exposure.

Monday Fever

Repeated exposure can produce temporary tolerance or tachyphylaxis.

Workers may experience:

• Strong symptoms after returning to work following several exposure-free days
• Diminishing symptoms with repeated exposure during the week
• Recurrence after another exposure-free interval

This phenomenon produced the historical term “Monday morning fever.”

Importantly, temporary tolerance does not mean that continued inhalation of welding fumes is safe.

Physical Examination

Findings may include:

• Fever
• Tachycardia
• Tachypnea
• Diaphoresis

Pulmonary examination may be:

• Normal
• Mildly abnormal with wheezing or crackles

Marked hypoxemia, severe respiratory distress, or substantial abnormal lung findings should prompt investigation for a more serious inhalational injury rather than uncomplicated metal fume fever.

Diagnosis

Diagnosis is primarily clinical.

The most important diagnostic clue is:

Recent metal-fume exposure + delayed influenza-like illness + spontaneous improvement after removal from exposure

A careful occupational history is therefore essential.

Ask about:

• Welding or cutting
• Galvanized metal
• Type of metal/alloy
• Coatings on the metal
• Ventilation
• Confined-space exposure
• Other workers with similar symptoms
• Potential exposure to cadmium or other highly toxic metals

Laboratory Findings

No laboratory test specifically confirms metal fume fever.

Possible nonspecific findings include:

• Leukocytosis
• Mild inflammatory abnormalities

Serum or urine metal concentrations are generally not useful for diagnosing uncomplicated metal fume fever.

Targeted metal testing may be appropriate when a specific toxic metal exposure is suspected.

Chest Radiograph

Chest radiography is usually normal in uncomplicated metal fume fever.

A radiograph may be appropriate when there is:

• Significant dyspnea
• Hypoxemia
• Persistent respiratory symptoms
• Abnormal lung examination
• Concern for pneumonitis or pulmonary edema

Substantial infiltrates should raise concern for an alternative or more severe inhalational injury.

Differential Diagnosis

Important alternatives include:

• Viral respiratory infection
• Bacterial pneumonia
• COVID-19 or influenza
• Chemical pneumonitis
• Occupational asthma
• Hypersensitivity pneumonitis
• Polymer fume fever
• Chlorine or other irritant-gas exposure
• Nitrogen dioxide exposure
• Pulmonary embolism
• Sepsis

Particularly important occupational toxic exposures include:

• Cadmium fumes
• Nickel carbonyl
• Other severe metal or combustion-product exposures

Metal Fume Fever vs. Cadmium Pneumonitis

Metal fume fever

• Influenza-like illness
• Usually begins several hours after exposure
• Chest radiograph usually normal
• Usually resolves within 1–2 days
• Serious pulmonary injury is unusual

Cadmium fume toxicity

• Can initially resemble metal fume fever
• May progress to severe respiratory symptoms
• Chemical pneumonitis/pulmonary edema may develop
• Can cause systemic toxicity
• Potentially life-threatening

Failure to distinguish these conditions is an important diagnostic pitfall.

Management

There is no specific antidote for uncomplicated metal fume fever.

Treatment is primarily:

• Termination of exposure
• Rest
• Adequate hydration
• Symptomatic treatment of fever and pain
• Oxygen when hypoxemia is present

Most patients improve rapidly once exposure stops.

Bronchospasm

If clinically significant bronchospasm occurs, an inhaled beta₂-agonist bronchodilator may be used.

The source recommends routine systemic corticosteroids for bronchospasm, but corticosteroids are not routinely required for uncomplicated metal fume fever.

They may be considered when a separate condition such as significant reactive airway disease or another inflammatory pulmonary process is present.

Antibiotics

Prophylactic antibiotics have no established role in uncomplicated metal fume fever because this is not a bacterial infection.

Antibiotics should be used only when there is evidence of a bacterial infectious process.

Decontamination

The most important intervention is removal from further inhalational exposure.

If clothing or skin is significantly contaminated with metal-containing dust:

• Remove contaminated clothing.
• Wash exposed skin.

Extensive decontamination is generally unnecessary after isolated inhalation of metal fumes when there is no ongoing surface contamination.

Prognosis

Uncomplicated metal fume fever has an excellent prognosis.

Typical course:

Exposure → latent period of several hours → influenza-like symptoms → improvement within approximately 24–48 hours

Persistent or worsening symptoms should prompt reconsideration of the diagnosis.

Warning Signs

Features inconsistent with simple metal fume fever include:

• Progressive dyspnea
• Significant hypoxemia
• Hemoptysis
• Persistent high fever
• Pulmonary infiltrates
• Pulmonary edema
• Severe chest pain
• Neurologic abnormalities
• Renal or hepatic injury
• Symptoms lasting substantially beyond the expected course

These findings should raise concern for cadmium toxicity, chemical pneumonitis, infection, or another serious exposure.

Prevention

Prevention is central because recurrence follows re-exposure.

Occupational measures include:

• Adequate local exhaust ventilation
• Appropriate respiratory protection
• Identification of metal composition and surface coatings
• Avoidance of welding in poorly ventilated or confined spaces without proper controls
• Occupational-health assessment after recurrent episodes

Repeated episodes should not simply be accepted as an unavoidable consequence of welding.

Key Points

• Metal fume fever is an acute, self-limited inflammatory illness following inhalation of metal oxide fumes.
• Zinc oxide from welding galvanized steel is the classic cause.
• Symptoms typically appear several hours after exposure and resemble influenza.
• Common manifestations are fever, chills, myalgia, headache, fatigue, cough, and chest tightness.
• Repeated exposure can produce temporary tolerance, explaining the term “Monday fever.”
• Diagnosis is primarily based on a careful occupational exposure history.
• Chest radiography is usually normal in uncomplicated disease.
• Serum or urine metal measurements are usually unnecessary for straightforward metal fume fever.
• Treatment is primarily removal from exposure and supportive care.
• Antibiotics and systemic corticosteroids are not routinely indicated for uncomplicated disease.
• Symptoms usually resolve within 24–48 hours.
• Cadmium fume pneumonitis must not be mistaken for benign metal fume fever, because cadmium inhalation can cause severe delayed lung injury and respiratory failure.

Toxicology – Hypothermia

Definition

Hypothermia is a core body temperature below 35°C (95°F).

A commonly used clinical classification is:

• Mild: 32–35°C
• Moderate: 28–32°C
• Severe: <28°C

Clinical findings do not always correspond perfectly to a specific temperature, so management should consider both core temperature and physiologic condition.

Pathophysiology

The hypothalamus normally maintains temperature through:

• Peripheral vasoconstriction
• Shivering
• Increased metabolic heat production
• Behavioral responses to cold

With progressive cooling:

Cold exposure → vasoconstriction + shivering → depletion of energy reserves → impaired thermoregulation → CNS/cardiovascular depression

At lower temperatures:

• Shivering eventually stops.
• Metabolic rate falls.
• Cardiac conduction slows.
• Myocardial irritability increases.
• Consciousness progressively decreases.

Toxicologic hypothermia commonly occurs when intoxication impairs consciousness or judgment, preventing the patient from recognizing or escaping a cold environment.

Major Toxicologic Causes

Important causes include:

• Ethanol
• Opioids
• Sedative-hypnotics
• Clonidine and imidazolines
• Antipsychotic medications
• Other CNS depressants

Many drugs cause hypothermia indirectly by producing:

• Immobility
• CNS depression
• Vasodilation
• Impaired behavioral responses
• Reduced shivering or metabolic heat production

Ethanol

Alcohol intoxication predisposes to hypothermia through:

• Impaired judgment
• CNS depression
• Reduced behavioral response to cold
• Peripheral vasodilation
• Prolonged environmental exposure

A blood ethanol concentration can document exposure but should not automatically be assumed to explain profound hypothermia or altered consciousness.

Opioids

Opioid poisoning may cause:

• CNS depression
• Respiratory depression
• Miosis
• Immobility

These effects increase the risk of environmental hypothermia.

When opioid-induced respiratory depression is suspected, naloxone should be used to restore adequate ventilation.

Sedative-Hypnotics

Benzodiazepines, barbiturates, and other sedatives can predispose to hypothermia through:

• CNS depression
• Immobility
• Reduced protective behavior
• Prolonged exposure to cold

Severe intoxication can additionally produce respiratory depression and hypotension.

Routine urine drug screens may miss clinically important sedatives and therefore cannot reliably exclude poisoning.

Carbon Monoxide

Carbon monoxide exposure should be considered when hypothermia occurs with:

• Headache
• Confusion
• Syncope
• Coma
• Metabolic/lactic acidosis
• Exposure to combustion products

Carboxyhemoglobin measurement by co-oximetry is used to confirm exposure.

Standard pulse oximetry may appear deceptively normal.

Hypoglycemic Agents

Hypoglycemia can contribute to:

• Altered mental status
• Reduced heat production
• Hypothermia

Therefore, bedside glucose should be checked early in every significantly hypothermic patient.

Nontoxicologic Causes

Important alternatives include:

• Environmental exposure
• Sepsis
• Hypoglycemia
• Hypothyroidism/myxedema coma
• Adrenal insufficiency
• CNS injury
• Trauma
• Stroke
• Malnutrition

Any disorder causing altered consciousness can indirectly produce hypothermia by preventing escape from a cold environment.

Mild Hypothermia

Typical findings include:

• Shivering
• Tachycardia
• Tachypnea
• Peripheral vasoconstriction
• Ataxia
• Dysarthria
• Impaired judgment

Patients are often still capable of generating substantial endogenous heat.

Moderate Hypothermia

As temperature falls:

• Shivering decreases or disappears
• Consciousness deteriorates
• Bradycardia develops
• Respiratory rate falls
• Cardiac conduction slows
• Dysrhythmias become increasingly possible

An Osborn (J) wave may appear on ECG.

Severe Hypothermia

Severe hypothermia can produce:

• Coma
• Marked bradycardia
• Hypotension
• Hypoventilation
• Loss of reflexes
• Ventricular dysrhythmias
• Ventricular fibrillation
• Asystole

Vital signs may become extremely difficult to detect.

Cardiovascular Effects

The usual progression is:

Early tachycardia → progressive bradycardia → conduction slowing → increasing dysrhythmia risk

ECG abnormalities can include:

• Sinus bradycardia
• PR prolongation
• QRS widening
• QT prolongation
• Atrial dysrhythmias
• Osborn waves
• Ventricular fibrillation

Osborn (J) Waves

The Osborn wave is a positive deflection near the J point, immediately following the QRS complex.

It is strongly associated with hypothermia but is not specific.

J waves can also occur in other clinical settings and their absence does not exclude significant hypothermia.

Neurologic Effects

Progressive cooling causes:

• Impaired judgment
• Ataxia
• Dysarthria
• Confusion
• Lethargy
• Loss of reflexes
• Coma

Profound CNS depression in severe hypothermia can mimic death.

Respiratory Effects

Early cooling may cause tachypnea.

With worsening hypothermia:

• Respiratory rate falls
• Tidal volume decreases
• Protective airway reflexes disappear
• Hypoventilation develops
• Aspiration risk increases

Cold Diuresis

Peripheral vasoconstriction shifts blood centrally, which promotes renal excretion of water and electrolytes.

This cold diuresis can produce significant intravascular volume depletion.

During rewarming, peripheral vasodilation may then reveal or worsen hypotension.

Acid-Base Abnormalities

Hypothermia can produce complex acid-base disturbances.

Possible abnormalities include:

• Early respiratory alkalosis
• Later respiratory acidosis from hypoventilation
• Lactic acidosis from impaired perfusion
• Mixed acid-base disorders

Blood-gas interpretation in severe hypothermia requires awareness that laboratory analyzers generally measure samples at standard temperature.

Potassium

Potassium concentrations can change substantially during cooling and rewarming.

Hypokalemia may occur from intracellular redistribution, but potassium management must be cautious because potassium can move back extracellularly during rewarming.

Marked hyperkalemia in profound hypothermia can also indicate severe cellular injury and may carry important prognostic information.

Glucose

Both hyperglycemia and hypoglycemia can occur.

Hypoglycemia is particularly important because it:

• Causes altered consciousness
• Impairs shivering
• Reduces heat production
• Is rapidly treatable

Laboratory Evaluation

Significant hypothermia may warrant:

• Bedside glucose
• Electrolytes
• Renal function
• CBC
• Creatine kinase
• Blood gas
• Lactate
• Coagulation studies
• ECG

Depending on circumstances:

• Ethanol concentration
• Carboxyhemoglobin
• Acetaminophen and salicylate concentrations
• Thyroid/adrenal testing
• Other targeted toxicology studies

Core Temperature

Accurate core-temperature measurement is essential.

In significant accidental hypothermia, a low-reading core thermometer should be used.

Depending on the clinical setting, appropriate measurement sites include:

• Rectal
• Esophageal
• Bladder

Peripheral skin, oral, or axillary measurements may substantially underestimate or inaccurately reflect core temperature.

Initial Management

Priorities are:

Prevent further cooling → stabilize ABCs → begin appropriate rewarming → treat the underlying cause

Initial measures include:

• Remove wet clothing.
• Insulate the patient.
• Move to a warm environment.
• Handle gently.
• Assess airway and ventilation.
• Check glucose.
• Establish vascular access when required.
• Begin continuous cardiac monitoring in significant hypothermia.

Gentle Handling

Patients with severe hypothermia should be handled carefully.

The severely cold myocardium is electrically unstable, and unnecessary vigorous movement has historically been associated with precipitation of dangerous dysrhythmias.

Necessary resuscitative procedures should still be performed.

Passive External Rewarming

Passive rewarming involves:

• Removing wet clothing
• Drying the patient
• Insulation with blankets
• Providing a warm environment

It is generally appropriate for mild hypothermia when the patient retains adequate endogenous heat production.

Active External Rewarming

Methods include:

• Forced-air warming blankets
• Other controlled external heating systems

Active external warming is particularly useful when passive measures alone are inadequate.

Heat is generally focused on the trunk/core rather than aggressively warming the extremities first.

Active Internal Rewarming

More severe hypothermia may require:

• Warmed IV fluids
• Warmed humidified respiratory gases as an adjunct
• Extracorporeal rewarming in severe cases

Older methods such as routine gastric, bladder, or peritoneal lavage have largely been displaced by more effective and safer contemporary approaches and are not routine rewarming methods.

Warmed IV Fluids

Warmed isotonic crystalloid is useful when fluid resuscitation is required.

Its primary roles are:

• Preventing additional cooling
• Treating hypovolemia

Warmed fluids alone generally provide relatively limited heat transfer and should not be considered sufficient treatment for profound hypothermia.

Extracorporeal Rewarming

Extracorporeal life support (ECLS), particularly VA-ECMO, provides the most effective rewarming for selected patients with severe hypothermia and cardiovascular instability or cardiac arrest.

It provides:

• Rapid core rewarming
• Oxygenation
• Circulatory support

Cardiopulmonary bypass is another extracorporeal option where ECMO is unavailable.

The source’s emphasis on femoral-femoral bypass and open pleural lavage reflects older practice; modern management generally favors ECMO/ECLS when available for hypothermic cardiac arrest.

Hypothermic Cardiac Arrest

Severe hypothermia can produce extraordinarily low metabolic requirements, meaning apparently lifeless patients may occasionally survive prolonged arrest when appropriately rewarmed.

Therefore, traditional prognostic rules used in normothermic cardiac arrest cannot simply be applied.

The older statement that resuscitation is futile if circulation does not return within about 30 minutes after rewarming is not considered a reliable modern stopping rule.

Decisions regarding termination of resuscitation should incorporate:

• Mechanism
• Core temperature
• Potassium and other prognostic markers
• Evidence of lethal injury
• Duration and circumstances of arrest
• Availability of extracorporeal rewarming

Defibrillation and Medications

The severely hypothermic myocardium may respond poorly to:

• Defibrillation
• Vasopressors
• Antiarrhythmic medications

Modern resuscitation follows hypothermia-specific cardiac-arrest protocols, with modifications according to core temperature.

Repeated accumulation of medications during profound hypothermia should be avoided because drug metabolism is markedly reduced and concentrations may rise during rewarming.

Bradycardia

Bradycardia is an expected physiologic response to significant hypothermia.

The primary treatment is generally:

Rewarming

Attempts to normalize the heart rate pharmacologically are often unnecessary unless another process is clearly contributing.

Decontamination

Do not induce vomiting.

Routine gastric lavage in a hypothermic poisoned patient is not standard modern management.

Activated charcoal may occasionally be appropriate after a selected ingestion, but airway safety is essential and rewarming/resuscitation takes priority.

Complications During Rewarming

Potential complications include:

• Hypotension
• Dysrhythmias
• Electrolyte shifts
• Rhabdomyolysis
• Acute kidney injury
• Coagulopathy
• Pulmonary edema
• Rewarming-related vasodilation

Patients with moderate or severe hypothermia therefore require continued monitoring even after the temperature begins to normalize.

Monitoring

Monitor:

• Core temperature
• ECG and cardiac rhythm
• Blood pressure/perfusion
• Respiratory function
• Glucose
• Electrolytes
• Renal function
• Acid-base status

Severe cases may require invasive hemodynamic monitoring and intensive care.

Key Points

• Hypothermia = core temperature <35°C.
• Toxicologic hypothermia commonly occurs because intoxication causes CNS depression, immobility, impaired judgment, or reduced ability to escape cold exposure.
• Important causes include ethanol, opioids, sedative-hypnotics, clonidine/imidazolines, and other CNS depressants.
• Progressive cooling produces CNS depression, bradycardia, conduction slowing, and increasing risk of ventricular dysrhythmias.
• Osborn (J) waves are classically associated with hypothermia but are not specific.
• Check glucose early because hypoglycemia can both cause and worsen hypothermia.
• Cold diuresis can cause substantial volume depletion.
• Mild cases may respond to passive/active external warming; severe unstable hypothermia may require extracorporeal rewarming.
• VA-ECMO/ECLS is preferred when available for selected patients with hypothermic cardiac arrest or profound cardiovascular instability.
• Bradycardia from hypothermia is primarily treated by rewarming, rather than attempts to force the heart rate back to normal.
• Profound hypothermia can mimic death; conventional normothermic cardiac-arrest prognostic rules should not be applied uncritically.
• Significant complications can emerge during rewarming, so moderate-to-severe cases require continued close monitoring.

Toxicology – Hypotension and Shock

Definition

Hypotension is blood pressure that is abnormally low for the patient’s age and physiologic state.

In adults, systolic BP <90 mm Hg or mean arterial pressure (MAP) <65 mm Hg is commonly used as a practical warning threshold, but a single numerical cutoff does not define adequate circulation.

Shock means inadequate tissue perfusion and oxygen delivery, which may occur with or without marked hypotension.

Signs of impaired perfusion include:

• Altered mental status
• Cool or mottled extremities
• Delayed capillary refill
• Weak peripheral pulses
• Oliguria
• Elevated lactate
• Metabolic acidosis

Pathophysiology

Toxicologic hypotension can result from several mechanisms:

1. Myocardial depression

• Beta-blockers
• Calcium-channel blockers
• Some sodium-channel blockers

2. Vasodilation

• Alpha-adrenergic blockade
• Sedative agents
• Vasodilators
• Severe distributive toxicity

3. Bradycardia or conduction failure

• Beta-blockers
• Calcium-channel blockers
• Digoxin
• Cholinergic agents
• Clonidine/imidazolines

4. Dysrhythmias

• Sodium-channel blockers
• Digoxin
• Sympathomimetics
• Theophylline

5. Hypovolemia

• Vomiting/diarrhea
• Hemorrhage
• Excessive sweating
• Third-spacing or capillary leak

6. Hypoxia or metabolic derangement

• Severe hypoxemia
• Acidosis
• Electrolyte abnormalities
• Hypothermia

Several mechanisms may occur simultaneously.

Major Toxicologic Causes

Important causes include:

• Beta-blockers
• Calcium-channel blockers
• Digoxin and other cardiac glycosides
• Tricyclic antidepressants and other sodium-channel blockers
• Clonidine and imidazolines
• Opioids
• Sedative-hypnotics
• Organophosphates/carbamates
• Iron
• Theophylline
• Severe sympathomimetic poisoning
• Vasodilators

Beta-Blocker Toxicity

Typical findings include:

• Hypotension
• Bradycardia
• AV block
• Reduced myocardial contractility
• CNS depression

Some beta-blockers can additionally cause:

• Seizures
• QRS widening
• Ventricular dysrhythmias

Hypoglycemia can occur, particularly in children or severe poisoning.

The source’s association of beta-blocker poisoning with hyperglycemia is less characteristic; hyperglycemia is a more useful clue to calcium-channel blocker toxicity.

Calcium-Channel Blocker Toxicity

Severe poisoning can produce:

• Hypotension
• Bradycardia
• AV block
• Myocardial depression
• Vasodilation
• Shock

Hyperglycemia is an important diagnostic clue because calcium-channel blockade impairs pancreatic insulin release.

Severe cases can progress to profound cardiogenic and vasodilatory shock.

Digoxin Toxicity

Possible findings include:

• Nausea/vomiting
• Bradycardia
• AV block
• Ventricular dysrhythmias
• Visual disturbances
• Hypotension

Acute severe poisoning may produce hyperkalemia.

Digoxin immune Fab is the definitive antidote for life-threatening cardiac glycoside toxicity.

Clonidine and Imidazolines

These can produce:

• CNS depression
• Miosis
• Bradycardia
• Hypotension
• Respiratory depression

A brief initial hypertensive phase may precede hypotension.

This presentation can closely resemble opioid poisoning.

Opioids

The classic toxidrome includes:

• CNS depression
• Respiratory depression
• Miosis

Hypotension can develop in severe poisoning, especially with:

• Hypoxia
• Vasodilation
• Coingestants

When opioid-induced respiratory depression is suspected, naloxone is indicated, with the goal of restoring adequate ventilation rather than necessarily complete consciousness.

Cholinergic Poisoning

Organophosphate and carbamate poisoning may produce:

• Miosis
• Salivation
• Lacrimation
• Sweating
• Bronchorrhea
• Bronchospasm
• Vomiting/diarrhea
• Bradycardia
• Hypotension

Nicotinic effects include:

• Fasciculations
• Weakness
• Paralysis

Severe hypotension may accompany respiratory failure and profound cholinergic toxicity.

Sodium-Channel Blockade

Tricyclic antidepressants are the classic example.

Findings include:

• Hypotension
• Tachycardia
• CNS depression
• Seizures
• QRS widening
• Ventricular dysrhythmias

An ECG showing QRS widening and a prominent terminal R wave in aVR supports significant sodium-channel blockade.

Sodium bicarbonate is a key treatment for clinically important TCA/sodium-channel-blocking cardiotoxicity.

Iron Poisoning

Severe iron toxicity can produce:

• Vomiting
• Abdominal pain
• GI bleeding
• High-anion-gap metabolic acidosis
• CNS depression
• Hypotension/shock
• Hepatic injury

Shock may result from GI fluid loss, vasodilation, mitochondrial toxicity, and cardiovascular dysfunction.

Sympathomimetics

Cocaine and amphetamine-type stimulants usually initially cause:

• Hypertension
• Tachycardia
• Agitation
• Hyperthermia

Severe poisoning can later progress to hypotension from:

• Dysrhythmias
• Myocardial ischemia/dysfunction
• Severe hyperthermia
• Acidosis
• Volume depletion
• Cardiovascular collapse

Clinical Clues

Hypotension + bradycardia + hyperglycemia

→ consider calcium-channel blocker toxicity

Hypotension + bradycardia + CNS depression ± hypoglycemia

→ consider beta-blocker toxicity

Hypotension + miosis + respiratory depression

→ opioid or clonidine/imidazoline toxicity

Hypotension + miosis + bronchorrhea + secretions

→ cholinergic syndrome

Hypotension + QRS widening + seizures

→ sodium-channel blocker toxicity

Hypotension + dysrhythmia + GI symptoms + hyperkalemia

→ consider digoxin toxicity

Nontoxicologic Causes

Do not assume hypotension is caused by poisoning.

Important alternatives include:

• Sepsis
• Hemorrhage
• Dehydration
• Myocardial infarction
• Pulmonary embolism
• Cardiac tamponade
• Tension pneumothorax
• Anaphylaxis
• Spinal/neurogenic shock
• Adrenal crisis
• Hypothermia

Evaluation

Immediate assessment should focus on:

• Airway
• Breathing
• Circulation
• Mental status
• Peripheral perfusion
• Urine output
• Temperature

Important investigations include:

• ECG
• Continuous cardiac monitoring
• Bedside glucose
• Electrolytes
• Renal function
• Acid-base assessment when indicated

Depending on presentation:

• Lactate
• Troponin
• Creatine kinase
• Digoxin concentration
• Acetaminophen/salicylate concentrations
• Bedside ultrasound/echocardiography
• Other targeted toxicology tests

Routine urine toxicology screens have limited ability to identify the cause of shock.

ECG

ECG findings can provide major diagnostic clues.

Look for:

• Bradycardia
• AV block
• QRS widening
• QT prolongation
• Ventricular dysrhythmias
• Myocardial ischemia

Continuous monitoring is appropriate in significant poisoning-associated hypotension.

Initial Management

Management follows standard resuscitation priorities:

• Ensure adequate airway and ventilation.
• Provide oxygen when indicated.
• Establish vascular access.
• Obtain continuous cardiac monitoring.
• Check glucose.
• Correct major electrolyte abnormalities.
• Treat seizures, hypoxia, and severe temperature abnormalities.
• Identify and treat the responsible toxicant.

Endotracheal intubation is based on failure of oxygenation/ventilation or inability to protect the airway, not hypotension alone.

IV Fluids

Isotonic crystalloid may be appropriate when:

• Hypovolemia is suspected
• There is no evidence of major fluid overload

However, repeated large fluid boluses may be harmful when the dominant problem is drug-induced myocardial depression.

Fluid therapy should therefore be individualized using:

• Clinical perfusion
• Lung examination
• Urine output
• Bedside ultrasound when available
• Hemodynamic response

Vasopressors

Persistent shock despite appropriate initial measures generally requires vasopressor therapy.

Norepinephrine is commonly used for vasodilatory shock and is often a preferred initial vasopressor in undifferentiated severe hypotension.

The optimal agent can differ according to the poison and mechanism.

The source’s routine sequence of dopamine followed by norepinephrine is outdated; dopamine is no longer the universal first-line vasopressor for poisoned hypotensive patients.

High-Dose Insulin Euglycemia Therapy

High-dose insulin therapy is an important treatment for severe:

• Calcium-channel blocker poisoning
• Beta-blocker poisoning

It improves myocardial energy utilization and contractility.

Close monitoring is required for:

• Hypoglycemia
• Hypokalemia
• Fluid and glucose requirements

Calcium

IV calcium is particularly useful in calcium-channel blocker toxicity.

It may temporarily improve:

• Contractility
• Blood pressure
• Cardiac conduction

Because the effect may be incomplete or temporary, severe poisoning often requires additional therapies.

Glucagon

Glucagon can improve heart rate and contractility in beta-blocker poisoning by increasing intracellular cAMP through a receptor independent of the beta-adrenergic receptor.

It may be used as an adjunct, although modern severe beta-blocker poisoning management frequently relies heavily on vasopressors and high-dose insulin therapy.

Sodium Bicarbonate

Sodium bicarbonate is indicated for clinically important cardiac sodium-channel blockade, particularly when there is:

• QRS widening
• Ventricular dysrhythmia
• Significant hypotension attributable to sodium-channel blockade

TCAs are the classic cause.

Atropine and Pacing

Atropine may be attempted for symptomatic bradycardia.

However, it may be ineffective in severe:

• Beta-blocker poisoning
• Calcium-channel blocker poisoning
• Digoxin toxicity

Temporary cardiac pacing may be considered in selected refractory bradyarrhythmias.

A limitation is that pacing can increase the heart rate without correcting severe myocardial contractile failure, so blood pressure may remain poor.

Refractory Toxicologic Shock

When shock remains severe despite conventional treatment, options depend on the toxicant and may include:

• Additional vasopressors
• High-dose insulin
• Specific antidotes
• Intravenous lipid emulsion in selected poisonings
• Extracorporeal toxin removal for appropriate dialyzable substances
• VA-ECMO/mechanical circulatory support for selected potentially reversible poisonings with refractory cardiovascular collapse

Early toxicology and critical-care consultation is important.

Decontamination

Do not induce vomiting.

Routine gastric lavage in hypotensive poisoned patients is not standard modern practice and may create additional risk.

Activated charcoal may be considered after selected ingestions only when:

• Meaningful benefit is expected
• GI function is adequate
• The airway is protected

Resuscitation always takes priority over gastrointestinal decontamination.

Monitoring

Patients with significant toxicologic hypotension require:

• Continuous ECG monitoring
• Frequent blood-pressure assessment
• Serial perfusion examinations
• Glucose monitoring
• Electrolyte and renal-function monitoring
• Assessment of urine output
• Serial lactate when useful

An arterial catheter may be helpful in severe shock requiring titrated vasoactive therapy.

Key Points

• Hypotension is a blood-pressure finding; shock means inadequate tissue perfusion.
• The severity of poisoning should not be judged by blood pressure alone.
• Toxicologic mechanisms include myocardial depression, vasodilation, bradycardia, dysrhythmias, and hypovolemia.
• Bradycardia + hyperglycemia → consider calcium-channel blocker poisoning.
• Bradycardia + CNS depression ± hypoglycemia → consider beta-blocker poisoning.
• Miosis + respiratory depression → consider opioids or clonidine.
• QRS widening + hypotension/seizures → consider sodium-channel blockade, particularly TCAs.
• Acute digoxin poisoning can produce hyperkalemia and dysrhythmias; severe cases require digoxin immune Fab.
• Fluids are useful when hypovolemia is present but excessive volume can worsen drug-induced myocardial failure.
• Norepinephrine is commonly preferred over the older routine dopamine-first approach for persistent shock.
• High-dose insulin therapy is important in severe CCB and beta-blocker poisoning.
• Sodium bicarbonate is central to significant sodium-channel blocker cardiotoxicity.
• Refractory, potentially reversible toxicologic cardiovascular collapse may require VA-ECMO or other advanced circulatory support.

Toxicology – Hyperthermia

Definition

Hyperthermia is an uncontrolled elevation in core body temperature caused by excess heat production, impaired heat dissipation, excessive environmental heat exposure, or a combination of these mechanisms.

It differs from ordinary fever:

• Fever: hypothalamic temperature set point is raised.
• Hyperthermia: temperature rises despite an essentially unchanged hypothalamic set point because heat production exceeds heat loss.

Severe hyperthermia, particularly around ≥40°C with CNS dysfunction, is a medical emergency and can rapidly cause multiorgan injury.

Pathophysiology

Body temperature reflects the balance between heat production and heat dissipation.

Toxicologic hyperthermia may result from:

• Severe agitation or repetitive muscle activity
• Seizures
• Muscle rigidity
• Increased metabolic activity
• Sympathetic stimulation
• Impaired sweating
• Peripheral vasoconstriction
• Environmental heat exposure
• Impaired behavioral responses to heat
• Abnormal thermoregulation

As temperature rises, cellular injury accelerates.

Severe hyperthermia can cause:

Cellular injury → rhabdomyolysis → electrolyte abnormalities → coagulopathy → hepatic/renal injury → cardiovascular collapse → multiorgan failure

Major Toxicologic Causes

Important causes include:

• Sympathomimetic toxicity
• Anticholinergic syndrome
• Serotonin syndrome
• Neuroleptic malignant syndrome (NMS)
• Malignant hyperthermia
• MAOI toxicity
• Salicylate poisoning
• Severe withdrawal syndromes
• Thyroid hormone poisoning
• Drugs causing prolonged seizures

Sympathomimetic Toxicity

Examples include:

• Cocaine
• Amphetamines/methamphetamine
• Methylphenidate
• Other stimulants

Typical findings:

• Hyperthermia
• Agitation
• Tachycardia
• Hypertension
• Mydriasis
• Diaphoresis
• Tremor
• Seizures

Hyperthermia results from increased metabolic activity, agitation, muscle activity, and sometimes impaired heat loss.

Severe cases can produce rhabdomyolysis, hyperkalemia, AKI, DIC, and multiorgan failure.

Anticholinergic Syndrome

Antimuscarinic drugs impair sweating and therefore reduce evaporative cooling.

Typical findings:

• Hyperthermia
• Mydriasis
• Tachycardia
• Dry, flushed skin
• Dry mouth
• Reduced bowel sounds
• Urinary retention
• Delirium/hallucinations

A useful distinction:

Sympathomimetic → hot and sweaty

Anticholinergic → hot and dry

Serotonin Syndrome

Serotonin toxicity commonly causes:

• Hyperthermia
• Agitation
• Diaphoresis
• Tachycardia
• Hypertension
• Hyperreflexia
• Tremor
• Clonus

Severe hyperthermia results largely from excessive muscular activity.

Clonus and hyperreflexia, particularly in the lower extremities, are important clues.

Onset is usually rapid, often within hours of serotonergic drug exposure or interaction.

Neuroleptic Malignant Syndrome

NMS is associated primarily with dopamine-receptor blockade or abrupt withdrawal of dopaminergic therapy.

Features include:

• Hyperthermia
• Altered mental status
• Autonomic instability
• Severe generalized rigidity
• Elevated creatine kinase
• Rhabdomyolysis

Compared with serotonin syndrome:

NMS → slower onset + prominent rigidity/bradykinesia

Serotonin syndrome → rapid onset + hyperreflexia/clonus

Malignant Hyperthermia

Malignant hyperthermia is a genetically susceptible skeletal-muscle hypermetabolic crisis usually triggered by certain volatile anesthetic agents or succinylcholine.

Features can include:

• Rapidly increasing carbon dioxide production
• Tachycardia
• Muscle rigidity
• Acidosis
• Hyperkalemia
• Rhabdomyolysis
• Rapidly increasing temperature

Importantly, hyperthermia may be a relatively late manifestation.

Dantrolene is the specific treatment, together with immediate discontinuation of triggering agents and aggressive supportive management.

MAOI Toxicity

Monoamine oxidase inhibitor poisoning or interactions can produce:

• Agitation
• Hyperthermia
• Hypertension or hypotension
• Altered mental status
• Neuromuscular abnormalities
• Seizures

Severe toxicity may resemble serotonin syndrome or severe sympathomimetic poisoning.

Salicylate Toxicity

Important findings include:

• Hyperthermia
• Tachypnea
• Tinnitus
• Nausea/vomiting
• Altered mental status
• Respiratory alkalosis
• High-anion-gap metabolic acidosis

Hyperthermia is particularly concerning in severe salicylate poisoning.

Withdrawal

Withdrawal from:

• Alcohol
• Benzodiazepines
• Barbiturates and other sedative-hypnotics

can produce a hyperadrenergic state with:

• Agitation
• Tremor
• Diaphoresis
• Tachycardia
• Hypertension
• Hyperthermia
• Seizures

Muscular activity and seizures can further increase heat production.

Seizures and Agitation

Any cause of prolonged:

• Seizures
• Severe agitation
• Rigidity
• Repetitive muscular activity

can generate enough heat to produce dangerous hyperthermia.

Therefore, rapid control of muscular activity is an important component of temperature management.

Nontoxicologic Differential Diagnosis

Consider:

• Environmental heat stroke
• Severe infection/sepsis
• Thyroid storm
• CNS disorders
• Status epilepticus
• Endocrine disease

Heat stroke is especially important.

Classic heat stroke involves:

Core hyperthermia + CNS dysfunction after heat exposure

Sweating may be present or absent, so dry skin is not required for diagnosis.

Clinical Features

Mild cases may cause:

• Thirst
• Weakness
• Tachycardia
• Headache
• Dizziness

Severe hyperthermia can produce:

• Agitation
• Delirium
• Seizures
• Coma
• Hypotension
• Dysrhythmias
• Rhabdomyolysis
• Acute kidney injury
• Hepatic injury
• DIC
• Multiorgan failure

Temperature Measurement

Accurate core temperature measurement is important in severe suspected hyperthermia.

Peripheral measurements such as oral, axillary, or skin temperatures may underestimate the true temperature.

A rectal temperature is commonly used in emergency heat illness because it closely reflects core temperature.

Diagnostic Clues

Hot + sweaty + agitated + mydriatic

→ sympathomimetic toxicity

Hot + dry + delirious + mydriatic

→ anticholinergic syndrome

Hyperthermia + clonus + hyperreflexia

→ serotonin syndrome

Hyperthermia + severe rigidity + dopamine antagonist exposure

→ NMS

Hyperthermia + rigidity + rapidly rising CO₂ during anesthesia

→ malignant hyperthermia

Hyperthermia + tinnitus + tachypnea + acid-base disturbance

→ salicylate toxicity

Laboratory Evaluation

Significant hyperthermia warrants evaluation for systemic complications.

Important tests may include:

• Electrolytes
• Glucose
• Renal function
• Creatine kinase
• Liver enzymes
• Blood gas
• Lactate
• Urinalysis
• Coagulation studies
• ECG

Depending on circumstances:

• Salicylate concentration
• Acetaminophen concentration
• Other targeted toxicology testing

Routine urine drug screening has limited ability to determine the cause and should not delay treatment.

Rhabdomyolysis

Hyperthermia, agitation, seizures, and rigidity can cause extensive skeletal-muscle breakdown.

Findings may include:

• Elevated CK
• Myoglobinuria
• Hyperkalemia
• Hypocalcemia early in the course
• Acute kidney injury

Renal function and electrolytes therefore require close monitoring.

Immediate Management

Severe hyperthermia requires immediate cooling and simultaneous treatment of the underlying cause.

Initial priorities include:

• Airway and ventilation assessment
• Removal from the heat source
• Removal of unnecessary clothing
• IV access
• Cardiac monitoring
• Core-temperature monitoring
• Appropriate IV crystalloid for hypovolemia
• Rapid control of seizures and severe agitation

Cooling should not be delayed while waiting for laboratory results.

External Cooling

Effective approaches depend on the cause and clinical setting.

Methods include:

• Evaporative cooling with water mist and fans
• Ice-water immersion in appropriate heat-stroke settings
• Ice packs as adjuncts
• Other active external cooling techniques

The objective is rapid reduction of dangerous core temperature while avoiding overshoot hypothermia.

Benzodiazepines

Benzodiazepines are particularly useful when hyperthermia is driven by:

• Sympathomimetic toxicity
• Severe agitation
• Seizures
• Alcohol or sedative withdrawal

They reduce muscular activity and sympathetic stimulation, thereby reducing ongoing heat production.

Severe Muscle-Driven Hyperthermia

When extreme hyperthermia persists because of severe agitation, rigidity, or muscular activity despite adequate sedation, advanced airway management and neuromuscular paralysis may be necessary.

This stops skeletal-muscle heat production.

In such circumstances, a nondepolarizing neuromuscular blocker is generally preferred.

Antipyretics

Drugs such as acetaminophen are generally not effective for toxicologic hyperthermia because the problem is not an elevated hypothalamic temperature set point.

Treatment instead requires:

• Physical cooling
• Reduction of muscle activity
• Correction of the underlying toxic syndrome

Syndrome-Specific Treatment

Serotonin syndrome

• Stop serotonergic agents
• Benzodiazepines
• Active cooling
• Cyproheptadine in selected significant cases

NMS

• Stop the causative drug
• Aggressive supportive care and cooling
• Benzodiazepines
• Dantrolene or dopamine agonists in selected severe cases

Malignant hyperthermia

• Stop triggering anesthetic
• Dantrolene
• Aggressive cooling and metabolic management

Salicylate poisoning

• Treat the salicylate toxicity
• Serum/urine alkalinization when indicated
• Hemodialysis for severe poisoning

Fluids

Hyperthermic patients can have major fluid losses from:

• Sweating
• Tachypnea
• Environmental exposure

Isotonic crystalloid is appropriate when hypovolemia is present.

However, fluids should be individualized because excessive administration can worsen pulmonary edema or other complications.

A rigid urine-output target should not replace assessment of overall perfusion, renal function, and volume status.

Decontamination

Do not induce vomiting.

Routine gastric lavage is not recommended for most poisoned patients.

Activated charcoal may be considered after selected recent ingestions when the substance is adsorbed by charcoal and the airway is adequately protected.

Decontamination must never delay rapid cooling and resuscitation in a severely hyperthermic patient.

Prognosis

Mild hyperthermia generally resolves without permanent injury.

Severe hyperthermia can cause:

• Cerebral injury
• Rhabdomyolysis
• Acute kidney injury
• Acute liver failure
• DIC
• ARDS
• Cardiovascular collapse
• Multiorgan failure
• Death

Complications may continue evolving after the temperature has normalized, so patients with severe hyperthermia require continued monitoring.

Key Points

• Hyperthermia is uncontrolled heat accumulation, not simply fever.
• Major toxicologic causes include sympathomimetics, anticholinergics, serotonin syndrome, NMS, malignant hyperthermia, MAOI toxicity, salicylates, and withdrawal syndromes.
• Sympathomimetic = sweaty; anticholinergic = dry.
• Clonus/hyperreflexia → serotonin syndrome.
• Severe rigidity → consider NMS.
• Rapid CO₂ rise and rigidity during anesthesia → malignant hyperthermia.
• Severe hyperthermia can rapidly cause rhabdomyolysis, DIC, hepatic injury, AKI, and multiorgan failure.
• Treatment requires immediate active cooling plus control of agitation, seizures, and muscle activity.
• Antipyretics generally do not treat toxicologic hyperthermia.
• Dantrolene is the specific therapy for malignant hyperthermia.
• Normalization of temperature does not mean the danger has passed; severe cases require continued monitoring for delayed organ injury.

Toxicology – Hyperkalemia

Definition

Hyperkalemia is an abnormally elevated serum potassium concentration, generally >5.0–5.5 mmol/L, depending on the laboratory reference range.

The major danger is disruption of cardiac conduction and neuromuscular function, potentially causing fatal dysrhythmias.

Pathophysiology

Potassium is predominantly intracellular. An increase in extracellular potassium alters the resting membrane potential of excitable cells.

Progressive hyperkalemia causes:

Membrane depolarization → sodium-channel inactivation → impaired conduction → muscle weakness and cardiac conduction abnormalities

Severe hyperkalemia can progress to:

• Bradycardia
• AV block
• Wide-complex rhythms
• Ventricular dysrhythmias
• Cardiac arrest

Major Mechanisms

Hyperkalemia generally results from one or more of four mechanisms:

1. Pseudohyperkalemia

• Hemolysis during blood collection
• Prolonged tourniquet use or fist clenching
• Marked thrombocytosis
• Marked leukocytosis
• Specimen handling problems

2. Reduced renal potassium excretion

• Acute kidney injury
• Chronic kidney disease
• Hypoaldosteronism
• Adrenal insufficiency

3. Potassium shift from cells into plasma

• Acidemia
• Insulin deficiency
• Hyperosmolar states
• Digoxin toxicity
• Extensive tissue injury

4. Increased potassium load

• Potassium supplements
• Excessive IV potassium
• Massive cellular destruction
• Tumor lysis syndrome

Significant potassium intake alone rarely produces severe hyperkalemia when renal function is normal.

Drug-Related Causes

Important medications associated with hyperkalemia include:

• ACE inhibitors
• Angiotensin-receptor blockers
• Potassium-sparing diuretics
• NSAIDs
• Trimethoprim
• Heparin
• Beta-blockers
• Calcineurin inhibitors
• Potassium supplements

Digoxin toxicity is particularly important in toxicology.

Tissue Destruction

Potassium is released from damaged cells.

Causes include:

• Rhabdomyolysis
• Crush injury
• Severe seizures
• Hyperthermia
• Tumor lysis
• Hemolysis

Severe sympathomimetic poisoning can indirectly cause hyperkalemia through hyperthermia, seizures, and rhabdomyolysis.

Digoxin Toxicity

Acute digoxin poisoning can produce significant hyperkalemia because inhibition of the Na⁺/K⁺-ATPase prevents normal cellular potassium uptake.

Associated findings may include:

• Nausea and vomiting
• Bradycardia
• AV block
• Ventricular dysrhythmias
• Visual abnormalities
• Hyperkalemia

In acute digoxin poisoning, hyperkalemia can be an important marker of severe toxicity.

Clinical Features

Mild hyperkalemia may be completely asymptomatic.

Neuromuscular manifestations can include:

• Paresthesias
• Muscle weakness
• Reduced reflexes
• Flaccid paralysis in severe cases

Cardiovascular manifestations include:

• Bradycardia
• Hypotension
• Conduction abnormalities
• Ventricular dysrhythmias
• Cardiac arrest

ECG Changes

Classically described progression includes:

Peaked T waves → PR prolongation → P-wave flattening/loss → QRS widening → sine-wave pattern → ventricular fibrillation/asystole

However, this progression is not reliably sequential.

A patient with severe hyperkalemia may have relatively modest ECG abnormalities, while dangerous dysrhythmias can occasionally develop without the complete classic sequence.

Therefore, neither the ECG nor potassium concentration alone perfectly predicts cardiac risk.

Pseudohyperkalemia

Always consider whether an unexpectedly elevated potassium result is genuine.

Common clues include:

• Laboratory report of hemolysis
• Difficult venipuncture
• Prolonged tourniquet application
• Marked leukocytosis
• Marked thrombocytosis
• No clinical explanation for the result

When the patient is stable and the result is unexpected, potassium can be repeated using a properly collected sample.

Do not delay emergency treatment to repeat the sample when severe hyperkalemia is clinically credible or ECG toxicity is present.

Evaluation

Important initial investigations include:

• Repeat potassium when pseudohyperkalemia is suspected
• Renal function
• Glucose
• Bicarbonate
• Calcium and magnesium
• ECG
• Continuous cardiac monitoring in significant cases

Additional testing depends on the suspected cause:

• Creatine kinase for rhabdomyolysis
• Digoxin concentration
• Blood gas for significant acid-base disturbance
• CBC when marked leukocytosis or thrombocytosis is possible
• Evaluation for adrenal insufficiency when clinically appropriate

Management Principles

Treatment has three major objectives:

1. Stabilize the myocardium

2. Shift potassium into cells

3. Remove potassium from the body

The urgency depends on the overall clinical picture, particularly:

• ECG abnormalities
• Degree and rate of potassium elevation
• Symptoms
• Renal function
• Ongoing potassium release
• Underlying cause

Severe hyperkalemia with cardiac toxicity is a medical emergency.

1. Cardiac Membrane Stabilization

Intravenous calcium is used when significant hyperkalemia is producing concerning ECG abnormalities.

Calcium:

• Stabilizes the cardiac membrane
• Acts rapidly
• Does not lower serum potassium

Its effect is temporary, so potassium-shifting and elimination therapies must also be initiated.

Calcium gluconate and calcium chloride are both used clinically, with calcium chloride delivering more elemental calcium but carrying greater risk of tissue injury if extravasated.

Calcium and Digoxin Toxicity

Older teaching warned that IV calcium in digoxin poisoning could precipitate catastrophic dysrhythmias—the historical “stone heart” concern.

Modern evidence does not support treating calcium as absolutely contraindicated when a patient with suspected digoxin toxicity has life-threatening hyperkalemia.

However, the definitive treatment for severe digoxin poisoning is digoxin immune Fab, and toxicology consultation is appropriate.

2. Shift Potassium Intracellularly

Insulin with glucose

Insulin activates cellular potassium uptake and can rapidly lower extracellular potassium.

The major complication is hypoglycemia, so glucose must be monitored closely for several hours.

Beta₂-adrenergic agonists

Nebulized beta₂ agonists such as albuterol can promote intracellular potassium uptake.

They are generally used as an adjunct rather than the sole treatment for severe hyperkalemia.

Sodium bicarbonate

Bicarbonate is most useful when hyperkalemia occurs with significant metabolic acidosis.

Its potassium-lowering effect is inconsistent in patients without substantial acidemia, so it should not routinely replace insulin or other established therapies.

3. Remove Potassium

Intracellular shifting is temporary. When total-body potassium is excessive, potassium must ultimately be eliminated.

Methods include:

• Renal excretion when kidney function permits
• Potassium-binding agents in appropriate nonemergent settings
• Hemodialysis

Hemodialysis

Hemodialysis provides rapid and reliable potassium removal.

It is particularly important when there is:

• Severe hyperkalemia with kidney failure
• Refractory hyperkalemia
• Recurrent hyperkalemia despite temporizing treatment
• Severe ongoing potassium release
• Inadequate renal elimination

Emergency membrane stabilization and intracellular shifting should not be delayed while dialysis is being arranged.

Potassium-Binding Resins

The source emphasizes sodium polystyrene sulfonate (SPS/Kayexalate), but its role has changed substantially.

SPS:

• Has a delayed and somewhat unpredictable effect
• Is not appropriate as the sole emergency treatment for life-threatening hyperkalemia
• Can cause significant gastrointestinal adverse effects

Use with sorbitol is particularly problematic because of an association with serious intestinal injury.

Newer potassium binders have roles in selected patients, especially chronic hyperkalemia, but they do not replace immediate cardiac stabilization and rapid potassium-shifting therapy in an unstable patient.

Digoxin-Associated Hyperkalemia

When severe acute digoxin poisoning is responsible:

Digoxin immune Fab is the definitive antidotal treatment.

Fab binds circulating digoxin and reverses inhibition of Na⁺/K⁺-ATPase.

As toxicity reverses, extracellular potassium can move back into cells, so potassium may fall rapidly.

Serial potassium monitoring is therefore essential.

Monitoring

Significant hyperkalemia requires:

• Continuous cardiac monitoring
• Serial ECGs when appropriate
• Serial potassium measurements
• Glucose monitoring after insulin therapy
• Renal-function monitoring

Also identify whether potassium is continuing to enter the circulation from:

• Rhabdomyolysis
• Tumor lysis
• Tissue ischemia
• Ongoing potassium administration

Key Points

• Hyperkalemia can cause rapidly fatal cardiac conduction abnormalities.
• Major mechanisms are reduced renal excretion, intracellular-to-extracellular shifting, increased potassium load, and pseudohyperkalemia.
• Always consider pseudohyperkalemia, particularly with a hemolyzed specimen or unexpected result.
• Do not delay treatment to repeat the potassium when severe hyperkalemia and cardiac toxicity are clinically credible.
• ECG changes classically progress from peaked T waves to QRS widening and a sine-wave pattern, but actual progression is unpredictable.
• Emergency management follows three principles: stabilize the heart → shift K⁺ into cells → remove K⁺ from the body.
• IV calcium stabilizes the myocardium but does not lower potassium.
• Insulin promotes intracellular potassium uptake; monitor carefully for hypoglycemia.
• Bicarbonate is most useful when significant metabolic acidosis accompanies hyperkalemia.
• Hemodialysis is highly effective for severe or refractory hyperkalemia, particularly with renal failure.
• Sodium polystyrene sulfonate is not an adequate emergency treatment, and routine administration with sorbitol is no longer favored.
• Acute digoxin poisoning can cause hyperkalemia through Na⁺/K⁺-ATPase inhibition; severe toxicity is treated with digoxin immune Fab.