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 – Hearing Abnormalities

Definition

Toxic exposures and medications can produce auditory abnormalities, most commonly:

• Tinnitus – perception of ringing, buzzing, or other sound without an external source
• Hearing loss – partial or complete reduction in hearing

Drug-induced hearing loss is usually sensorineural, although conductive and central auditory disorders have other important causes.

Normal Hearing

Sound transmission occurs through:

Sound waves → tympanic membrane → ossicles → cochlear fluid movement → organ of Corti hair cells → cochlear nerve (CN VIII) → auditory cortex

Damage anywhere along this pathway can impair hearing.

Conductive vs. Sensorineural Hearing Loss

Conductive hearing loss

Results from impaired transmission through the:

• External auditory canal
• Tympanic membrane
• Middle ear

Examples include:

• Cerumen impaction
• Foreign body
• Otitis media
• Tympanic membrane injury
• Otosclerosis

Sensorineural hearing loss

Results from injury to:

• Cochlear hair cells
• Stria vascularis
• Cochlear nerve
• Central auditory pathways

Potential causes include:

• Ototoxic medications
• Excessive noise exposure
• Infection
• Aging
• Vascular disease
• Temporal bone injury
• Vestibular schwannoma
• Toxic chemical exposure

Major Ototoxic Drugs

Important medications associated with tinnitus or hearing impairment include:

Aminoglycosides

• Gentamicin
• Tobramycin
• Amikacin
• Streptomycin
• Neomycin

These can produce cochlear and/or vestibular toxicity.

Risk increases with:

• Higher cumulative exposure
• Renal dysfunction
• Concurrent ototoxic medications

Hearing injury can be irreversible.

Platinum Chemotherapy

Cisplatin is an important cause of:

• Bilateral sensorineural hearing loss
• High-frequency hearing impairment
• Tinnitus

Ototoxicity may be cumulative and permanent.

Salicylates

Salicylate toxicity commonly causes:

• Tinnitus
• Reduced hearing
• Nausea/vomiting
• Tachypnea
• Acid-base abnormalities

The auditory abnormalities are generally reversible after salicylate concentrations fall.

Key Point: Improvement or disappearance of tinnitus does not reliably prove that systemic salicylate toxicity has resolved.

Quinine and Quinidine

These may produce cinchonism, characterized by:

• Tinnitus
• Hearing impairment
• Headache
• Nausea
• Visual disturbances

Severe poisoning can additionally cause cardiovascular toxicity.

Loop Diuretics

Examples include:

• Furosemide
• Bumetanide
• Ethacrynic acid

Ototoxicity is particularly associated with:

• Rapid IV administration
• High exposure
• Renal dysfunction
• Concurrent ototoxic medications

Hearing impairment is often reversible but can occasionally persist.

Other Potentially Ototoxic Agents

Reported associations include:

• Macrolide antibiotics
• Chloroquine and related agents
• Deferoxamine
• Some NSAIDs
• Metronidazole
• Selected local anesthetics
• Certain industrial solvents
• Heavy metals

Not every reported association carries the same strength of evidence or risk.

Toxic Chemical Causes

Organic mercury

May produce:

• Hearing impairment
• Visual-field abnormalities
• Ataxia
• Dysarthria
• Tremor
• Sensory disturbances

Lead

Chronic exposure can produce neurologic abnormalities and has been associated with auditory dysfunction, particularly with significant or prolonged exposure.

Solvents

Some occupational solvents, including toluene, can contribute to sensorineural hearing impairment, particularly with chronic exposure and concurrent noise exposure.

Carbon Monoxide and Cyanide

Severe cellular hypoxia can injure auditory pathways.

Hearing abnormalities have occasionally been reported following recovery from severe:

• Carbon monoxide poisoning
• Cyanide poisoning

In these cases, auditory injury may become apparent after the initial life-threatening toxicity has resolved.

Bromate

Significant bromate poisoning can produce:

• Vomiting and diarrhea
• Acute kidney injury
• Sensorineural hearing loss

Hearing impairment may be permanent.

Clinical Assessment

Important history includes:

• Onset: sudden vs. gradual
• Unilateral vs. bilateral symptoms
• Tinnitus vs. hearing loss
• Medication exposure
• Recent overdose
• Occupational chemical exposure
• Noise exposure
• Renal impairment
• Ear infection or trauma
• Associated vestibular symptoms

Medication review is particularly important because multiple ototoxic drugs may have additive effects.

Associated Findings

Certain combinations provide diagnostic clues.

Tinnitus + tachypnea + vomiting + acid-base disturbance

→ consider salicylate toxicity

Hearing loss + renal injury during antimicrobial treatment

→ consider aminoglycoside toxicity

Hearing loss during cisplatin therapy

→ consider platinum-associated ototoxicity

Tinnitus + visual disturbances

→ consider quinine/quinidine toxicity

Hearing impairment + ataxia/tremor/visual abnormalities

→ consider organic mercury exposure

Physical Examination

Assess:

• External auditory canal
• Tympanic membrane
• Evidence of infection
• Cerumen or foreign body
• Neurologic examination
• Cranial nerves
• Vestibular findings when relevant

Bedside hearing tests can help distinguish conductive from sensorineural loss.

Weber Test

A vibrating tuning fork is placed on the midline of the skull.

Normal

• Sound is heard approximately equally in both ears.

Unilateral conductive hearing loss

• Sound lateralizes toward the affected ear.

Unilateral sensorineural hearing loss

• Sound lateralizes toward the better/unaffected ear.

Rinne Test

The test compares air conduction (AC) with bone conduction (BC).

Normally:

AC > BC

Conductive hearing loss

• Bone conduction becomes greater than air conduction in the affected ear.

Sensorineural hearing loss

• Air conduction generally remains greater than bone conduction, but overall hearing is reduced.

A 512-Hz tuning fork is generally preferred for modern bedside Weber and Rinne testing rather than the 256-Hz fork described in older references.

Audiologic Evaluation

Formal assessment may include:

• Pure-tone audiometry
• Speech audiometry
• Tympanometry
• Otoacoustic emissions
• Auditory brainstem response testing

Audiometry is especially useful for detecting and monitoring medication-associated ototoxicity.

Laboratory Evaluation

Testing should be directed toward the suspected cause.

Possible investigations include:

• Renal function
• Electrolytes
• Salicylate concentration
• Specific medication concentrations when clinically useful
• Heavy-metal testing when exposure is plausible
• Acid-base evaluation in systemic poisoning

Routine broad toxicology screening is usually less useful than targeted testing.

Imaging

Imaging is determined by the clinical pattern.

Unilateral or asymmetric sensorineural hearing loss

may warrant MRI evaluation for retrocochlear pathology such as a vestibular schwannoma.

Temporal-bone imaging may be appropriate when trauma or structural disease is suspected.

Sudden Sensorineural Hearing Loss

Sudden unexplained sensorineural hearing loss should be considered an otologic emergency.

Prompt ENT/audiology evaluation is important because time-sensitive treatment may be indicated for causes unrelated to poisoning.

Do not automatically attribute sudden hearing loss to a medication merely because the patient is taking a potentially ototoxic drug.

Management

Management centers on the underlying cause:

• Stop or modify the suspected ototoxic agent when medically appropriate.
• Treat the underlying poisoning.
• Correct renal or metabolic abnormalities.
• Avoid additional ototoxic exposures when possible.
• Obtain audiology/ENT assessment for persistent or significant abnormalities.

Medication changes should account for the clinical importance of the original treatment; an essential antimicrobial or chemotherapy agent should not simply be discontinued without appropriate specialist input.

Decontamination

Management depends on the route and specific toxicant.

For inhalational exposure:

• Remove the patient from the source.
• Provide appropriate supportive care.

For dermal contamination:

• Remove contaminated clothing when appropriate.
• Irrigate exposed skin according to the chemical involved.

Historical recommendations for routine ipecac or gastric lavage after ingestion are not part of standard modern management.

Prognosis

Recovery depends on the agent and extent of cochlear injury.

Often reversible:

• Salicylate-associated tinnitus/hearing impairment
• Many NSAID-related auditory effects
• Some loop-diuretic-associated hearing abnormalities

Potentially permanent:

• Aminoglycoside ototoxicity
• Cisplatin ototoxicity
• Bromate-associated hearing loss
• Severe cochlear injury from other toxicants

Key Points

• Toxicants most commonly produce sensorineural hearing abnormalities.
• Major ototoxic agents include aminoglycosides, cisplatin, salicylates, quinine/quinidine, and loop diuretics.
• Tinnitus is a classic manifestation of salicylate toxicity, but its disappearance does not prove that the poisoning has resolved.
• Aminoglycoside toxicity is more likely with renal dysfunction and greater cumulative exposure.
• Cisplatin commonly affects high-frequency hearing and may cause permanent injury.
• Weber and Rinne tests help distinguish conductive from sensorineural hearing loss.
• Weber: conductive → affected ear; sensorineural → unaffected ear.
• Rinne: normal/sensorineural = AC > BC; conductive = BC > AC.
• Sudden unexplained sensorineural hearing loss requires prompt specialist evaluation.
• Treatment primarily involves recognizing the responsible agent, treating systemic toxicity, and preventing further ototoxic exposure.

Toxicology – Gulf War Illness

Definition

Gulf War illness (GWI), historically called Gulf War syndrome, is a chronic multisymptom illness occurring in a subset of military personnel who served in the 1990–1991 Persian Gulf War.

Common manifestations involve several systems and include:

• Persistent fatigue
• Cognitive or memory difficulties
• Headache
• Muscle and joint pain
• Sleep disturbance
• Gastrointestinal symptoms
• Respiratory complaints
• Skin symptoms

Modern literature generally prefers the term Gulf War illness because affected veterans have recognizable patterns of chronic symptoms even though there is no single diagnostic laboratory test or universally established mechanism.

Pathophysiology

The pathophysiology remains incompletely understood.

Research has investigated several potentially interacting mechanisms, including:

• Neuroinflammation
• Autonomic nervous system abnormalities
• Immune dysregulation
• Mitochondrial dysfunction
• Neuroendocrine alterations
• Genetic susceptibility interacting with deployment exposures

No single mechanism currently explains every case.

Potential Deployment-Related Exposures

Gulf War personnel encountered a complex mixture of environmental and occupational exposures.

Investigated possibilities include:

• Organophosphate and other pesticides
• Pyridostigmine bromide
• Low-level nerve-agent exposure in some personnel
• Oil-well fire smoke
• Petroleum products and solvents
• Depleted uranium
• Chemical-agent-resistant coatings
• Vaccinations
• Dust and particulate matter
• Psychological and physiologic stress

Evidence supporting a causal relationship is not equally strong for all of these exposures.

Pesticides

Pesticides are among the deployment exposures that have received substantial attention.

Agents used during deployment included various:

• Organophosphate insecticides
• Carbamates
• Pyrethroids
• Insect repellents such as DEET

Organophosphates inhibit acetylcholinesterase and can produce acute cholinergic toxicity at sufficiently high exposure.

Importantly, the absence of an obvious acute cholinergic crisis does not by itself exclude lower-level exposure or establish whether such exposure contributed to later Gulf War illness.

Pyridostigmine Bromide

Pyridostigmine was provided to some Gulf War personnel as a pretreatment intended for use in anticipation of possible nerve-agent exposure.

It reversibly inhibits acetylcholinesterase.

Acute adverse effects can include:

• Abdominal cramping
• Diarrhea
• Increased secretions
• Sweating
• Other cholinergic manifestations

Research has examined whether pyridostigmine, particularly in combination with other deployment exposures, contributed to GWI. This remains an area of scientific investigation rather than a simple single-agent explanation.

Nerve Agents

Possible exposure to organophosphate nerve agents has been extensively investigated.

A particularly important historical event was the 1991 demolition of Iraqi munitions at Khamisiyah, during which some U.S. personnel may have been exposed to low levels of sarin/cyclosarin released into the atmosphere.

High-dose nerve-agent poisoning produces an acute cholinergic syndrome with:

• Miosis
• Bronchorrhea
• Salivation
• Vomiting and diarrhea
• Fasciculations
• Weakness
• Seizures
• Respiratory failure

The relationship between lower-level wartime exposure and chronic Gulf War illness has been the subject of continuing epidemiologic research.

Oil-Well Fires and Combustion Products

Burning Kuwaiti oil wells generated substantial smoke and particulate pollution.

Potential exposures included:

• Particulate matter
• Hydrocarbons
• Carbon monoxide
• Sulfur compounds
• Nitrogen oxides
• Other combustion products

These exposures can produce acute:

• Eye and mucosal irritation
• Cough
• Bronchial irritation
• Exacerbation of underlying respiratory disease

Their contribution to the overall chronic multisymptom illness remains less clearly established than some other proposed exposures.

Depleted Uranium

Depleted uranium exposure occurred particularly among personnel involved with:

• Friendly-fire incidents
• Damaged armored vehicles
• Depleted-uranium munitions

Uranium has both chemical toxicity and weak radioactivity, with the kidney being an important target of sufficiently large systemic exposure.

Research has not established depleted uranium as a general explanation for the broad pattern of Gulf War illness across affected veterans.

Chemical-Agent-Resistant Coatings

Some military equipment was treated with chemical-resistant coatings containing compounds capable of causing occupational toxicity.

Isocyanates, for example, can cause:

• Airway irritation
• Occupational asthma
• Respiratory sensitization

Such exposures may explain particular respiratory problems in exposed individuals but do not by themselves account for the overall GWI syndrome.

Vaccinations

Personnel received multiple vaccines associated with deployment requirements.

Vaccination-related hypotheses have been investigated, but vaccines have not been established as a single general cause of Gulf War illness.

Psychological Stress and PTSD

Combat and deployment stress can produce:

• PTSD
• Anxiety
• Depression
• Sleep disturbance
• Cognitive symptoms
• Physical symptoms

However, Gulf War illness should not simply be equated with PTSD or considered purely psychological.

GWI and PTSD are distinct conditions, although they may coexist in the same individual.

Clinical Features

GWI typically involves symptoms across multiple domains.

Neurologic/Cognitive

• Headache
• Memory difficulties
• Problems with concentration
• Cognitive complaints

General

• Persistent fatigue
• Reduced exercise tolerance

Musculoskeletal

• Muscle pain
• Joint pain

Sleep

• Poor-quality sleep
• Insomnia or other sleep disturbance

Gastrointestinal

• Abdominal symptoms
• Diarrhea
• Other chronic GI complaints

Respiratory

• Cough
• Shortness of breath
• Other respiratory complaints

Dermatologic

• Recurrent or persistent skin symptoms

The exact combination and severity vary considerably between individuals.

Diagnosis

There is no single diagnostic biomarker or laboratory test that confirms Gulf War illness.

Diagnosis is based on:

• Gulf War deployment history
• Characteristic chronic multisystem symptoms
• Duration and functional impact
• Exclusion or identification of alternative explanations

Research and clinical frameworks use symptom-based criteria, including the CDC chronic multisymptom illness definition and the Kansas Gulf War illness criteria.

Differential Diagnosis

Because GWI symptoms are nonspecific, other treatable conditions should be considered rather than attributing every symptom automatically to deployment.

Depending on presentation, alternatives include:

• Thyroid disease
• Anemia
• Sleep disorders
• Chronic infection
• Autoimmune disease
• Neurologic disorders
• Medication adverse effects
• Fibromyalgia
• Chronic fatigue syndromes
• PTSD, depression, or anxiety disorders

These diagnoses may also coexist with GWI.

Laboratory Testing

No characteristic routine laboratory abnormality defines GWI.

Testing should therefore be directed by:

• Symptoms
• Physical examination
• Exposure history
• Relevant differential diagnoses

Broad indiscriminate toxicology testing decades after deployment generally cannot reconstruct historical exposures.

Management

There is no single established antidote or universally effective disease-specific treatment.

Management is individualized and generally focuses on:

• Treating specific symptoms
• Managing sleep disorders
• Addressing chronic pain
• Treating gastrointestinal or respiratory disease when identified
• Physical rehabilitation appropriate to tolerance
• Management of coexisting medical or psychological conditions
• Ongoing clinical follow-up

Treatment should focus on improving function and quality of life while avoiding the assumption that every new symptom necessarily results from GWI.

Decontamination

There is no role for decontamination because the relevant deployment exposures occurred decades ago.

Similarly, empiric chelation or other attempts to remove presumed historical toxicants are not routinely indicated without evidence of a current specific toxic exposure.

Prognosis

The course varies.

Some individuals improve, whereas others experience persistent symptoms lasting many years.

Because GWI is heterogeneous, prognosis depends partly on:

• Symptom pattern
• Severity
• Functional impairment
• Coexisting conditions

Key Points

• Gulf War illness is a chronic multisymptom illness affecting a subset of 1990–1991 Gulf War veterans.
• Common manifestations include fatigue, cognitive problems, musculoskeletal pain, headache, sleep disturbance, and GI symptoms.
• The pathophysiology remains incompletely understood and is probably more complex than exposure to a single toxicant.
• Investigated exposures include pesticides, pyridostigmine bromide, nerve agents, oil-well fire smoke, depleted uranium, and other deployment-related exposures.
• Some personnel may have experienced low-level nerve-agent exposure associated with the Khamisiyah demolitions.
• GWI should not be dismissed as simply PTSD or psychological illness, although PTSD and other psychiatric conditions can coexist.
• There is no single confirmatory laboratory test or biomarker.
• Diagnosis is clinical and requires consideration of other treatable diseases.
• No specific antidote exists; treatment is primarily individualized symptom management and rehabilitation.
• Historical exposure does not justify current decontamination or empiric chelation.

Toxicology – Coma

Definition

Coma is a state of profoundly depressed consciousness in which the patient cannot be appropriately aroused or respond meaningfully to external stimuli.

In toxicology, coma is a clinical syndrome rather than a diagnosis. The immediate priorities are to identify and treat reversible threats to oxygenation, ventilation, circulation, and cerebral metabolism.

Pathophysiology

Major mechanisms that can produce coma include:

• CNS-depressant drugs or toxins
• Hypoxia or inadequate cerebral perfusion
• Hypoglycemia
• Severe electrolyte disturbances
• Acid-base abnormalities
• Hyperthermia or hypothermia
• Structural intracranial disease
• Seizures or postictal states
• Severe systemic infection or metabolic disease

Many different poisons can eventually cause coma, particularly as a preterminal manifestation.

Important Toxicologic Causes

Opioids

• CNS depression
• Respiratory depression
• Miosis
• Reduced bowel sounds

The most immediately dangerous manifestation is hypoventilation.

Sedative-hypnotics

Examples include:

• Benzodiazepines
• Barbiturates
• Ethanol
• Other CNS depressants

Typical findings include:

• Somnolence progressing to coma
• Ataxia before severe CNS depression
• Respiratory depression in severe poisoning

Isolated benzodiazepine overdose usually causes less respiratory depression than combinations with opioids, ethanol, or other sedatives.

Clonidine and imidazolines

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

These can mimic opioid poisoning.

Tricyclic antidepressants

Severe toxicity may produce:

• Coma
• Seizures
• Hypotension
• Tachycardia
• QRS widening
• Ventricular dysrhythmias

Anticonvulsants

Many cause:

• Nystagmus
• Ataxia
• Slurred speech
• CNS depression

Severe poisoning can progress to coma.

Cellular Asphyxiants and Toxic Gases

Carbon monoxide

• Headache
• Nausea
• Confusion
• Syncope
• Coma in severe poisoning

Pulse oximetry may appear misleadingly normal.

Cyanide

• Rapid neurologic deterioration
• Cardiovascular collapse
• Severe lactic acidosis

Hydrogen sulfide

• Rapid collapse after major exposure
• Respiratory failure
• Seizures or coma

Multiple simultaneously affected patients can be an important environmental clue.

Toxic Alcohols

Methanol

Early intoxication may resemble ethanol exposure.

Later findings include:

• High-anion-gap metabolic acidosis
• Visual abnormalities
• CNS depression
• Coma

Ethylene glycol

Later toxicity may include:

• High-anion-gap metabolic acidosis
• Hypocalcemia
• Acute kidney injury
• CNS depression

Isopropanol

Typically produces:

• Marked CNS depression
• Ketosis
• GI irritation or hemorrhagic gastritis

Unlike methanol and ethylene glycol, isopropanol classically produces ketosis without a high-anion-gap metabolic acidosis attributable to toxic metabolites.

Clinical Examination

The physical examination should look for a recognizable toxidrome.

Important features include:

• Vital signs
• Respiratory pattern
• Pupils
• Skin temperature and moisture
• Bowel sounds
• Muscle tone
• Reflexes
• Clonus or rigidity
• Evidence of trauma
• Focal neurologic abnormalities

Pupillary Clues

Miosis

• Opioids
• Clonidine/imidazolines
• Cholinergic poisoning

Mydriasis

• Sympathomimetics
• Antimuscarinic agents
• Severe hypoxia
• Some antidepressants and anticonvulsants

Nystagmus

May occur with:

• Ethanol
• Phenytoin
• Carbamazepine
• Sedative-hypnotics
• Dissociative agents such as PCP

Pupil findings are supportive but not diagnostic by themselves.

Vital-Sign Clues

Tachycardia

• Sympathomimetics
• Antimuscarinics
• TCAs and other sodium-channel blockers

Bradycardia

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

Hyperthermia

• Sympathomimetic toxicity
• Anticholinergic syndrome
• Serotonin syndrome
• Neuroleptic malignant syndrome
• Severe salicylate poisoning

Hypothermia

• Sedative intoxication
• Environmental exposure during prolonged unconsciousness

Respiratory Pattern

Bradypnea/hypoventilation

suggests:

• Opioids
• Sedative-hypnotics
• Clonidine
• Severe CNS depression

Tachypnea/hyperpnea

may occur with:

• Salicylates
• Methanol
• Ethylene glycol
• Metabolic acidosis
• Hypoxia
• Hyperthermia

Respiratory pattern can therefore provide an important clue to the underlying poison.

ECG

An ECG should be obtained early in unexplained toxicologic coma.

Important abnormalities include:

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

QRS widening with a prominent terminal R wave in aVR can support significant cardiac sodium-channel blockade, classically associated with TCA poisoning, although it is not specific to TCAs.

Laboratory Evaluation

Immediate evaluation commonly includes:

• Bedside glucose
• Electrolytes
• Bicarbonate
• Renal function
• Calcium and magnesium
• ECG
• Oxygenation and ventilation assessment

Depending on circumstances:

• Blood gas
• Serum acetaminophen concentration
• Salicylate concentration
• Ethanol concentration
• Toxic alcohol evaluation
• Specific drug concentrations
• Creatine kinase
• Liver tests

An unexplained high-anion-gap metabolic acidosis should prompt consideration of toxic and nontoxic causes, including toxic alcohols, salicylates, lactic acidosis, and other metabolic disorders.

Urine Drug Screening

Routine urine immunoassay drug screens have important limitations.

A positive result:

• Does not establish current intoxication.
• Does not prove the detected drug caused the coma.

A negative result:

• Does not exclude poisoning.
• May miss many clinically important substances.

Management should therefore be based primarily on the clinical syndrome and targeted testing.

Structural and Nontoxicologic Causes

Do not automatically assume that an unconscious patient is poisoned.

Important alternatives include:

• Intracranial hemorrhage
• Ischemic stroke
• CNS infection
• Seizure/postictal state
• Hypoglycemia
• Severe sodium abnormalities
• Sepsis
• Hepatic or uremic encephalopathy

Focal neurologic abnormalities increase concern for structural CNS disease, but their absence does not completely exclude an intracranial process.

Brain imaging, lumbar puncture, cultures, or other investigations may therefore be necessary depending on the presentation.

Initial Management

Management follows standard resuscitation priorities:

• Ensure airway patency.
• Assess breathing and ventilation.
• Provide oxygen when indicated.
• Assist ventilation when inadequate.
• Establish IV access.
• Monitor cardiac rhythm and vital signs.
• Check bedside glucose immediately.
• Treat seizures and major temperature abnormalities.

Endotracheal intubation is indicated when the patient cannot maintain adequate ventilation or reliably protect the airway.

Naloxone

Naloxone should be given when opioid-induced respiratory depression is suspected.

The goal is restoration of:

• Adequate ventilation
• Adequate airway protection

Complete awakening is not required.

Routine naloxone solely because a patient is unconscious is less useful when there is no evidence of opioid-related respiratory depression.

Glucose and Thiamine

Glucose

Check bedside glucose promptly and treat documented or strongly suspected hypoglycemia immediately.

The older practice of automatically giving concentrated dextrose to every comatose patient has largely been replaced by rapid point-of-care glucose testing.

Thiamine

Thiamine is appropriate when deficiency is suspected, particularly in patients with malnutrition or chronic heavy alcohol use.

When hypoglycemia is present, glucose treatment should not be delayed while waiting to administer thiamine.

Flumazenil

Flumazenil reverses benzodiazepine effects but is not routinely recommended for undifferentiated overdose-associated coma.

It can precipitate seizures or withdrawal, particularly in:

• Chronic benzodiazepine users
• Patients with seizure disorders
• Mixed overdoses
• Coingestion of proconvulsant drugs such as TCAs

Its use is therefore generally restricted to carefully selected circumstances.

Decontamination

Do not induce vomiting in a patient with depressed consciousness.

Older recommendations for routine gastric lavage in comatose overdose patients are obsolete and potentially dangerous.

Activated charcoal may occasionally be appropriate after selected ingestions, but it should not be administered to a patient with impaired airway reflexes unless the airway is adequately protected and the expected benefit justifies its use.

Complications

Important complications of prolonged coma include:

• Aspiration
• Hypoxic brain injury
• Pressure injury
• Rhabdomyolysis
• Acute kidney injury
• Hypothermia
• Venous thromboembolism
• Respiratory failure

Drug Intoxication and Brain Death Assessment

Profound intoxication with certain CNS depressants can closely mimic catastrophic neurologic injury.

Therefore, drug intoxication and other reversible confounders must be adequately excluded before determination of death by neurologic criteria.

An EEG alone is not sufficient to resolve this issue in a deeply intoxicated patient.

Key Points

• Coma is a syndrome, not a diagnosis.
• Stabilize airway, breathing, circulation, and glucose while investigating the cause.
• Miosis + respiratory depression → strongly consider opioids, but clonidine and cholinergic poisoning can mimic this pattern.
• QRS widening + coma/seizures/hypotension → consider sodium-channel-blocking toxicity, including TCAs.
• High-anion-gap metabolic acidosis can provide an important clue to toxic alcohols, salicylates, cyanide-related lactic acidosis, and other toxic/metabolic disorders.
• Naloxone is primarily used to reverse suspected opioid-induced respiratory depression, not simply unconsciousness.
• Flumazenil should not routinely be used in undifferentiated overdose coma.
• Routine urine drug screens cannot reliably identify or exclude the cause of coma.
• Routine gastric lavage in poisoned comatose patients is obsolete.
• Always consider structural neurologic, infectious, metabolic, and toxicologic causes simultaneously.

Toxicology – Cholinergic Syndrome

Definition

Cholinergic syndrome is a toxidrome caused by excessive stimulation of acetylcholine receptors.

The classic syndrome includes:

• Excessive salivation and lacrimation
• Sweating
• Bronchorrhea and bronchospasm
• Miosis
• Vomiting and diarrhea
• Urination
• Bradycardia

Severe poisoning may additionally cause:

• Fasciculations
• Muscle weakness or paralysis
• Altered mental status
• Seizures
• Respiratory failure

Pathophysiology

Many important cholinergic poisons inhibit acetylcholinesterase (AChE), the enzyme responsible for breaking down acetylcholine.

This produces:

AChE inhibition → acetylcholine accumulation → excessive muscarinic + nicotinic + CNS stimulation

The two major peripheral receptor groups produce different manifestations.

Muscarinic Effects

Muscarinic overstimulation produces:

• Miosis
• Salivation
• Lacrimation
• Sweating
• Bronchorrhea
• Bronchospasm
• Bradycardia
• Vomiting
• Abdominal cramping
• Diarrhea
• Urination

A useful mnemonic is DUMBELS:

• D – Defecation/Diarrhea, Diaphoresis
• U – Urination
• M – Miosis
• B – Bronchorrhea, Bronchospasm, Bradycardia
• E – Emesis
• L – Lacrimation
• S – Salivation

Nicotinic Effects

Nicotinic receptor overstimulation at autonomic ganglia and the neuromuscular junction can cause:

• Muscle fasciculations
• Muscle weakness
• Paralysis
• Tachycardia
• Hypertension

Severe neuromuscular weakness can contribute substantially to respiratory failure.

Central Nervous System Effects

Because some cholinesterase inhibitors enter the CNS, severe poisoning may cause:

• Anxiety or agitation
• Confusion
• Altered consciousness
• Seizures
• Coma
• Central respiratory depression

Organophosphates

Organophosphate insecticides are major causes of severe cholinergic poisoning.

They inhibit acetylcholinesterase by phosphorylating the enzyme.

Over time, the organophosphate–AChE complex can undergo “aging,” after which reactivation of the enzyme becomes increasingly difficult.

Recovery then depends substantially on synthesis of new functional enzyme.

Carbamates

Carbamates also inhibit acetylcholinesterase but generally form a reversible carbamylated enzyme complex.

Their toxicity is often shorter-lived than organophosphate poisoning, although severe poisoning can still occur.

Other Causes

Cholinergic manifestations can also occur with:

• Physostigmine
• Neostigmine
• Pyridostigmine
• Bethanechol
• Pilocarpine
• Certain muscarine-containing mushrooms
• Nicotine and related agents, although their receptor effects differ from classic AChE inhibition

Not every cholinergic syndrome is therefore caused by an organophosphate.

Clinical Features

Eyes/HEENT

• Miosis
• Lacrimation
• Salivation
• Blurred vision

Skin

• Profuse sweating

Cardiovascular

• Bradycardia from muscarinic activity
• Tachycardia and hypertension from nicotinic ganglionic activity
• Hypotension
• Dysrhythmias in severe poisoning

The heart rate can therefore be either slow or fast.

Gastrointestinal

• Nausea
• Vomiting
• Abdominal cramping
• Diarrhea
• Increased bowel activity

Neuromuscular

• Fasciculations
• Weakness
• Paralysis

Neurologic

• Confusion
• Seizures
• CNS depression
• Coma

Respiratory Failure

Respiratory compromise is the major immediate threat.

It may result simultaneously from:

• Bronchorrhea
• Bronchospasm
• Central respiratory depression
• Neuromuscular weakness/paralysis
• Aspiration
• Pulmonary edema in severe cases

This combination can cause rapid hypoxemia and respiratory arrest.

Differential Diagnosis

Conditions that can partially resemble cholinergic poisoning include:

Nicotine toxicity

• Nausea/vomiting
• Sweating
• Fasciculations
• Autonomic instability

Opioid poisoning

• Miosis and respiratory depression, but usually without profuse secretions or fasciculations

Sympathomimetic poisoning

• Sweating, tachycardia, hypertension and agitation, but usually mydriasis rather than miosis and without the characteristic bronchorrhea

Beta-blocker, calcium-channel blocker, or digoxin toxicity

• Can cause bradycardia and hypotension but generally lack the characteristic secretory syndrome.

Botulism

• Produces weakness/paralysis but typically causes dryness and descending paralysis, rather than a wet cholinergic syndrome.

Diagnosis

Diagnosis is primarily clinical.

The combination of:

miosis + profuse secretions + bronchorrhea + fasciculations/weakness

strongly suggests significant cholinergic poisoning.

Exposure history should include:

• Pesticides
• Occupational exposure
• Medications
• Plants or mushrooms
• Possible dermal or inhalational exposure

Cholinesterase Testing

Laboratory measurements may include:

Plasma butyrylcholinesterase

• Often readily available
• Sensitive to exposure
• Less closely related to neuromuscular AChE activity

Red blood cell acetylcholinesterase

• More closely reflects neuronal/neuromuscular acetylcholinesterase activity
• May correlate better with significant organophosphate effects

However, treatment of a severely symptomatic patient should not wait for cholinesterase results.

Additional Evaluation

Depending on severity:

• ECG and continuous cardiac monitoring
• Oxygen saturation
• Blood gas when respiratory failure is suspected
• Electrolytes
• Glucose
• Renal function
• Chest imaging when pulmonary complications are suspected

Management

Immediate priorities are:

• Airway management
• Oxygenation and ventilation
• Suctioning of excessive secretions
• Cardiac monitoring
• Treatment of seizures
• Removal from ongoing exposure

Severe poisoning may require early endotracheal intubation and mechanical ventilation.

Decontamination

For significant dermal contamination:

• Remove contaminated clothing.
• Prevent secondary contamination of healthcare personnel.
• Thoroughly wash exposed skin.

Ocular exposures require irrigation.

Do not induce vomiting.

Older recommendations for routine gastric lavage are no longer standard practice.

Activated charcoal may be considered after selected ingestions when clinically appropriate and when the airway can be safely protected.

Atropine

Atropine is a competitive muscarinic acetylcholine receptor antagonist.

It treats the life-threatening muscarinic manifestations, particularly:

• Bronchorrhea
• Bronchospasm
• Bradycardia

The major therapeutic endpoint in severe poisoning is improvement in pulmonary secretions and ventilation, rather than normalization of pupil size or heart rate.

Severe organophosphate poisoning can require very large cumulative amounts of atropine.

Importantly, atropine does not directly reverse nicotinic neuromuscular weakness.

Pralidoxime (2-PAM)

Pralidoxime is an oxime cholinesterase reactivator.

In organophosphate poisoning, it can reactivate phosphorylated acetylcholinesterase before aging occurs.

It is particularly important for:

• Fasciculations
• Muscle weakness
• Respiratory muscle dysfunction

Its role is strongest in clinically significant organophosphate poisoning. The benefit in carbamate poisoning is less clearly established and depends on the specific exposure.

Seizures

Benzodiazepines are generally used for toxin-induced seizures.

Control of seizures is especially important because prolonged seizures increase:

• Oxygen demand
• Hyperthermia
• Rhabdomyolysis
• Secondary neurologic injury

Delayed Neurologic Syndromes

Organophosphate poisoning can occasionally produce neurologic complications after the initial cholinergic crisis.

Intermediate syndrome

• Develops after the acute cholinergic phase
• Characterized by proximal, neck, cranial, and respiratory muscle weakness

Organophosphate-induced delayed neuropathy

• Occurs later after selected organophosphate exposures
• May produce distal weakness and sensory abnormalities

Thus, apparent resolution of the initial secretory syndrome does not always mean neurologic risk has completely ended.

Key Points

• Cholinergic syndrome results from excess acetylcholine activity.
• Think “wet patient”: salivation, lacrimation, sweating, bronchorrhea, vomiting, diarrhea, and urination.
• Muscarinic effects → secretions, miosis, bronchospasm, bradycardia.
• Nicotinic effects → fasciculations, weakness/paralysis, tachycardia and hypertension.
• Respiratory failure results from a dangerous combination of bronchorrhea + bronchospasm + central depression + neuromuscular weakness.
• Diagnosis is primarily clinical; do not delay treatment while waiting for cholinesterase testing.
• Atropine treats muscarinic toxicity, particularly dangerous pulmonary secretions.
• Pralidoxime reactivates AChE before aging and is especially important in significant organophosphate poisoning.
• Atropine does not reverse nicotinic paralysis.
• Dermal decontamination is particularly important after pesticide exposure because continued skin absorption can prolong toxicity.

Toxicology – Bradypnea

Definition

Bradypnea is an abnormally slow respiratory rate for age. In toxicology, the clinically important issue is not the respiratory rate alone but whether the patient has inadequate ventilation, resulting in hypercapnia, hypoxemia, or inability to protect the airway.

A patient can have a relatively normal respiratory rate but still hypoventilate because the tidal volume is too small.

Pathophysiology

Toxin-associated respiratory depression can result from:

• Depression of the brainstem respiratory center
• Reduced responsiveness to carbon dioxide
• CNS depression with loss of airway protection
• Neuromuscular weakness or paralysis
• Respiratory muscle fatigue

Progressive hypoventilation causes:

CO₂ retention → respiratory acidosis → hypoxemia → cardiovascular/CNS injury → respiratory arrest

Major Toxicologic Causes

Opioids

The classic opioid toxidrome includes:

• Respiratory depression
• CNS depression
• Miosis

Other findings may include:

• Reduced bowel sounds
• Bradycardia
• Hypotension

Key Point: Respiratory depression is the most clinically important feature. Miosis supports the diagnosis but is not always present.

Sedative-Hypnotics

Examples include:

• Benzodiazepines
• Barbiturates
• Ethanol
• Other sedative-hypnotic agents

Typical findings:

• CNS depression
• Slurred speech
• Ataxia
• Reduced respiratory drive in severe poisoning

Isolated benzodiazepine poisoning often causes substantial sedation with relatively preserved respiration; severe respiratory depression should raise concern for coingestants, especially opioids or ethanol.

Clonidine and Imidazolines

These can produce an opioid-like syndrome with:

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

Cholinergic Poisoning

Organophosphate and carbamate poisoning can compromise respiration through several simultaneous mechanisms:

• Bronchorrhea
• Bronchospasm
• Central respiratory depression
• Neuromuscular weakness

Associated findings include:

• Miosis
• Salivation
• Lacrimation
• Sweating
• Vomiting and diarrhea
• Fasciculations
• Progressive weakness

Neuromuscular Paralysis

Respiratory failure can also result from paralysis rather than reduced central respiratory drive.

Important examples include:

• Botulism
• Severe organophosphate poisoning
• Tetrodotoxin
• Other neuroparalytic exposures

The patient may remain mentally alert while becoming progressively unable to ventilate.

Nontoxicologic Causes

Important alternatives include:

• Intracranial hemorrhage or other CNS lesions
• Severe hypoglycemia
• Electrolyte or metabolic abnormalities
• Hypothermia
• Neuromuscular disease
• Guillain–Barré syndrome
• Severe pulmonary disease with respiratory muscle exhaustion

A patient who was initially tachypneic and subsequently becomes bradypneic may be developing respiratory fatigue and impending arrest.

Clinical Features

Patients may not recognize their respiratory impairment because altered mental status frequently accompanies toxicologic bradypnea.

Possible findings include:

• Slow or shallow respirations
• Somnolence
• Reduced responsiveness
• Cyanosis
• Hypotension
• Bradycardia in advanced hypoxia
• Inability to protect the airway

Severe hypoventilation can progress rapidly to respiratory arrest.

Pupillary Clues

Miosis

• Opioids
• Clonidine/imidazolines
• Cholinergic poisoning

Dilated pupils

• Severe hypoxia
• Sympathomimetic coexposure
• Antimuscarinic coexposure

Pupil size should therefore be treated as a diagnostic clue rather than a definitive test.

Oxygenation vs. Ventilation

This distinction is especially important.

Pulse oximetry measures oxygenation.

It does not directly measure ventilation or carbon dioxide clearance.

A hypoventilating patient receiving supplemental oxygen can therefore maintain a reassuring oxygen saturation while accumulating dangerous amounts of CO₂.

Assessment may require:

• Respiratory rate and depth
• Mental status
• Pulse oximetry
• Capnography (end-tidal CO₂) when available
• Blood gas analysis in significant or persistent hypoventilation

Evaluation

Initial assessment should focus on:

• Airway patency
• Respiratory rate and depth
• Oxygenation
• Ventilation
• Mental status
• Blood glucose
• Hemodynamic status

Additional investigations may include:

• ECG
• Electrolytes and renal function
• Blood gas
• Chest radiograph when aspiration or pulmonary disease is suspected
• Targeted toxicant concentrations
• Brain imaging when an intracranial cause is possible

Routine urine toxicology screening has important limitations and should not delay treatment.

Management

Airway and ventilation are the immediate priorities.

Management may include:

• Airway positioning and suction
• Supplemental oxygen when hypoxemic
• Assisted ventilation with bag-mask ventilation when needed
• Continuous respiratory monitoring
• Endotracheal intubation and mechanical ventilation when adequate ventilation or airway protection cannot be maintained

Treatment should not be delayed while waiting to identify the exact poison.

Naloxone

Naloxone should be used when opioid-induced respiratory depression is suspected.

The therapeutic goal is restoration of:

• Adequate respiratory rate
• Adequate tidal volume
• Airway protection

Complete awakening is not necessarily required.

Because naloxone may wear off before the opioid does, patients can develop recurrent respiratory depression and require continued monitoring and sometimes repeated therapy.

Naloxone can precipitate acute withdrawal in opioid-dependent patients.

Glucose

Blood glucose should be checked promptly in patients with altered consciousness.

Hypoglycemia should be corrected when present rather than giving dextrose automatically to every patient with depressed mental status.

Decontamination

Do not induce vomiting in a patient with respiratory or CNS depression because aspiration risk is high.

Older references recommended routine gastric lavage in critically poisoned patients. This is not standard modern practice and can substantially increase aspiration and procedural risk.

Activated charcoal should generally be avoided when airway protective reflexes are impaired unless the airway has been appropriately protected and charcoal is otherwise indicated.

Aspiration

Depressed consciousness and loss of airway reflexes increase the risk of aspiration.

Consider aspiration when there is:

• Vomiting
• Hypoxemia
• Coughing
• Abnormal lung examination
• New pulmonary infiltrates

Aspiration can produce chemical pneumonitis and secondary respiratory complications.

Key Points

• Bradypnea is dangerous when it represents inadequate ventilation.
• Respiratory rate alone can underestimate respiratory failure; assess tidal volume and overall ventilation.
• Opioids are a major toxicologic cause of respiratory depression.
• Opioid toxicity classically causes CNS depression + respiratory depression + miosis.
• Clonidine/imidazolines can closely mimic opioid poisoning.
• Cholinergic poisoning can cause respiratory failure through secretions, bronchospasm, central depression, and muscle weakness.
• Pulse oximetry assesses oxygenation but does not exclude hypercapnic hypoventilation.
• Capnography can help detect inadequate ventilation earlier.
• Naloxone is indicated when opioid-related respiratory depression is suspected; the goal is adequate ventilation, not necessarily full consciousness.
• Significant hypoventilation requires immediate airway and ventilatory support.
• A transition from tachypnea to bradypnea in a deteriorating patient may indicate respiratory exhaustion and impending arrest.

Toxicology – Bradycardia Toxidrome

Definition

Bradycardia is a heart rate that is slower than expected for the patient’s age and physiologic condition.

In adults, it is conventionally defined as a resting heart rate <60 beats/min, although the clinical importance depends more on whether the slow rate is causing poor perfusion or hemodynamic instability.

A patient with an asymptomatic slow heart rate and adequate perfusion does not necessarily require treatment.

Pathophysiology

Toxicologic bradycardia can result from several mechanisms:

• β-adrenergic receptor blockade
• Calcium-channel blockade
• Cardiac sodium-channel blockade
• Increased cholinergic activity
• Increased vagal tone
• Suppression of sympathetic outflow
• Direct myocardial depression
• Abnormal cardiac conduction

Nontoxicologic mechanisms include:

• Hypoxia
• Hypothermia
• Hyperkalemia
• Hypermagnesemia
• Myocardial ischemia/infarction
• Increased intracranial pressure

Important Toxicologic Causes

Beta-blockers

• Bradycardia
• Hypotension
• AV block
• Myocardial depression
• CNS depression or seizures with some agents

Severe poisoning can produce cardiogenic shock.

Calcium-channel blockers

• Bradycardia
• Hypotension
• AV block
• Myocardial depression

A useful metabolic clue is hyperglycemia, particularly in severe calcium-channel blocker poisoning.

Digoxin and other cardiac glycosides

• Bradycardia or AV block
• Nausea and vomiting
• Visual disturbances
• Hyperkalemia in significant acute poisoning
• Numerous atrial and ventricular dysrhythmias

Clonidine and imidazolines

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

This presentation may resemble opioid poisoning.

Opioids

• CNS depression
• Respiratory depression
• Miosis
• Bradycardia in significant poisoning

Cholinergic agents

Examples include organophosphate and carbamate insecticides.

Typical associated findings include:

• Salivation
• Lacrimation
• Bronchorrhea
• Vomiting and diarrhea
• Urination
• Miosis
• Sweating

Nicotinic manifestations such as fasciculations and muscle weakness particularly support organophosphate/carbamate toxicity.

Other Possible Toxicologic Causes

Bradycardia can also occur with selected exposures involving:

• Baclofen
• Lithium
• Antiarrhythmic drugs
• Certain mushrooms
• Tetrodotoxin
• Saxitoxin
• Other cardiotoxic or neurotoxic agents

The accompanying toxidrome is usually more useful than bradycardia alone for identifying the cause.

Clinical Features

The major question is whether bradycardia is causing inadequate cardiac output.

Concerning findings include:

• Hypotension
• Altered mental status
• Syncope
• Chest discomfort
• Signs of shock
• Pulmonary edema
• Poor peripheral perfusion

Severe poisoning may progress to:

• High-grade AV block
• Ventricular dysrhythmias
• Cardiogenic shock
• Cardiac arrest

Diagnostic Clues

Miosis + respiratory/CNS depression

→ opioid, clonidine, or imidazoline exposure

Bradycardia + hyperglycemia

→ consider calcium-channel blocker toxicity

Bradycardia + hypoglycemia/CNS toxicity

→ may suggest severe beta-blocker poisoning

Bradycardia + vomiting + visual disturbance + hyperkalemia

→ consider digoxin toxicity

Bradycardia + miosis + bronchorrhea + secretions

→ consider cholinergic poisoning

Evaluation

Important investigations include:

• 12-lead ECG
• Continuous cardiac monitoring
• Blood pressure and perfusion assessment
• Pulse oximetry
• Blood glucose
• Electrolytes
• Renal function

Depending on the suspected exposure, additional testing may include:

• Potassium, magnesium and calcium
• Digoxin concentration
• Cholinesterase testing
• Targeted toxicant concentrations
• Acetaminophen concentration when an intentional or unknown overdose is possible

Routine broad urine drug screening is usually less useful than targeted testing based on the clinical toxidrome.

ECG Findings

The ECG helps identify both the severity and possible mechanism.

Possible abnormalities include:

• Sinus bradycardia
• PR prolongation
• AV block
• QRS widening
• QT abnormalities
• Ventricular dysrhythmias

QRS widening should raise concern for an additional sodium-channel-blocking effect rather than simple sinus-node suppression alone.

Management

Treatment is determined by perfusion and underlying cause, not simply by the heart-rate number.

Initial priorities include:

• Airway and ventilation when required
• IV access
• Continuous cardiac monitoring
• Correction of hypoxia
• Correction of important electrolyte or glucose abnormalities
• Appropriate IV fluids when hypovolemia is present

Excessive fluid administration should be avoided when significant myocardial depression is suspected.

Atropine

Atropine may be attempted for symptomatic bradycardia, particularly when increased vagal activity or AV-nodal dysfunction contributes.

However, atropine may be ineffective in severe toxicologic bradycardia, especially with major beta-blocker or calcium-channel blocker poisoning.

Failure of atropine should prompt treatment directed at the responsible toxicant rather than repeated reliance on atropine alone.

Cause-Specific Therapy

Beta-blocker poisoning

• Supportive cardiovascular care
• Vasopressors when necessary
• High-dose insulin euglycemia therapy for severe cardiotoxicity
• Glucagon may be considered, although contemporary practice generally regards it as an adjunct rather than the central therapy.

Calcium-channel blocker poisoning

• IV calcium
• High-dose insulin euglycemia therapy
• Vasopressor support
• Additional rescue therapies in refractory cases

Digoxin toxicity

• Digoxin immune Fab for severe poisoning

Opioid toxicity

• Naloxone when clinically significant respiratory depression is present
• Ventilatory support when necessary

Organophosphate/carbamate toxicity

• Atropine for clinically important muscarinic manifestations
• Pralidoxime is particularly relevant to significant organophosphate poisoning.

Refractory Bradycardia and Shock

When severe bradycardia remains associated with inadequate perfusion despite initial treatment, management may require:

• Vasopressors
• Toxicant-specific antidotal therapy
• Temporary cardiac pacing in selected cases
• Advanced mechanical circulatory support for refractory cardiogenic shock

Importantly, electrical pacing may restore the heart rate without adequately correcting drug-induced myocardial contractile failure, so the underlying poisoning must still be treated.

Decontamination

Older sources recommended routine gastric lavage for poisoned patients with bradycardia. This is not standard modern management.

Activated charcoal may be considered after selected recent ingestions when:

• The substance is adsorbed by charcoal.
• The expected benefit is meaningful.
• The airway is intact or protected.

Decontamination should never delay stabilization of an unstable patient.

Key Points

• Treat symptomatic bradycardia and poor perfusion, not the heart-rate number alone.
• Major toxicologic causes include beta-blockers, calcium-channel blockers, digoxin, clonidine/imidazolines, opioids, and cholinergic agents.
• Bradycardia + hyperglycemia → think calcium-channel blocker toxicity.
• Bradycardia + hypoglycemia/CNS effects → consider beta-blocker toxicity.
• Bradycardia + GI/visual symptoms + hyperkalemia → think digoxin.
• Bradycardia + miosis + respiratory depression → think opioids or clonidine/imidazolines.
• Bradycardia + bronchorrhea/secretions → think cholinergic poisoning.
• Atropine can be attempted in symptomatic bradycardia but may be ineffective in severe cardiotoxic poisoning.
• Severe beta-blocker and calcium-channel blocker poisoning often requires high-dose insulin therapy plus hemodynamic support.
• ECG and continuous cardiac monitoring are essential in clinically significant toxicologic bradycardia.