Toxicology – Body Packers and Body Stuffers

Definitions

A body packer deliberately conceals multiple drug packets within the gastrointestinal tract or another body cavity for transportation or concealment. The packets are usually carefully wrapped and may contain a large total quantity of drug.

A body stuffer hastily swallows or conceals drugs, typically to avoid discovery. Packaging is generally less secure, making leakage more likely, although the total quantity concealed is usually smaller.

This distinction matters clinically:

• Body packer → larger drug burden, better packaging, but packet rupture can cause catastrophic poisoning.
• Body stuffer → smaller burden but poorer packaging and greater likelihood of early leakage.

Pathophysiology

Complications arise through two major mechanisms:

Drug toxicity

• Leakage or rupture releases the packet contents.
• Clinical findings depend on the concealed drug.
• A ruptured body-packer packet can release a very large amount and cause rapidly life-threatening toxicity.

Mechanical complications

• Bowel obstruction
• GI perforation
• Local tissue injury
• Rarely ischemia or other surgical complications

Abrupt deterioration in a known or suspected body packer should raise immediate concern for packet rupture.

Commonly Concealed Drugs

Historically common substances include:

• Cocaine
• Heroin and other opioids
• Amphetamines
• MDMA
• Cannabis products

The clinical toxidrome depends on the actual substance and possible adulterants.

Clinical Features

An asymptomatic patient may remain well while packets are intact.

Symptoms can arise from either drug leakage or GI complications.

Stimulant leakage may cause:

• Agitation
• Tachycardia
• Hypertension
• Hyperthermia
• Mydriasis
• Seizures
• Dysrhythmias
• Severe cardiovascular or neurologic complications

Opioid leakage may cause:

• CNS depression
• Miosis
• Bradypnea
• Hypoventilation
• Respiratory arrest

Mechanical complications may cause:

• Abdominal pain
• Vomiting
• Abdominal distension
• Tenderness
• Reduced bowel sounds
• Features of obstruction or perforation

Severe Complications

Major complications include:

• Respiratory failure
• Seizures
• Hyperthermia
• Rhabdomyolysis
• Acute kidney injury
• Dysrhythmias
• Myocardial ischemia
• Bowel obstruction
• GI perforation
• Shock

A symptomatic body packer requires urgent evaluation and surgical consultation because packet rupture can produce overwhelming drug exposure.

Diagnosis

Diagnosis combines:

• History and circumstances
• Clinical examination
• Identification of the toxidrome
• Appropriate imaging

Routine urine drug screening is not reliable for determining whether packets are present and cannot establish packet number or integrity.

Imaging

Body Packers

Modern evaluation generally favors CT of the abdomen/pelvis without oral or rectal contrast when accurate packet detection is required.

CT is substantially more sensitive than plain abdominal radiography for detecting concealed packets and associated complications.

Plain abdominal radiographs may show packets but can miss them, particularly with modern packaging techniques.

Body Stuffers

Routine imaging is less useful because:

• Packets are smaller.
• Fewer packets are usually present.
• Improvised packaging may be difficult to visualize.

Imaging is particularly important when obstruction, perforation, or another surgical complication is suspected.

Management

Initial management follows standard toxicologic priorities:

• Airway and ventilation
• Circulatory support
• Cardiac monitoring when indicated
• Temperature management
• Treatment of seizures and agitation
• Recognition of the specific toxidrome

Clinical deterioration should be treated immediately rather than waiting for confirmation of packet rupture.

Gastrointestinal Management

Do not induce vomiting.

Manipulation that could rupture a packet should generally be avoided.

For an asymptomatic body packer with intact packets, whole-bowel irrigation with polyethylene glycol electrolyte solution may be considered under specialist supervision to facilitate packet passage.

Activated charcoal may have a role in selected cases, particularly when packet leakage is suspected and the substance is charcoal-adsorbable, but it is not a substitute for definitive management of packet rupture or obstruction.

Routine endoscopic retrieval of GI packets is generally avoided because manipulation can rupture them. Management should be individualized with toxicology, gastroenterology, and surgical input when packets fail to progress or are in anatomically unusual locations.

Packet Rupture or GI Complications

Urgent surgical involvement is required when there is:

• Suspected packet rupture with severe toxicity
• Bowel obstruction
• GI perforation
• Significant bleeding or ischemia
• Failure of packets to progress when clinically concerning

A ruptured packet containing a highly potent drug can cause rapidly fatal poisoning, so supportive resuscitation and definitive management occur simultaneously.

Opioid Toxicity

When opioid leakage produces respiratory depression:

• Naloxone is the specific antagonist.
• Repeated administration or continuous infusion may be necessary when opioid exposure persists.
• Ventilatory support is essential when adequate ventilation cannot otherwise be maintained.

The goal of naloxone is restoration of adequate breathing, rather than necessarily complete arousal.

Stimulant Toxicity

Cocaine or amphetamine leakage may produce severe sympathomimetic toxicity.

Management centers on:

• Benzodiazepines for agitation and seizures
• Aggressive external cooling for severe hyperthermia
• Cardiovascular supportive care
• Management of complications such as rhabdomyolysis

Observation

Body packers generally require monitored medical management until packet passage has been adequately confirmed and the patient remains clinically stable.

Body stuffers usually have fewer packets but may develop toxicity sooner because of poor packaging. Observation requirements depend on the substance, packaging, symptoms, and circumstances.

Key Points

• Body packer = carefully packaged, large total drug quantity, catastrophic consequences if a packet ruptures.
• Body stuffer = hurried concealment, poorer packaging, usually smaller drug quantity and earlier leakage risk.
• Sudden deterioration in a body packer should strongly suggest packet rupture.
• Abdominal pain or vomiting raises concern for obstruction or perforation.
• CT is generally more sensitive than plain radiography for detecting body-packer packets.
• Routine urine drug screening cannot reliably exclude concealed packets.
• Do not induce vomiting or routinely manipulate packets endoscopically.
• Whole-bowel irrigation may be used for selected asymptomatic body packers with intact packets.
• Opioid leakage → respiratory support + naloxone.
• Stimulant leakage → supportive care, benzodiazepines, cooling, and treatment of cardiovascular complications.
• Severe toxicity or a surgical abdominal complication requires urgent multidisciplinary management.

Toxicology – The Initially Asymptomatic Patient

Definition

A patient may initially appear completely well after a potentially serious toxic exposure. Some poisons have latent periods before major clinical effects develop, while others have delayed absorption, delayed formation of toxic metabolites, or delayed organ injury.

Therefore:

Asymptomatic now ≠ nontoxic exposure.

Why Toxicity May Be Delayed

Delayed toxicity can occur because of:

• Slow or prolonged absorption
• Sustained/extended-release formulations
• Formation of toxic metabolites
• Delayed cellular or organ injury
• Enterohepatic recirculation
• Coingestion that delays metabolism
• Initially intact drug packets that later rupture
• Toxic effects that require depletion of physiologic reserves

The expected observation period therefore depends on the specific toxicant, formulation, dose, time of exposure, and patient factors.

Important Exposures with Delayed Toxicity

Acetaminophen

Patients may initially have few or nonspecific symptoms despite a potentially hepatotoxic exposure.

Later findings can include:

• Nausea and vomiting
• Right-upper-quadrant discomfort
• Increasing aminotransferases
• Hepatic failure in severe cases
• Occasionally renal or pancreatic injury

Key Point: Do not use absence of early symptoms to exclude significant acetaminophen toxicity. Risk assessment depends heavily on the timed serum acetaminophen concentration and exposure history.

Anticoagulants / Long-Acting Anticoagulant Rodenticides

Coagulation abnormalities and bleeding may be delayed.

Possible manifestations include:

• Epistaxis
• Gingival bleeding
• Hematuria
• GI bleeding
• Easy bruising

Long-acting anticoagulant rodenticides can produce particularly prolonged coagulopathy.

Arsenic and Thallium

Acute large exposures often cause early GI symptoms, but repeated or smaller exposures may produce delayed systemic manifestations.

Arsenic

• Painful peripheral neuropathy
• Skin changes
• Weakness

Thallium

• Painful neuropathy
• Alopecia
• Neurologic abnormalities

Delayed toxicity may evolve over days to weeks.

Body Packers

Patients carrying internally concealed drug packets may initially be asymptomatic while the packages remain intact.

Packet leakage or rupture can cause sudden, severe poisoning determined by the substance contained within the packet.

This is a high-risk situation because each packet may contain a substantial quantity of drug.

Button Batteries

An esophageal button battery can produce severe tissue injury before obvious symptoms develop.

Modern understanding emphasizes that injury is caused mainly by generation of an electrical current and local hydroxide production, rather than simply leakage of caustic battery contents.

Key Point: Suspected esophageal button-battery impaction is an emergency and should not be managed according to the patient’s apparent lack of symptoms.

Diphenoxylate/Atropine

Toxicity can be delayed, particularly after significant pediatric exposure.

Possible later findings include:

• CNS depression
• Respiratory depression
• Opioid manifestations
• Antimuscarinic findings from atropine

Ethylene Glycol

Early intoxication can resemble ethanol exposure or appear relatively mild.

As toxic metabolites accumulate, patients may develop:

• High-anion-gap metabolic acidosis
• Tachypnea
• Cardiovascular instability
• Hypocalcemia
• Acute kidney injury

Coingested ethanol can delay toxicity because it competes for alcohol dehydrogenase.

Hydrofluoric Acid

Dilute dermal exposures may initially look minor while deeper tissue injury develops.

Later manifestations can include:

• Severe pain
• Progressive tissue injury
• Hypocalcemia
• Hypomagnesemia
• Ventricular dysrhythmias after significant systemic exposure

The severity of pain can be disproportionate to the initial skin appearance.

Lead

Significant exposure may initially be subtle.

Subsequent manifestations can include:

• Abdominal symptoms
• Anemia
• Neurologic abnormalities
• Encephalopathy in severe poisoning

Methanol

Patients may have an initial latent period before toxic metabolites accumulate.

Later manifestations include:

• High-anion-gap metabolic acidosis
• Headache
• Altered mental status
• Visual disturbances
• Severe visual injury
• Coma in severe cases

Ethanol coingestion can delay toxicity by competing for alcohol dehydrogenase.

Methylene Chloride

Methylene chloride is metabolized partly to carbon monoxide.

Consequently, carboxyhemoglobin concentrations and CO-related toxicity may persist or become apparent after the original exposure has ended.

Mercury

Certain organic mercury compounds can have a long latent period before neurologic toxicity becomes clinically apparent.

Potential manifestations include:

• Sensory disturbances
• Ataxia
• Visual or auditory abnormalities
• Other neurologic dysfunction

Monoamine Oxidase Inhibitors (MAOIs)

Significant overdose may initially appear deceptively mild.

Delayed toxicity can include:

• Agitation
• Hyperthermia
• Hypertension or hypotension
• Tachycardia
• Rigidity
• Seizures
• Coma

Significant MAOI overdose therefore requires prolonged clinical observation.

Hepatotoxic Mushrooms

Certain amatoxin-containing mushrooms, particularly Amanita species, can produce a characteristic delayed syndrome.

Typical course:

1. Initial latent period
2. Severe vomiting and diarrhea
3. Apparent temporary improvement
4. Progressive hepatic injury or liver failure

Key Point: GI symptoms beginning more than about 6 hours after mushroom ingestion raise concern for potentially serious mushroom poisoning, although timing alone does not establish the species or toxin.

Naphthalene

Hemolysis may be delayed after exposure.

Possible findings include:

• Weakness
• Abdominal symptoms
• Jaundice
• Dark urine
• Anemia

Patients with G6PD deficiency are particularly susceptible to oxidant-induced hemolysis.

Sulfonylureas and Other Insulin Secretagogues

Hypoglycemia may be delayed and can recur.

Manifestations include:

• Sweating
• Tremor
• Confusion
• Behavioral changes
• Seizures
• Coma

Long-acting preparations and pediatric exposures can require prolonged glucose monitoring.

Quinine

Toxicity can include delayed:

• Visual impairment
• Tinnitus
• CNS effects
• Hypotension
• Cardiac conduction abnormalities and dysrhythmias

Snake Envenomation

Some envenomations may initially produce few findings.

Depending on the species, delayed effects can include:

• Progressive swelling and pain
• Ecchymosis
• Coagulopathy
• Neurotoxicity
• Weakness or paralysis

Absence of immediate symptoms does not reliably exclude clinically important envenomation.

Sustained-Release / Extended-Release Drugs

Modified-release preparations can produce delayed and prolonged absorption.

Potentially important examples include extended-release formulations of:

• Calcium-channel blockers
• Beta-blockers
• Lithium
• Theophylline
• Salicylates

The manifestations depend on the specific drug.

Key Point: Standard observation periods appropriate for immediate-release drugs may be inadequate after extended-release ingestion.

Assessment

For an asymptomatic patient with a potentially serious exposure, determine:

• Exact substance
• Formulation: immediate vs. extended release
• Estimated amount
• Time of exposure
• Route
• Coingestants
• Relevant medical conditions
• Whether delayed toxicity is characteristic of the substance

Investigations should be toxin-specific, rather than relying on a routine broad drug screen.

Examples may include:

• ECG
• Glucose
• Electrolytes and renal function
• Acid-base assessment
• Acetaminophen concentration
• Salicylate concentration
• Coagulation studies
• Other targeted toxicant concentrations

Observation and Disposition

A patient should not be considered safe for discharge solely because the initial examination is normal.

The appropriate observation period depends on:

• Toxicant
• Dose
• Formulation
• Expected toxicokinetics
• Laboratory findings
• Development of symptoms

Some exposures require serial laboratory measurements or prolonged monitoring despite an initially normal examination.

Key Points

• Absence of symptoms does not exclude serious poisoning.
• Acetaminophen can cause major hepatic injury despite minimal early symptoms.
• Methanol and ethylene glycol become more dangerous as toxic metabolites accumulate.
• Extended-release formulations can substantially delay toxicity.
• Amatoxin mushroom poisoning may have a deceptive latent period followed by GI illness and later hepatic failure.
• Button batteries can cause severe esophageal injury before symptoms become obvious.
• Sulfonylurea-induced hypoglycemia can be delayed and recurrent.
• Body-packet rupture can convert an asymptomatic presentation into catastrophic toxicity.
• Observation and testing should be based on the specific exposure, not simply on how well the patient initially appears.

Toxicology – The Initially Asymptomatic Patient

Definition

A patient may initially appear completely well after a potentially serious toxic exposure. Some poisons have latent periods before major clinical effects develop, while others have delayed absorption, delayed formation of toxic metabolites, or delayed organ injury.

Therefore:

Asymptomatic now ≠ nontoxic exposure.

Why Toxicity May Be Delayed

Delayed toxicity can occur because of:

• Slow or prolonged absorption
• Sustained/extended-release formulations
• Formation of toxic metabolites
• Delayed cellular or organ injury
• Enterohepatic recirculation
• Coingestion that delays metabolism
• Initially intact drug packets that later rupture
• Toxic effects that require depletion of physiologic reserves

The expected observation period therefore depends on the specific toxicant, formulation, dose, time of exposure, and patient factors.

Important Exposures with Delayed Toxicity

Acetaminophen

Patients may initially have few or nonspecific symptoms despite a potentially hepatotoxic exposure.

Later findings can include:

• Nausea and vomiting
• Right-upper-quadrant discomfort
• Increasing aminotransferases
• Hepatic failure in severe cases
• Occasionally renal or pancreatic injury

Key Point: Do not use absence of early symptoms to exclude significant acetaminophen toxicity. Risk assessment depends heavily on the timed serum acetaminophen concentration and exposure history.

Anticoagulants / Long-Acting Anticoagulant Rodenticides

Coagulation abnormalities and bleeding may be delayed.

Possible manifestations include:

• Epistaxis
• Gingival bleeding
• Hematuria
• GI bleeding
• Easy bruising

Long-acting anticoagulant rodenticides can produce particularly prolonged coagulopathy.

Arsenic and Thallium

Acute large exposures often cause early GI symptoms, but repeated or smaller exposures may produce delayed systemic manifestations.

Arsenic

• Painful peripheral neuropathy
• Skin changes
• Weakness

Thallium

• Painful neuropathy
• Alopecia
• Neurologic abnormalities

Delayed toxicity may evolve over days to weeks.

Body Packers

Patients carrying internally concealed drug packets may initially be asymptomatic while the packages remain intact.

Packet leakage or rupture can cause sudden, severe poisoning determined by the substance contained within the packet.

This is a high-risk situation because each packet may contain a substantial quantity of drug.

Button Batteries

An esophageal button battery can produce severe tissue injury before obvious symptoms develop.

Modern understanding emphasizes that injury is caused mainly by generation of an electrical current and local hydroxide production, rather than simply leakage of caustic battery contents.

Key Point: Suspected esophageal button-battery impaction is an emergency and should not be managed according to the patient’s apparent lack of symptoms.

Diphenoxylate/Atropine

Toxicity can be delayed, particularly after significant pediatric exposure.

Possible later findings include:

• CNS depression
• Respiratory depression
• Opioid manifestations
• Antimuscarinic findings from atropine

Ethylene Glycol

Early intoxication can resemble ethanol exposure or appear relatively mild.

As toxic metabolites accumulate, patients may develop:

• High-anion-gap metabolic acidosis
• Tachypnea
• Cardiovascular instability
• Hypocalcemia
• Acute kidney injury

Coingested ethanol can delay toxicity because it competes for alcohol dehydrogenase.

Hydrofluoric Acid

Dilute dermal exposures may initially look minor while deeper tissue injury develops.

Later manifestations can include:

• Severe pain
• Progressive tissue injury
• Hypocalcemia
• Hypomagnesemia
• Ventricular dysrhythmias after significant systemic exposure

The severity of pain can be disproportionate to the initial skin appearance.

Lead

Significant exposure may initially be subtle.

Subsequent manifestations can include:

• Abdominal symptoms
• Anemia
• Neurologic abnormalities
• Encephalopathy in severe poisoning

Methanol

Patients may have an initial latent period before toxic metabolites accumulate.

Later manifestations include:

• High-anion-gap metabolic acidosis
• Headache
• Altered mental status
• Visual disturbances
• Severe visual injury
• Coma in severe cases

Ethanol coingestion can delay toxicity by competing for alcohol dehydrogenase.

Methylene Chloride

Methylene chloride is metabolized partly to carbon monoxide.

Consequently, carboxyhemoglobin concentrations and CO-related toxicity may persist or become apparent after the original exposure has ended.

Mercury

Certain organic mercury compounds can have a long latent period before neurologic toxicity becomes clinically apparent.

Potential manifestations include:

• Sensory disturbances
• Ataxia
• Visual or auditory abnormalities
• Other neurologic dysfunction

Monoamine Oxidase Inhibitors (MAOIs)

Significant overdose may initially appear deceptively mild.

Delayed toxicity can include:

• Agitation
• Hyperthermia
• Hypertension or hypotension
• Tachycardia
• Rigidity
• Seizures
• Coma

Significant MAOI overdose therefore requires prolonged clinical observation.

Hepatotoxic Mushrooms

Certain amatoxin-containing mushrooms, particularly Amanita species, can produce a characteristic delayed syndrome.

Typical course:

1. Initial latent period
2. Severe vomiting and diarrhea
3. Apparent temporary improvement
4. Progressive hepatic injury or liver failure

Key Point: GI symptoms beginning more than about 6 hours after mushroom ingestion raise concern for potentially serious mushroom poisoning, although timing alone does not establish the species or toxin.

Naphthalene

Hemolysis may be delayed after exposure.

Possible findings include:

• Weakness
• Abdominal symptoms
• Jaundice
• Dark urine
• Anemia

Patients with G6PD deficiency are particularly susceptible to oxidant-induced hemolysis.

Sulfonylureas and Other Insulin Secretagogues

Hypoglycemia may be delayed and can recur.

Manifestations include:

• Sweating
• Tremor
• Confusion
• Behavioral changes
• Seizures
• Coma

Long-acting preparations and pediatric exposures can require prolonged glucose monitoring.

Quinine

Toxicity can include delayed:

• Visual impairment
• Tinnitus
• CNS effects
• Hypotension
• Cardiac conduction abnormalities and dysrhythmias

Snake Envenomation

Some envenomations may initially produce few findings.

Depending on the species, delayed effects can include:

• Progressive swelling and pain
• Ecchymosis
• Coagulopathy
• Neurotoxicity
• Weakness or paralysis

Absence of immediate symptoms does not reliably exclude clinically important envenomation.

Sustained-Release / Extended-Release Drugs

Modified-release preparations can produce delayed and prolonged absorption.

Potentially important examples include extended-release formulations of:

• Calcium-channel blockers
• Beta-blockers
• Lithium
• Theophylline
• Salicylates

The manifestations depend on the specific drug.

Key Point: Standard observation periods appropriate for immediate-release drugs may be inadequate after extended-release ingestion.

Assessment

For an asymptomatic patient with a potentially serious exposure, determine:

• Exact substance
• Formulation: immediate vs. extended release
• Estimated amount
• Time of exposure
• Route
• Coingestants
• Relevant medical conditions
• Whether delayed toxicity is characteristic of the substance

Investigations should be toxin-specific, rather than relying on a routine broad drug screen.

Examples may include:

• ECG
• Glucose
• Electrolytes and renal function
• Acid-base assessment
• Acetaminophen concentration
• Salicylate concentration
• Coagulation studies
• Other targeted toxicant concentrations

Observation and Disposition

A patient should not be considered safe for discharge solely because the initial examination is normal.

The appropriate observation period depends on:

• Toxicant
• Dose
• Formulation
• Expected toxicokinetics
• Laboratory findings
• Development of symptoms

Some exposures require serial laboratory measurements or prolonged monitoring despite an initially normal examination.

Key Points

• Absence of symptoms does not exclude serious poisoning.
• Acetaminophen can cause major hepatic injury despite minimal early symptoms.
• Methanol and ethylene glycol become more dangerous as toxic metabolites accumulate.
• Extended-release formulations can substantially delay toxicity.
• Amatoxin mushroom poisoning may have a deceptive latent period followed by GI illness and later hepatic failure.
• Button batteries can cause severe esophageal injury before symptoms become obvious.
• Sulfonylurea-induced hypoglycemia can be delayed and recurrent.
• Body-packet rupture can convert an asymptomatic presentation into catastrophic toxicity.
• Observation and testing should be based on the specific exposure, not simply on how well the patient initially appears.

Toxicology – Ascending Paralysis

Definition

Ascending paralysis is progressive flaccid weakness beginning in the lower extremities and moving upward toward the trunk and upper extremities. Severe cases can involve bulbar, facial, and respiratory muscles.

Because respiratory weakness can progress rapidly, ascending paralysis should be considered a potential neurologic emergency.

Major Causes

Important causes include:

Nontoxicologic

• Guillain–Barré syndrome (GBS) — the most important common cause
• Acute intermittent porphyria (AIP)
• Spinal cord disease or compression

Toxicologic

• Tick paralysis
• Tetrodotoxin
• Severe arsenic poisoning
• Karwinskia humboldtiana (coyotillo) poisoning
• Selected toxic neuropathies

Other disorders can cause weakness but follow different patterns. For example, botulism classically produces descending rather than ascending paralysis.

Guillain–Barré Syndrome

GBS is an acute immune-mediated peripheral neuropathy.

It commonly follows an infection, particularly:

• Campylobacter jejuni
• Cytomegalovirus
• Epstein–Barr virus
• Other respiratory or gastrointestinal infections

The classic presentation is:

• Symmetric progressive weakness
• Reduced or absent deep-tendon reflexes
• Weakness beginning in the legs
• Relatively mild sensory symptoms

Cranial nerves may also become involved, producing facial or bulbar weakness.

Autonomic dysfunction can cause:

• Tachycardia or bradycardia
• Hypertension or hypotension
• Dysrhythmias
• Urinary retention

Tick Paralysis

Certain ticks produce a neurotoxin capable of causing:

• Progressive symmetric weakness
• Reduced or absent reflexes
• Ascending flaccid paralysis
• Respiratory weakness in severe cases

Sensory function and mental status are generally preserved.

A careful skin and scalp examination for an attached tick is therefore important.

Removal of the causative tick usually leads to improvement, although respiratory support may temporarily be required.

Tetrodotoxin Poisoning

Tetrodotoxin is associated particularly with certain marine animals, including pufferfish.

Mechanism

Tetrodotoxin blocks voltage-gated sodium channels, preventing normal action-potential propagation.

Clinical features can include:

• Perioral and peripheral paresthesias
• Nausea and vomiting
• Weakness
• Dysphagia
• Cranial nerve abnormalities
• Progressive paralysis
• Respiratory failure

Neurologic effects can develop rapidly after significant exposure.

Arsenic

Severe arsenic poisoning can produce a painful sensorimotor peripheral neuropathy.

Early systemic toxicity may include:

• Severe nausea and vomiting
• Abdominal pain
• Profuse diarrhea
• Cardiovascular instability

Neurologic manifestations can later include:

• Painful paresthesias
• Sensory loss
• Reduced reflexes
• Progressive weakness
• Occasionally ascending paralysis

Acute Intermittent Porphyria

AIP can produce a motor neuropathy that occasionally progresses to severe paralysis.

An acute attack may include:

• Severe abdominal pain
• Nausea and vomiting
• Tachycardia
• Hypertension
• Psychiatric or behavioral manifestations
• Peripheral neuropathy
• Motor weakness
• Hyponatremia

Urinary porphobilinogen (PBG) is an important diagnostic test during a suspected acute attack.

Clinical Features

The characteristic neurologic pattern is:

• Symmetric lower-extremity weakness
• Progression toward the trunk and arms
• Reduced or absent reflexes
• Possible mild paresthesias
• Eventual bulbar or facial involvement
• Respiratory muscle weakness in severe disease

The associated symptoms help identify the underlying cause.

Respiratory Assessment

The most immediately dangerous complication is neuromuscular respiratory failure.

Patients require repeated assessment of:

• Respiratory rate and effort
• Oxygenation
• Ability to handle secretions
• Cough strength
• Bulbar function
• Objective respiratory muscle strength, such as serial forced vital capacity and inspiratory pressure measurements

A normal pulse oximetry reading does not reliably exclude impending ventilatory failure, because oxygenation may remain normal until respiratory weakness becomes advanced.

Airway management should therefore be based on the overall clinical trajectory rather than waiting for a single rigid vital-capacity threshold.

Diagnostic Evaluation

Testing is directed toward the suspected cause.

Possible investigations include:

• Electrolytes
• Calcium and magnesium
• Renal function
• ECG and cardiac monitoring
• Blood gas when respiratory failure is suspected
• Serial respiratory function measurements

Additional targeted tests may include:

• Blood lead concentration
• Arsenic testing
• Urinary porphobilinogen for suspected AIP
• Cholinesterase testing when organophosphate poisoning is suspected
• Nerve-conduction studies/electromyography
• Neuroimaging when spinal cord or CNS pathology is possible

GBS Diagnosis

Lumbar puncture classically demonstrates:

Elevated CSF protein with relatively few white blood cells

This is called albuminocytologic dissociation.

However, CSF protein may still be normal early in the illness, so a normal early lumbar puncture does not exclude GBS.

Differential Diagnosis

Important alternatives include:

• GBS
• Tick paralysis
• Tetrodotoxin poisoning
• Acute porphyria
• Severe toxic neuropathy
• Electrolyte abnormalities
• Myasthenia gravis
• Spinal cord disease
• Botulism

Botulism distinction: botulism typically begins with cranial nerve dysfunction and produces symmetric descending paralysis.

Management

The first priority is respiratory and supportive care.

Important measures include:

• Frequent neurologic reassessment
• Close respiratory monitoring
• Cardiac monitoring when autonomic instability is possible
• Early airway support when respiratory or bulbar weakness progresses
• Identification and treatment of the underlying cause

Patients with significant progressive ascending paralysis generally require hospital admission and close monitoring, often in an intensive-care setting.

Cause-Specific Treatment

GBS

• IV immunoglobulin (IVIG) or
• Plasma exchange

Both are established disease-modifying treatments. Corticosteroids alone are not effective treatment for typical GBS.

Tick paralysis

• Locate and completely remove the tick.
• Continue respiratory support when necessary.

AIP

• Remove precipitating factors.
• Provide supportive care.
• Intravenous hemin is the major specific therapy for significant acute attacks.
• Carbohydrate supplementation may be useful in selected mild attacks but should not delay hemin when significant neurologic disease is present.

Heavy-metal poisoning

• Remove the exposure.
• Appropriate chelation may be indicated depending on the metal and severity.

Tetrodotoxin

• No established specific antidote.
• Treatment is primarily meticulous supportive and respiratory care.

Decontamination

Older references recommended routine gastric lavage for some toxic ingestions. This is not standard modern practice.

Activated charcoal may occasionally be considered after an appropriate recent ingestion when the substance is adsorbed by charcoal and the airway is adequately protected.

Decontamination should never delay stabilization of airway, breathing, and circulation.

Key Points

• Ascending paralysis = weakness beginning in the legs and progressing upward.
• GBS is the major common cause and typically produces symmetric weakness with reduced or absent reflexes.
• Tick paralysis can closely resemble GBS; examine the entire skin and scalp.
• Tetrodotoxin blocks voltage-gated sodium channels and can rapidly cause paralysis and respiratory failure.
• Severe arsenic poisoning can produce a painful peripheral neuropathy with progressive weakness.
• Botulism usually causes descending, not ascending, paralysis.
• Albuminocytologic dissociation supports GBS, but it may be absent early.
• Respiratory deterioration can occur before major abnormalities appear on pulse oximetry.
• Progressive bulbar or respiratory weakness requires early airway planning and intensive monitoring.

Toxicology – Anticholinergic Syndrome

Definition

Anticholinergic syndrome is a toxidrome caused primarily by blockade of muscarinic acetylcholine receptors.

The classic presentation includes:

• Tachycardia
• Mydriasis and blurred vision
• Dry mouth and mucous membranes
• Warm, dry, flushed skin
• Decreased bowel sounds or ileus
• Urinary retention
• Agitation, delirium, and hallucinations
• Hyperthermia in more severe cases

Mechanism of Action

Antimuscarinic agents competitively inhibit acetylcholine at postsynaptic muscarinic receptors.

This reduces parasympathetic activity in the:

• Heart
• Eyes
• Sweat and salivary glands
• GI tract
• Urinary tract
• Central nervous system

Classic antimuscarinic agents do not primarily block nicotinic acetylcholine receptors.

Common Causes

Important causes include:

• First-generation antihistamines, especially diphenhydramine
• Tricyclic antidepressants
• Atropine
• Scopolamine
• Benztropine
• Oxybutynin
• Cyclobenzaprine
• Some antipsychotics
• Anticholinergic plants such as Datura and Atropa species
• Ophthalmic antimuscarinic agents

Some of these drugs have additional toxic actions. For example, severe diphenhydramine or TCA poisoning can also produce sodium-channel blockade and QRS widening.

Classic Toxidrome

A traditional mnemonic describes the syndrome as:

• “Mad as a hatter” → delirium, agitation, hallucinations
• “Hot” → hyperthermia
• “Dry as a bone” → dry skin and mucous membranes
• “Blind as a bat” → mydriasis and impaired accommodation
• “Red as a beet” → flushed skin

Not every patient develops every feature.

Vital Signs

Tachycardia is common because muscarinic blockade reduces vagal influence on the heart.

Other findings may include:

• Mild-to-moderate hyperthermia
• Hypertension from agitation
• Tachypnea
• Hypotension in severe poisoning or after seizures

HEENT

Common findings:

• Mydriasis
• Blurred vision
• Dry mouth
• Reduced secretions

Local ocular exposure can cause isolated mydriasis or anisocoria.

Skin

Typical findings are:

• Warm
• Dry
• Flushed

Reduced sweating contributes to hyperthermia.

Gastrointestinal and Genitourinary

Muscarinic blockade decreases smooth-muscle activity and secretions.

This can produce:

• Reduced bowel sounds
• Constipation
• Ileus
• Urinary retention
• Bladder distension

Neurologic Features

Central antimuscarinic toxicity may cause:

• Restlessness
• Agitation
• Confusion
• Disorientation
• Paranoia
• Visual hallucinations
• Delirium

Severe poisoning may cause:

• Seizures
• Marked hyperthermia
• Coma

Severe agitation or seizures can also produce rhabdomyolysis.

Anticholinergic vs. Sympathomimetic Toxidrome

These syndromes overlap because both can cause:

• Tachycardia
• Hypertension
• Mydriasis
• Hyperthermia
• Agitation
• Delirium

A useful distinction is the skin and GI examination:

Anticholinergic

• Dry skin
• Dry mouth
• Reduced bowel sounds
• Urinary retention

Sympathomimetic

• Diaphoresis
• Bowel sounds usually preserved or increased

Diagnosis

Diagnosis is primarily clinical, based on the toxidrome and exposure history.

Useful investigations in moderate or severe cases may include:

• ECG
• Electrolytes
• Renal function
• Glucose
• Creatine kinase when severe agitation, seizures, or hyperthermia raise concern for rhabdomyolysis
• Targeted testing for important possible coingestants

An ECG is particularly important because some anticholinergic drugs also produce cardiac sodium-channel blockade.

Management

Treatment is primarily supportive.

Important measures include:

• Airway and respiratory support when necessary
• IV fluids when clinically indicated
• External cooling for significant hyperthermia
• Cardiac monitoring in significant poisoning
• Monitoring for urinary retention
• Treatment of complications such as seizures and rhabdomyolysis

Benzodiazepines are commonly used for significant agitation and seizures.

Routine induction of vomiting and gastric lavage, as recommended in older references, are not standard modern management because their risks generally outweigh their benefits.

Activated charcoal may be considered after selected substantial recent ingestions when the airway can be safely protected.

Physostigmine

Physostigmine is a reversible acetylcholinesterase inhibitor that crosses the blood-brain barrier and can reverse both central and peripheral antimuscarinic effects.

It may be considered for severe, clinically significant antimuscarinic delirium in carefully selected patients.

It should not be treated as a routine diagnostic test for unexplained altered mental status.

Important precautions include avoiding its use when:

• TCA or another sodium-channel-blocking overdose is suspected
• The ECG shows concerning conduction abnormalities such as significant QRS widening
• The poisoning is not clearly compatible with a predominantly antimuscarinic syndrome

Because inappropriate or rapid administration can cause bradycardia, cholinergic effects, seizures, or dysrhythmias, its use requires appropriate monitoring and toxicology expertise.

Expected Course

Symptoms may develop gradually because antimuscarinic effects can slow gastrointestinal motility and delay absorption.

Many uncomplicated cases resolve within approximately a day, although severe poisoning or long-acting agents can cause symptoms lasting considerably longer.

Key Points

• Anticholinergic toxicity is primarily muscarinic receptor blockade.
• Classic findings are tachycardia + mydriasis + dry/flushed skin + decreased bowel sounds + urinary retention + delirium.
• Dry skin helps distinguish anticholinergic toxicity from the usually sweaty sympathomimetic toxidrome.
• Severe toxicity can cause hyperthermia, seizures, rhabdomyolysis, and coma.
• ECG assessment is important because some causative drugs have additional cardiotoxic effects.
• Benzodiazepines and supportive care are central to treatment.
• Physostigmine can rapidly reverse severe antimuscarinic delirium in appropriately selected patients, but it requires careful screening for contraindications.
• Older recommendations for routine ipecac or gastric lavage are obsolete.

Ophthalmology – Unexplained High-Anion-Gap Metabolic Acidosis

What the Disorder Represents

High-anion-gap metabolic acidosis (HAGMA) is a metabolic acid-base disturbance caused by accumulation of acids whose accompanying anions are not routinely measured on the standard electrolyte panel.

The basic calculation is:

Anion gap = Na⁺ − (Cl⁻ + HCO₃⁻)

The key clinical question is not simply whether bicarbonate is low, but:

Why has an unmeasured acid accumulated?

This can represent a life-threatening emergency from:

• Lactic acidosis
• Ketoacidosis
• Renal failure
• Toxic alcohol poisoning
• Salicylate poisoning
• Other severe toxic or metabolic disorders

Important Modern Correction: Metabolic Acidosis Is Not Defined by Bicarbonate Alone

A serum bicarbonate below 24 mEq/L does not by itself prove metabolic acidosis.

True metabolic acidosis is characterized by:

• Reduced serum bicarbonate
• Appropriate acidemia or compensatory respiratory response

The blood pH may occasionally be normal when another simultaneous acid-base disorder is present.

A blood gas and clinical context are therefore important.

Why an Anion Gap Exists

Plasma must remain electrically neutral.

Routine chemistry measures only some ions:

Measured Cation

• Sodium

Measured Anions

• Chloride
• Bicarbonate

Important unmeasured anions include:

• Albumin
• Phosphate
• Sulfate
• Organic acids

The normal apparent gap largely reflects:

Negatively charged albumin.

What Is a Normal Anion Gap?

The normal range depends on:

• Laboratory methodology
• Electrolyte analyzer
• Albumin concentration

With modern assays, a typical reference range without potassium is approximately:

8–12 mEq/L

rather than the older universal cutoff of <16 mEq/L.

Always use the:

Local laboratory reference range.

Correcting the Gap for Albumin

Hypoalbuminemia can conceal a dangerous high-anion-gap acidosis.

A commonly used correction is:

Corrected AG = measured AG + 2.5 × (4 − serum albumin in g/dL)

For example, an apparently normal gap in a severely hypoalbuminemic ICU patient may actually represent:

Significant accumulation of unmeasured acid.

The Modern Differential: GOLD MARK

The older MUDPILES mnemonic is historically useful but includes obsolete causes such as phenformin and paraldehyde.

A more useful modern mnemonic is:

GOLD MARK

• G – Glycols: ethylene glycol, propylene glycol
• O – Oxoproline (5-oxoproline/pyroglutamic acidosis)
• L – L-lactic acidosis
• D – D-lactic acidosis
• M – Methanol
• A – Aspirin/salicylates
• R – Renal failure
• K – Ketoacidosis

This should be combined with the patient’s clinical circumstances rather than used mechanically.

The Most Common Cause: Lactic Acidosis

Elevated lactate is among the most common causes of HAGMA.

Lactate accumulation may result from:

• Shock
• Sepsis
• Severe hypoxemia
• Tissue ischemia
• Cardiac arrest
• Generalized seizures
• Extreme agitation
• Severe anemia
• Mesenteric or limb ischemia

Drug- and toxin-related causes include:

• Metformin in susceptible patients
• Cyanide
• Carbon monoxide
• Propofol infusion syndrome
• Some antiretroviral drugs
• Beta-adrenergic stimulation

Type A vs Type B Lactic Acidosis

Type A

Caused primarily by impaired tissue oxygen delivery or utilization, such as:

• Shock
• Hypoxemia
• Severe ischemia

Type B

Occurs without obvious systemic hypoperfusion and may result from:

• Drugs
• Liver dysfunction
• Malignancy
• Thiamine deficiency
• Mitochondrial dysfunction

This distinction can help guide investigation.

Ketoacidosis

Important causes include:

• Diabetic ketoacidosis (DKA)
• Alcoholic ketoacidosis
• Starvation ketoacidosis
• SGLT2 inhibitor–associated euglycemic DKA

The most useful ketone assay is:

Serum beta-hydroxybutyrate.

Urine ketone strips primarily detect acetoacetate and may substantially underestimate early DKA.

Euglycemic Ketoacidosis

Do not exclude DKA solely because the glucose is not markedly elevated.

SGLT2 inhibitors can produce significant ketoacidosis with:

• Normal
• Mildly elevated

blood glucose.

A high gap with unexplained nausea, abdominal symptoms, or tachypnea in such a patient should prompt:

Beta-hydroxybutyrate testing.

Renal Failure

Advanced kidney failure causes accumulation of:

• Sulfate
• Phosphate
• Organic acids

producing:

High-anion-gap metabolic acidosis.

Earlier chronic kidney disease may instead produce a predominantly:

Normal-anion-gap acidosis.

Methanol Poisoning

Methanol is particularly important in ophthalmology because its toxic metabolite:

Formic acid

can damage the:

• Retina
• Optic nerve
• CNS

Methanol poisoning classically causes:

High-anion-gap metabolic acidosis + visual toxicity.

Ocular Clues to Methanol Poisoning

Patients may report:

• Blurred vision
• “Snowfield” vision
• Photophobia
• Central visual loss
• Dyschromatopsia
• Complete blindness in severe poisoning

Examination may reveal:

• Reduced acuity
• RAPD if asymmetric
• Optic disc hyperemia or edema early
• Subsequent optic atrophy

Unexplained visual symptoms combined with severe metabolic acidosis should immediately raise concern for:

Methanol exposure.

Ethylene Glycol Poisoning

Ethylene glycol is metabolized to toxic acids including:

• Glycolic acid
• Oxalic acid

It can cause:

• Severe metabolic acidosis
• CNS depression
• Hypocalcemia
• Acute kidney injury

Calcium oxalate crystals may appear in urine but:

Their absence does not exclude poisoning.

Salicylate Poisoning

Salicylate toxicity classically produces a:

Mixed acid-base disorder.

Early:

Respiratory alkalosis

from direct respiratory-center stimulation.

Later:

High-anion-gap metabolic acidosis

from organic acid accumulation.

Therefore a near-normal pH can conceal severe toxicity because the two processes may offset each other.

Salicylate Clinical Clues

Important features include:

• Tinnitus
• Tachypnea
• Nausea/vomiting
• Diaphoresis
• Fever
• Agitation
• Delirium

Severe poisoning can cause:

• Pulmonary edema
• Seizures
• Coma

A serum salicylate concentration should be measured when the cause of HAGMA is unexplained.

Isoniazid

Isoniazid overdose can produce:

• Refractory seizures
• Lactic acidosis
• Coma

The specific antidote is:

Pyridoxine (vitamin B6).

Persistent seizures after suspected isoniazid ingestion are a major diagnostic clue.

Iron Poisoning

Severe iron toxicity can produce:

• Vomiting
• Hematemesis
• Abdominal pain
• Shock
• HAGMA
• Hepatic failure

A serum iron concentration and toxicology consultation are appropriate when suspected.

Acetaminophen and the Anion Gap

Two different mechanisms are relevant.

Massive Acute Overdose

May produce early:

Lactic acidosis

from mitochondrial dysfunction.

Repeated or Chronic Exposure in Susceptible Patients

Can cause:

5-oxoproline (pyroglutamic) acidosis

particularly with:

• Malnutrition
• Sepsis
• Renal dysfunction
• Chronic illness

This is the O in GOLD MARK.

Toluene

Toluene exposure may cause acidosis, especially in solvent abuse.

However, the classic disturbance is often:

Hyperchloremic normal-anion-gap metabolic acidosis

because hippurate is rapidly excreted with sodium and potassium.

An elevated gap may occur earlier or with severe exposure.

Carbon Monoxide and Cyanide

Both can produce:

Lactic acidosis through impaired cellular oxygen utilization.

Carbon Monoxide

May cause:

• Headache
• Confusion
• Syncope
• Chest pain

Pulse oximetry can be misleading.

Diagnosis relies on:

Carboxyhemoglobin measurement by co-oximetry.

Cyanide

Can cause:

• Abrupt cardiovascular collapse
• Severe lactic acidosis
• Altered mental status

A very high unexplained lactate in the appropriate exposure setting should raise concern.

Do Not Depend on Characteristic Odors

Older descriptions emphasize:

• Bitter almonds for cyanide
• Rotten eggs for hydrogen sulfide

These are unreliable because:

• Many individuals cannot detect them
• Odor may disappear rapidly
• Exposure itself may impair olfaction

Diagnosis should not depend on smell.

The Osmolal Gap

The osmolal gap is useful when toxic alcohol exposure is suspected.

It is:

Measured serum osmolality − calculated serum osmolality.

A commonly used calculation in conventional US units is:

Calculated osmolality ≈ 2 × Na + glucose/18 + BUN/2.8 + ethanol/4.6

Exact formulas vary.

Why Toxic Alcohols Produce an Osmolal Gap

Methanol and ethylene glycol themselves are:

Osmotically active parent alcohols.

Soon after ingestion:

• Osmolal gap rises
• Anion gap may still be normal

As metabolism proceeds:

• Parent alcohol concentration falls
• Osmolal gap may normalize
• Toxic organic acids accumulate
• Anion gap rises

Thus the two gaps can evolve in opposite directions.

A Normal Osmolal Gap Does Not Exclude Toxic Alcohol Poisoning

This is a critical principle.

A patient presenting late after methanol or ethylene glycol ingestion may have:

• Severe HAGMA
• Organ toxicity
• Normal or minimally increased osmolal gap

because the parent alcohol has already been converted to acidic metabolites.

First-Line Laboratory Evaluation

In unexplained HAGMA, useful initial tests generally include:

• Repeat serum electrolytes
• Glucose
• Creatinine and BUN
• Serum lactate
• Serum beta-hydroxybutyrate
• Blood gas
• Serum osmolality
• Salicylate level
• Acetaminophen level

Additional testing should be guided by the clinical context.

Venous vs Arterial Blood Gas

For most metabolic acid-base assessment:

Venous blood gas is usually adequate

for evaluating:

• pH
• Bicarbonate
• PCO₂ trend

Arterial sampling is more useful when precise assessment of:

Oxygenation

is needed.

Toxic Alcohol Levels

When available, directly measure:

• Methanol
• Ethylene glycol

But treatment should not be delayed while awaiting these levels when clinical suspicion is high.

Urinalysis

Useful findings may include:

• Ketones
• Glucose
• Hematuria
• Myoglobin
• Oxalate crystals

But urinary calcium oxalate crystals in ethylene glycol poisoning have:

Insufficient sensitivity to exclude poisoning when absent.

ECG

Obtain an ECG when overdose is possible.

It can reveal:

• QRS prolongation
• QT prolongation
• Dysrhythmias
• Ischemic changes

that may identify otherwise unsuspected cardiotoxic ingestion.

Assessing Respiratory Compensation

A patient with metabolic acidosis should compensate by lowering PCO₂.

Expected PCO₂ can be estimated using:

Winter’s formula:

Expected PCO₂ = 1.5 × HCO₃⁻ + 8 ± 2

If measured PCO₂ is:

• Higher than expected → additional respiratory acidosis
• Lower than expected → additional respiratory alkalosis

This is especially important in poisoned patients.

Why Respiratory Compensation Matters

A severely acidotic patient may be sustaining life by maintaining:

Very high minute ventilation.

Loss of that compensation during:

• Sedation
• Intubation
• Mechanical ventilation

can cause a sudden rise in PCO₂ and a catastrophic fall in pH.

This is especially dangerous in:

Salicylate poisoning.

Delta Gap and Mixed Metabolic Disorders

A high anion gap does not exclude a second metabolic disorder.

Comparing the increase in anion gap with the fall in bicarbonate can identify:

• Concurrent normal-gap acidosis
• Concurrent metabolic alkalosis

A commonly used concept is the:

Delta ratio.

This is useful in complicated ICU or toxicology cases but should be interpreted alongside the clinical picture.

Initial Management Priorities

Management begins with:

1. Airway and breathing when necessary
2. Circulatory support
3. Correction of hypoxemia
4. Identification of the acid source
5. Specific antidotal therapy when indicated
6. Serial reassessment

The underlying cause must be treated rather than simply correcting the laboratory bicarbonate value.

Important Modern Correction: The “Coma Cocktail” Is Obsolete

Older protocols routinely gave:

• Oxygen
• Thiamine
• Glucose
• Naloxone

to any patient with altered mental status.

Modern therapy is targeted.

Use:

• Glucose for documented or strongly suspected hypoglycemia
• Naloxone for suspected opioid-induced respiratory depression
• Thiamine in patients at risk of deficiency
• Oxygen for hypoxemia or carbon monoxide poisoning

Do not delay glucose in a hypoglycemic patient while waiting to administer thiamine.

Fomepizole for Toxic Alcohol Poisoning

Fomepizole inhibits alcohol dehydrogenase and prevents conversion of:

• Methanol → formic acid
• Ethylene glycol → glycolic/oxalic acids

It is the preferred antidote when toxic alcohol poisoning is suspected.

Do Not Wait for Confirmation

If there is a credible toxic alcohol exposure plus findings such as:

• Unexplained HAGMA
• Elevated osmolal gap
• Visual symptoms
• Acute kidney injury

Start fomepizole while confirmatory testing is pending.

Delaying treatment can cause irreversible:

• Blindness
• Renal failure
• Death

Ethanol as an Antidote

Ethanol also competes for alcohol dehydrogenase.

It remains an alternative when:

Fomepizole is unavailable.

However, fomepizole is preferred because ethanol is harder to dose and causes:

• Intoxication
• Hypoglycemia
• CNS depression
• Monitoring difficulties

Hemodialysis for Toxic Alcohols

Hemodialysis rapidly removes:

• Parent toxic alcohol
• Toxic metabolites

and corrects severe acidosis.

It should be considered in methanol or ethylene glycol poisoning with features such as:

• Severe metabolic acidosis
• Significant end-organ toxicity
• Visual toxicity from methanol
• Acute kidney injury from ethylene glycol
• Very high toxic alcohol concentration
• Clinical deterioration despite antidote

Exact thresholds depend on current toxicology protocols.

Folate Therapy in Methanol Poisoning

Folinic acid or folic acid may be administered because it facilitates metabolism of:

Formate to nontoxic products.

It is adjunctive to:

• Fomepizole
• Acidosis management
• Dialysis when indicated

Pyridoxine and Thiamine in Ethylene Glycol

Pyridoxine and thiamine are sometimes given as adjuncts to promote metabolism toward:

Less toxic metabolites.

They do not replace:

• Fomepizole
• Dialysis when indicated

Sodium Bicarbonate

Bicarbonate is not routine treatment for every lactic acidosis.

The priority is correcting the underlying:

• Shock
• Hypoxia
• Sepsis
• Ischemia

However, bicarbonate has important roles in selected severe acid-base disorders and toxicologic emergencies.

When Bicarbonate Is Particularly Important

Examples include:

• Salicylate poisoning, where serum and urinary alkalinization reduces tissue penetration and enhances elimination
• Severe methanol poisoning with marked acidemia
• Severe ethylene glycol poisoning with marked acidemia
• Selected cases of profound acidemia with cardiovascular instability

Use should be guided by the specific disorder.

Salicylate Alkalinization

In significant salicylate toxicity:

IV sodium bicarbonate is used to alkalinize serum and urine.

Increasing blood pH reduces movement of salicylate into:

• Brain
• Other tissues

Urinary alkalinization also increases salicylate excretion.

Intubation in Salicylate Poisoning

Intubation can be dangerous because even brief hypoventilation causes:

• Rising PCO₂
• Falling pH
• Increased nonionized salicylate
• Increased CNS penetration

If intubation is unavoidable:

Maintain or exceed the patient’s pre-intubation minute ventilation as closely as possible.

Decontamination – Major Modern Correction

Induced emesis is not recommended.

Routine gastric lavage is also:

Not recommended.

Gastric lavage is now reserved for exceptional, potentially lethal ingestions when:

• Presentation is very early
• The airway is protected
• Expert toxicology guidance supports it

Activated Charcoal

A single dose of activated charcoal may be considered when:

• The ingestion is potentially toxic
• The substance binds charcoal
• Presentation is sufficiently early
• Airway protection is adequate

It is not useful for all toxicants.

Substances Poorly Adsorbed by Activated Charcoal

Activated charcoal is generally ineffective for substances such as:

• Methanol
• Ethylene glycol
• Iron
• Lithium
• Many caustics

Therefore charcoal should not delay specific treatment for these exposures.

Why Persistent HAGMA Requires Escalation

Persistent unexplained HAGMA may represent:

• Occult shock
• Mesenteric ischemia
• Toxic alcohol poisoning
• Salicylate toxicity
• Ketoacidosis
• Severe renal failure

A patient whose gap remains elevated or continues rising requires:

Repeated investigation rather than passive observation.

Serial Monitoring

Depending on severity, follow:

• Electrolytes
• Anion gap
• Blood gas
• Lactate
• Glucose
• Beta-hydroxybutyrate
• Renal function
• Osmolality

Toxin concentrations should be repeated when clinically appropriate.

When Critical Care Is Needed

ICU-level management should be considered for:

• Severe acidemia
• Hemodynamic instability
• Altered mental status
• Respiratory compromise
• Seizures
• Suspected toxic alcohol poisoning
• Severe salicylate poisoning
• Need for dialysis

Persistent unexplained HAGMA generally warrants:

Hospital admission and continued evaluation.

Common Diagnostic Pitfalls

Important errors include:

• Using a fixed AG >16 threshold regardless of laboratory reference range
• Failing to correct the gap for low albumin
• Assuming a normal osmolal gap excludes toxic alcohol poisoning
• Missing euglycemic DKA
• Failing to obtain a salicylate concentration
• Attributing all lactate elevation to sepsis without considering toxins or ischemia
• Treating the bicarbonate number instead of the underlying disorder
• Intubating a profoundly acidotic patient without preserving compensatory ventilation

Ophthalmic Red Flag

The most important ophthalmic association is:

Methanol toxicity.

The combination of:

• Unexplained high-anion-gap metabolic acidosis
• Possible toxic alcohol exposure
• Acute bilateral visual blurring or visual loss

should trigger immediate treatment for suspected methanol poisoning while definitive levels are pending.

Optic nerve injury can become:

Irreversible.

High-Yield Takeaways

• High-anion-gap metabolic acidosis reflects accumulation of unmeasured acids and can indicate a life-threatening metabolic or toxicologic emergency.
• Calculate the gap as Na − (Cl + HCO₃), but use the laboratory’s own normal range rather than an outdated universal cutoff of 16 mEq/L.
• Correct the anion gap for hypoalbuminemia, approximately adding 2.5 mEq/L for every 1 g/dL that albumin is below 4 g/dL.
• The modern differential is summarized by GOLD MARK: Glycols, Oxoproline, L-lactate, D-lactate, Methanol, Aspirin, Renal failure, Ketoacidosis.
• Lactic acidosis, ketoacidosis, and renal failure are among the most common causes.
• Salicylate poisoning classically causes respiratory alkalosis plus high-anion-gap metabolic acidosis.
• Measure beta-hydroxybutyrate when ketoacidosis is suspected; urine ketones may underestimate early disease.
• SGLT2 inhibitors can cause euglycemic DKA, so a normal glucose does not exclude ketoacidosis.
• Methanol causes formate toxicity and optic neuropathy; visual symptoms plus HAGMA should be treated as methanol poisoning until proven otherwise.
• Ethylene glycol causes severe acidosis, hypocalcemia, and acute kidney injury; urinary oxalate crystals are supportive but not required.
• A high osmolal gap supports toxic alcohol exposure, but a normal osmolal gap does not exclude late methanol or ethylene glycol poisoning.
• Early toxic alcohol poisoning may have a high osmolal gap with little acidosis; later poisoning may have a high anion gap with a normalizing osmolal gap.
• Initial evaluation should usually include electrolytes, blood gas, lactate, beta-hydroxybutyrate, glucose, renal function, measured serum osmolality, salicylate level, and acetaminophen level.
• Use Winter’s formula to determine whether respiratory compensation is appropriate.
• Fomepizole is the preferred antidote for suspected methanol or ethylene glycol poisoning, and treatment should not wait for confirmatory levels when suspicion is high.
• Severe toxic alcohol poisoning may require urgent hemodialysis.
• Sodium bicarbonate is particularly important in salicylate toxicity and severe toxic-alcohol acidemia, but it is not routine treatment for every lactic acidosis.
• Induced emesis is obsolete, and gastric lavage is now extremely rarely indicated.
• Activated charcoal does not effectively adsorb methanol, ethylene glycol, iron, or lithium.
• The traditional indiscriminate “coma cocktail” is outdated; antidotes and supportive treatment should be targeted to the suspected problem.
• During intubation of a severely acidotic patient, preserve compensatory high minute ventilation; loss of hyperventilation can cause catastrophic acidemia, particularly in salicylate poisoning.
• Persistent, unexplained HAGMA warrants serial reassessment, hospital admission, and early toxicology/nephrology involvement when indicated.

High-Yield Takeaways

Toxicology – Acute Kidney Injury (AKI) in Poisoning

Definition

Acute kidney injury (AKI), historically called acute renal failure, is an abrupt decline in renal function resulting in impaired regulation of fluid, electrolytes, acid-base balance, and waste products.

Related terms:

• Azotemia: increased BUN and/or serum creatinine
• Acute tubular injury/necrosis (ATI/ATN): damage and dysfunction of renal tubular cells
• Acute interstitial nephritis (AIN): inflammatory injury involving the renal interstitium
• Nephrotic syndrome: heavy proteinuria associated with hypoalbuminemia, edema, and often hyperlipidemia

Major Mechanisms

Toxin-associated AKI can be divided into three broad categories:

1. Prerenal AKI – decreased renal perfusion

• Dehydration
• Vomiting or diarrhea
• Hemorrhage
• Hypotension or shock
• Drug-induced cardiac dysfunction
• Altered renal vascular tone

Examples of drugs that can impair renal perfusion include NSAIDs, ACE inhibitors, and calcineurin inhibitors.

2. Intrinsic Renal Injury – direct kidney damage

Important mechanisms include:

• Acute tubular injury
• Acute interstitial nephritis
• Glomerular injury
• Pigment nephropathy from rhabdomyolysis or hemolysis
• Crystal nephropathy

Representative nephrotoxic exposures include:

• Aminoglycosides
• Amphotericin B
• Cisplatin
• Cyclosporine
• Ethylene glycol
• Methotrexate
• Heavy metals
• Certain mushrooms
• Radiographic contrast in susceptible patients

3. Postrenal AKI – urinary obstruction

Possible causes include:

• Drug or metabolite crystallization
• Calcium or uric acid stones
• Anticholinergic urinary retention
• Other mechanical urinary obstruction

Risk Factors

The risk of toxin-associated AKI increases with:

• Pre-existing kidney disease
• Dehydration or hypovolemia
• Simultaneous exposure to several nephrotoxic agents
• Severe systemic poisoning
• Prolonged hypotension

Clinical Features

AKI may initially produce few symptoms.

Possible findings include:

• Reduced urine output
• Fluid retention
• Peripheral or pulmonary edema
• Hypertension
• Nausea and vomiting
• Weakness
• Confusion in severe uremia

Major complications include:

• Hyperkalemia
• Metabolic acidosis
• Fluid overload
• Uremia

Urine output can be reduced, normal, or occasionally increased, so normal urine production does not exclude AKI.

Toxicologic Clues

Certain findings can suggest the underlying exposure:

• Anion-gap metabolic acidosis + calcium oxalate crystalluria → ethylene glycol
• Rhabdomyolysis → sympathomimetics, prolonged coma/immobility, seizures, carbon monoxide, and several other toxic exposures
• Microcytic anemia + basophilic stippling → chronic lead exposure
• GI injury + renal failure → consider heavy metals and other systemic toxicants
• Tremor, neurologic abnormalities + renal dysfunction → consider lithium in the appropriate setting

These findings are clues rather than diagnostic by themselves.

Urinalysis and Urine Sediment

Urine microscopy can help determine the mechanism of renal injury.

Prerenal AKI

• Often relatively bland urine sediment
• Hyaline casts may occur

Acute tubular injury

• Muddy-brown granular casts
• Renal tubular epithelial cells

Glomerulonephritis

• Hematuria
• Proteinuria
• Red blood cell casts

Pigment nephropathy

• Urine dipstick positive for blood with few or no red blood cells on microscopy suggests myoglobin or free hemoglobin

Crystal nephropathy

• Calcium oxalate crystals may support ethylene glycol exposure in the appropriate clinical setting.
• Uric acid crystals can occur with uric acid nephropathy.

Laboratory Evaluation

Important tests may include:

• Serum creatinine and BUN
• Electrolytes
• Bicarbonate
• Calcium, magnesium, and phosphate
• Urinalysis with microscopy
• Urine output monitoring
• Creatine kinase when rhabdomyolysis is suspected
• ECG when hyperkalemia is possible
• Targeted toxicant concentrations when clinically indicated

Serial creatinine measurements are often more informative than a single value because creatinine may rise after the kidney injury has already occurred.

FENa and Other Urine Indices

Traditionally:

• Low fractional excretion of sodium (FENa) supports a prerenal process.
• Higher FENa may support intrinsic tubular injury.

However, these are supportive rather than definitive tests. Diuretics, chronic kidney disease, sepsis, and several other conditions can make FENa misleading.

Clinical context and urine sediment are therefore important.

Management

Treatment focuses on both the cause of AKI and its complications:

• Stop nephrotoxic substances when possible.
• Treat the underlying poisoning.
• Restore appropriate intravascular volume when hypovolemia is present.
• Maintain adequate renal perfusion.
• Carefully monitor fluid intake and urine output.
• Correct clinically important electrolyte and acid-base abnormalities.
• Treat rhabdomyolysis or other underlying causes when present.

A specific antidote should be given when one exists for the responsible toxicant.

Dialysis

Renal replacement therapy may be required for complications such as:

• Refractory hyperkalemia
• Severe metabolic acidosis
• Pulmonary edema or fluid overload
• Significant uremic complications

In toxicology, dialysis may also be indicated specifically to remove a dialyzable poison, such as lithium, methanol, ethylene glycol, or salicylate, even before conventional indications for dialysis develop.

Important Modern Correction

Older references sometimes recommend “renal-dose” dopamine to preserve kidney function.

This practice is no longer recommended because low-dose dopamine has not been shown to prevent or treat AKI and can cause adverse effects.

Loop diuretics may help manage volume overload, but they do not reverse intrinsic kidney injury or improve renal recovery simply by increasing urine output.

Key Points

• Toxin-related AKI may be prerenal, intrinsic renal, or postrenal.
• Muddy-brown granular casts → acute tubular injury.
• RBC casts → glomerular disease.
• Positive urine blood with few/no RBCs → consider myoglobinuria or hemoglobinuria.
• Hyperkalemia, metabolic acidosis, and fluid overload are major complications.
• Creatinine may lag behind the actual renal injury.
• FENa can support the diagnosis but should not be interpreted in isolation.
• Treat the underlying poisoning and discontinue nephrotoxins whenever possible.
• “Renal-dose” dopamine should not be used to prevent or treat AKI.

Toxicology – Drug Screening

Definition

Drug screening detects selected drugs or their metabolites in urine or blood.

In toxicology, drug screens are mainly an adjunct to the history, physical examination, vital signs, ECG, and targeted laboratory testing. They should not replace recognition of the patient’s clinical toxidrome.

The substances included in a drug screen vary considerably between laboratories.

Urine Drug Screening

Urine is commonly used because many drugs and their metabolites become concentrated in urine and remain detectable longer than in blood.

The major testing methods are:

• Immunoassay
• Chromatographic techniques
• Mass spectrometry for more definitive identification

Immunoassay

Mechanism

Antibodies recognize a particular drug or drug class. The resulting reaction is detected using an enzymatic or other laboratory method.

Advantages

• Rapid
• Relatively inexpensive
• Minimal specimen preparation
• Widely available

Limitations

• Detects only substances included in the assay
• Cross-reactivity can produce false-positive results
• Some members of a drug class may not be detected, producing false-negative results

For example, a routine opioid immunoassay may fail to detect certain synthetic or semisynthetic opioids unless specific assays are ordered.

Chromatography

Chromatographic methods separate substances according to their chemical properties.

Techniques include:

• Gas chromatography
• Liquid chromatography

These methods can identify a broader range of compounds than many routine immunoassays but generally require more specialized equipment and expertise.

Mass Spectrometry

Mass spectrometry is commonly combined with chromatography, such as:

• GC-MS: gas chromatography–mass spectrometry
• LC-MS/MS: liquid chromatography–tandem mass spectrometry

The technique identifies compounds based on characteristic molecular properties and provides much greater specificity than routine immunoassay screening.

It is particularly useful when definitive identification is required, although availability and turnaround time vary.

Targeted Serum Testing

For many important poisonings, a specific quantitative blood concentration is more useful than a broad urine drug screen.

Important examples include:

• Acetaminophen
• Salicylates
• Lithium
• Ethanol
• Methanol
• Ethylene glycol
• Selected anticonvulsants
• Theophylline

The appropriate test depends on the suspected exposure.

Clinical Uses

Routine broad toxicology screening is usually unnecessary in a patient whose history and clinical findings already establish the diagnosis.

Testing may be useful when:

• Altered mental status has no clear explanation.
• The reported ingestion does not match the clinical findings.
• Multiple or unknown substances may have been involved.
• Definitive identification would meaningfully change management.

The clinician should ideally know how the result will affect treatment before ordering the test.

Interpreting a Positive Result

A positive urine drug screen indicates that the assay detected a drug, metabolite, or cross-reacting substance.

It does not necessarily prove:

• Current intoxication
• The dose taken
• When the substance was used
• That the detected drug caused the patient’s current symptoms

Many substances remain detectable in urine after their clinical effects have resolved.

Interpreting a Negative Result

A negative drug screen does not exclude poisoning.

Possible explanations include:

• The drug is not included in the panel.
• The concentration is below the assay’s detection threshold.
• The specimen was collected too early.
• The urine is very dilute.
• The assay does not reliably detect that particular drug.
• The specimen was altered or substituted in nonclinical testing situations.

Therefore:

Negative screen ≠ no toxic exposure.

Important Limitations

Many clinically important toxicants are poorly assessed by routine urine drug screens and require specific testing or clinical diagnosis.

Examples include:

• Lithium
• Iron
• Heavy metals
• Toxic alcohols
• Cyanide
• Hydrocarbons

The exact limitations depend on the laboratory and assay being used.

Confirmatory Testing

When a screening result has major legal, occupational, forensic, or other consequences, an initial immunoassay result generally requires more specific confirmatory testing, commonly using mass-spectrometric techniques.

Key Points

• Treat the patient, not the drug screen.
• Urine immunoassays are convenient but have important false-positive and false-negative limitations.
• A positive urine result does not establish active intoxication.
• A negative result does not rule out poisoning.
• Targeted quantitative serum concentrations are more useful for several major toxicants.
• Always determine which substances the local laboratory panel actually detects.
• Drug screening is most valuable when the result can answer a specific clinical question or alter management.

Toxicology – Enhanced Elimination Techniques III

Peritoneal Dialysis

Mechanism of Action

Dialysis fluid is placed into the peritoneal cavity, and the peritoneal membrane acts as a semipermeable barrier.

Toxicants diffuse from the bloodstream into the dialysate, which is subsequently drained and replaced.

Substances are more readily removed when they are:

• Water soluble
• Minimally protein bound
• Low molecular weight
• Distributed mainly within the bloodstream

Potential Indications

Peritoneal dialysis has historically been used for selected severe poisonings, particularly when hemodialysis is unavailable or technically impossible.

Examples have included:

• Methanol
• Ethylene glycol
• Salicylates
• Theophylline

It has also been considered in infants or neonates when other extracorporeal techniques cannot be performed.

Current Role

Peritoneal dialysis removes most toxicants much more slowly than hemodialysis. Modern intermittent hemodialysis is therefore preferred for most poisonings requiring extracorporeal removal.

Complications

• Peritonitis
• Bowel or abdominal-organ injury
• Fluid and electrolyte abnormalities
• Hypotension
• Volume overload
• Catheter-related complications

Previous abdominal surgery or adhesions can make treatment technically difficult.

Key Point

Peritoneal dialysis now has a very limited role in poisoning and is generally considered only when more effective extracorporeal techniques are unavailable.

Urinary Alkalinization

Mechanism of Action

Urinary alkalinization increases urinary elimination of certain weak acids.

Increasing urine pH causes these substances to become more ionized within the renal tubule. The ionized molecules cannot readily diffuse back across cell membranes, producing “ion trapping” and increasing urinary excretion.

Major Indication

The most important toxicologic indication is:

• Salicylate poisoning

Urinary alkalinization increases renal salicylate elimination and also helps maintain alkalemia, which reduces movement of salicylate into tissues such as the brain.

Other substances whose elimination can theoretically or measurably increase include:

• Phenobarbital
• Chlorpropamide
• 2,4-D herbicides

However, clinical benefit is best established for salicylate toxicity.

Urine alkalinization is also used during high-dose methotrexate therapy to reduce renal precipitation and nephrotoxicity, although this is primarily an oncologic rather than poisoning indication.

Monitoring / Complications

Important problems include:

• Hypokalemia
• Metabolic alkalosis
• Volume overload
• Hypernatremia
• Hypomagnesemia

Adequate potassium is particularly important because hypokalemia makes successful urine alkalinization more difficult.

Patients with severe salicylate poisoning may require hemodialysis rather than alkalinization alone.

Key Point

Think of urinary alkalinization primarily as an enhanced elimination technique for salicylates.

Urinary Acidification

Mechanism of Action

Historically, urine was acidified in an attempt to increase elimination of weakly basic drugs through ion trapping.

Current Role

There are no routine toxicologic indications for urinary acidification.

Potential harms outweigh the limited improvement in drug elimination.

Complications can include:

• Systemic metabolic acidosis
• Worsening kidney injury
• Increased precipitation of myoglobin or hemoglobin within renal tubules
• Electrolyte disturbances

For this reason, urinary acidification is considered an obsolete enhanced-elimination technique.

Key Points

• Peritoneal dialysis: rarely used because hemodialysis generally clears toxicants more efficiently.
• Urinary alkalinization: particularly important for salicylate poisoning through ion trapping of weak acids.
• Urinary acidification: no longer recommended because its risks outweigh its benefits.
• Severe poisoning should not be managed according to pharmacokinetic principles alone; the patient’s clinical condition determines whether more definitive treatment such as hemodialysis is required.

Toxicology – Enhanced Elimination Techniques II

Hemofiltration

Mechanism of Action

Hemofiltration passes blood through a semipermeable membrane, removing water and dissolved substances by convection.

It can remove:

• Certain toxicants
• Electrolytes
• Urea and creatinine
• Some therapeutic medications

Continuous renal replacement techniques provide slower, prolonged clearance. Because treatment continues while a toxicant redistributes from tissues into the bloodstream, they may reduce post-treatment rebound.

Potential Indications

Hemofiltration may be considered for selected severe poisonings involving substances with:

• Relatively small volume of distribution
• Low endogenous clearance
• Suitable molecular size

It has occasionally been used for substances such as:

• Lithium
• Certain aminoglycosides

However, for many dialyzable poisons, intermittent hemodialysis provides substantially faster clearance and is preferred when the patient can tolerate it.

Advantages

• Continuous and gradual removal
• Better tolerated than intermittent hemodialysis in some hemodynamically unstable patients
• Useful when continuous renal replacement therapy is already required for renal failure

Limitations / Complications

• Slower toxicant clearance than conventional hemodialysis
• Fluid and electrolyte disturbances
• Vascular-access complications
• Bleeding or anticoagulation-related complications

Key Point

Modern continuous renal replacement therapy can be useful when conventional hemodialysis is poorly tolerated, but slower clearance makes it unsuitable as a direct substitute for rapid hemodialysis in many severe poisonings.

Multiple-Dose Activated Charcoal (MDAC)

Mechanism of Action

Multiple-dose activated charcoal involves repeated administration of charcoal to increase elimination of certain already-absorbed toxicants.

It works mainly through two mechanisms:

• Interrupting enterohepatic/enteric recycling: drugs secreted back into the GI tract are bound by charcoal before they can be reabsorbed.
• “Gastrointestinal dialysis”: some drugs diffuse from the bloodstream across the intestinal wall into the GI lumen, where charcoal traps them.

This maintains a concentration gradient favoring movement of the toxicant from blood into the intestine.

Best Candidates

MDAC is most effective for drugs that:

• Bind strongly to activated charcoal
• Have relatively small volumes of distribution
• Remain in the circulation long enough for enhanced GI elimination

The classic drugs for which MDAC may meaningfully enhance elimination include:

• Carbamazepine
• Dapsone
• Phenobarbital
• Quinine
• Theophylline

Enhanced elimination has been demonstrated for several other substances, but evidence that this improves clinical outcomes is more limited.

Contraindications

MDAC should generally be avoided with:

• Unprotected airway or high aspiration risk
• Ileus
• Bowel obstruction
• GI perforation

Complications

• Vomiting
• Aspiration pneumonitis
• Constipation
• Bowel obstruction or charcoal impaction
• Fluid and electrolyte disturbances, particularly when cathartics are repeatedly administered

Important Precaution

Repeated cathartic administration should be avoided because it can cause dangerous fluid and electrolyte losses, especially in children.

Key Points

• MDAC is an enhanced elimination technique, not simply repeated GI decontamination.
• Remember the classic MDAC drugs: carbamazepine, dapsone, phenobarbital, quinine, and theophylline.
• The airway must be protected before charcoal is considered in a patient with significant CNS depression.
• Ileus or bowel obstruction substantially increases the risk of complications.
• Continuous hemofiltration provides slower clearance than intermittent hemodialysis but may be useful when hemodynamic instability limits conventional dialysis.