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Emergency And Acute Medicine – Cyanide Poisoning
Overview
Cyanide toxicity occurs through inhalation or gastrointestinal absorption. Cyanide is an intracellular toxin that disrupts aerobic metabolism by inhibiting oxidative phosphorylation, resulting in impaired oxygen utilization and reduced ATP production. Detoxification primarily occurs via the hepatic mitochondrial enzyme rhodanese, which combines cyanide with sulfur in an irreversible reaction to form the less toxic, water-soluble thiocyanate. Cyanide can also bind hemoglobin to form reversible cyanhemoglobin or bind hydroxocobalamin to form nontoxic cyanocobalamin. Effective detoxification depends on adequate sulfur availability, particularly thiosulfate.
Causes And Sources
Cyanide exposure most commonly occurs during fires as a combustion by-product of natural and synthetic materials. Industrial sources include metal plating, microchip and plastic manufacturing, chemical synthesis, pesticides, and solvents such as artificial nail remover and metal polishes. Cyanide may also be produced during nitroprusside metabolism and by certain bacterial infections. Dietary sources include amygdalin-containing plants such as apricot pits, peach pits, apple seeds, pear seeds, and cassava. Jewelry making is another recognized exposure risk.
Clinical Features
The heart and brain are the most sensitive organs and are typically affected first. Neurologic manifestations include headache, confusion, syncope, seizures, and coma. Cardiovascular findings include dyspnea, chest pain, rapid progression to cardiorespiratory collapse, and death. Gastrointestinal symptoms such as nausea and vomiting may occur. Oral exposure can be caustic, with as little as 50 mg causing death. Inhalational exposure to 50 ppm may cause anxiety, palpitations, dyspnea, and headache, while concentrations of 100–135 ppm can be lethal in less than one hour.
Initial Evaluation
A history suggestive of smoke inhalation, industrial exposure, or intentional ingestion should raise suspicion. Classic findings such as the odor of bitter almonds or bright red retinal vessels are often absent. Key clinical clues include abrupt onset or rapid deterioration, severe lactic acidosis, and elevated venous oxygen saturation due to impaired cellular oxygen utilization, resulting in arterialized venous blood gases.
Diagnostic Studies
Laboratory evaluation typically includes complete blood count, metabolic panel, liver profile, creatine phosphokinase, carboxyhemoglobin, and methemoglobin levels. Cyanide levels are usually send-out tests and not available in real time; levels above 0.5–1 mg/L are toxic, and levels of 2.5–3 mg/L are often fatal. Blood gas analysis may show elevated mixed venous oxygen saturation, reduced arteriovenous oxygen difference, and markedly elevated lactate levels greater than 8 mmol/L, which serve as a useful surrogate marker when exposure history is consistent. Chest radiography may assist in evaluating concurrent inhalation injury.
Conditions To Differentiate
The differential diagnosis includes carbon monoxide poisoning, hydrogen sulfide exposure, methemoglobinemia, sulfhemoglobinemia, inert gas asphyxiation, and other causes of high anion gap metabolic acidosis.
Prehospital Management
Immediate removal from the source of exposure is critical, while preventing secondary contamination of rescuers. Contaminated clothing should be removed and bagged, and liquid exposures require thorough washing with soap and water. Vapor exposures may resolve with simple removal from the environment.
Emergency Stabilization
Initial management follows standard airway, breathing, and circulation principles. Administer 100% oxygen regardless of measured oxygen tension, as it acts synergistically with antidotes. Gastric lavage and activated charcoal may be considered for recent oral ingestion if no contraindications exist. Dermal exposures require standard decontamination measures.
Definitive Treatment
Hydroxocobalamin is the preferred first-line antidote for patients with significant toxicity, including persistent high anion gap metabolic acidosis, hyperlactatemia, seizures, syncope, dysrhythmias, or hypotension. It binds cyanide to form cyanocobalamin, which is renally excreted. Advantages include the absence of methemoglobinemia and hypotension. Limitations include cost, drug incompatibilities within IV lines, and interference with certain laboratory assays.
An alternative is the traditional cyanide antidote kit, which includes amyl nitrite, sodium nitrite, and sodium thiosulfate. Nitrites induce methemoglobinemia to sequester cyanide away from mitochondria, while sodium thiosulfate enhances enzymatic detoxification via rhodanese. Nitrites should not be used empirically and require caution due to the risk of excessive methemoglobinemia and hypotension. Hyperbaric oxygen therapy may be considered as adjunctive treatment to maximize tissue oxygenation.
Medication Summary
First-line therapy is hydroxocobalamin administered intravenously at weight-based dosing, with repeat dosing if necessary. Activated charcoal may be used for recent ingestions. Second-line therapy involves the cyanide antidote kit, including carefully dosed nitrites and sodium thiosulfate. Special dosing considerations apply in pediatric patients, pregnancy, and those with hepatic or renal impairment.
Disposition And Follow-Up
All symptomatic patients require intensive care unit admission. Asymptomatic patients may be discharged after at least four hours of observation if no symptoms develop, as survival beyond this period is usually associated with full recovery. Psychiatric evaluation is indicated for intentional exposures.
Key Clinical Insights And Common Errors
In patients presenting with hypotension, seizures, altered mental status, severe lactic acidosis, and high anion gap metabolic acidosis, cyanide poisoning should be strongly considered and treated empirically. Serum lactate is a valuable surrogate marker when exposure history is suggestive. Victims of smoke inhalation may have combined cyanide toxicity, carbon monoxide poisoning, and methemoglobinemia. When carbon monoxide levels are markedly elevated, concomitant cyanide exposure should be suspected. To avoid worsening oxygen delivery, initial treatment should prioritize hydroxocobalamin or sodium thiosulfate without nitrites when methemoglobinemia would be harmful.
Overview
Cyanide toxicity occurs through inhalation or gastrointestinal absorption. Cyanide is an intracellular toxin that disrupts aerobic metabolism by inhibiting oxidative phosphorylation, resulting in impaired oxygen utilization and reduced ATP production. Detoxification primarily occurs via the hepatic mitochondrial enzyme rhodanese, which combines cyanide with sulfur in an irreversible reaction to form the less toxic, water-soluble thiocyanate. Cyanide can also bind hemoglobin to form reversible cyanhemoglobin or bind hydroxocobalamin to form nontoxic cyanocobalamin. Effective detoxification depends on adequate sulfur availability, particularly thiosulfate.
Causes And Sources
Cyanide exposure most commonly occurs during fires as a combustion by-product of natural and synthetic materials. Industrial sources include metal plating, microchip and plastic manufacturing, chemical synthesis, pesticides, and solvents such as artificial nail remover and metal polishes. Cyanide may also be produced during nitroprusside metabolism and by certain bacterial infections. Dietary sources include amygdalin-containing plants such as apricot pits, peach pits, apple seeds, pear seeds, and cassava. Jewelry making is another recognized exposure risk.
Clinical Features
The heart and brain are the most sensitive organs and are typically affected first. Neurologic manifestations include headache, confusion, syncope, seizures, and coma. Cardiovascular findings include dyspnea, chest pain, rapid progression to cardiorespiratory collapse, and death. Gastrointestinal symptoms such as nausea and vomiting may occur. Oral exposure can be caustic, with as little as 50 mg causing death. Inhalational exposure to 50 ppm may cause anxiety, palpitations, dyspnea, and headache, while concentrations of 100–135 ppm can be lethal in less than one hour.
Initial Evaluation
A history suggestive of smoke inhalation, industrial exposure, or intentional ingestion should raise suspicion. Classic findings such as the odor of bitter almonds or bright red retinal vessels are often absent. Key clinical clues include abrupt onset or rapid deterioration, severe lactic acidosis, and elevated venous oxygen saturation due to impaired cellular oxygen utilization, resulting in arterialized venous blood gases.
Diagnostic Studies
Laboratory evaluation typically includes complete blood count, metabolic panel, liver profile, creatine phosphokinase, carboxyhemoglobin, and methemoglobin levels. Cyanide levels are usually send-out tests and not available in real time; levels above 0.5–1 mg/L are toxic, and levels of 2.5–3 mg/L are often fatal. Blood gas analysis may show elevated mixed venous oxygen saturation, reduced arteriovenous oxygen difference, and markedly elevated lactate levels greater than 8 mmol/L, which serve as a useful surrogate marker when exposure history is consistent. Chest radiography may assist in evaluating concurrent inhalation injury.
Conditions To Differentiate
The differential diagnosis includes carbon monoxide poisoning, hydrogen sulfide exposure, methemoglobinemia, sulfhemoglobinemia, inert gas asphyxiation, and other causes of high anion gap metabolic acidosis.
Prehospital Management
Immediate removal from the source of exposure is critical, while preventing secondary contamination of rescuers. Contaminated clothing should be removed and bagged, and liquid exposures require thorough washing with soap and water. Vapor exposures may resolve with simple removal from the environment.
Emergency Stabilization
Initial management follows standard airway, breathing, and circulation principles. Administer 100% oxygen regardless of measured oxygen tension, as it acts synergistically with antidotes. Gastric lavage and activated charcoal may be considered for recent oral ingestion if no contraindications exist. Dermal exposures require standard decontamination measures.
Definitive Treatment
Hydroxocobalamin is the preferred first-line antidote for patients with significant toxicity, including persistent high anion gap metabolic acidosis, hyperlactatemia, seizures, syncope, dysrhythmias, or hypotension. It binds cyanide to form cyanocobalamin, which is renally excreted. Advantages include the absence of methemoglobinemia and hypotension. Limitations include cost, drug incompatibilities within IV lines, and interference with certain laboratory assays.
An alternative is the traditional cyanide antidote kit, which includes amyl nitrite, sodium nitrite, and sodium thiosulfate. Nitrites induce methemoglobinemia to sequester cyanide away from mitochondria, while sodium thiosulfate enhances enzymatic detoxification via rhodanese. Nitrites should not be used empirically and require caution due to the risk of excessive methemoglobinemia and hypotension. Hyperbaric oxygen therapy may be considered as adjunctive treatment to maximize tissue oxygenation.
Medication Summary
First-line therapy is hydroxocobalamin administered intravenously at weight-based dosing, with repeat dosing if necessary. Activated charcoal may be used for recent ingestions. Second-line therapy involves the cyanide antidote kit, including carefully dosed nitrites and sodium thiosulfate. Special dosing considerations apply in pediatric patients, pregnancy, and those with hepatic or renal impairment.
Disposition And Follow-Up
All symptomatic patients require intensive care unit admission. Asymptomatic patients may be discharged after at least four hours of observation if no symptoms develop, as survival beyond this period is usually associated with full recovery. Psychiatric evaluation is indicated for intentional exposures.
Key Clinical Insights And Common Errors
In patients presenting with hypotension, seizures, altered mental status, severe lactic acidosis, and high anion gap metabolic acidosis, cyanide poisoning should be strongly considered and treated empirically. Serum lactate is a valuable surrogate marker when exposure history is suggestive. Victims of smoke inhalation may have combined cyanide toxicity, carbon monoxide poisoning, and methemoglobinemia. When carbon monoxide levels are markedly elevated, concomitant cyanide exposure should be suspected. To avoid worsening oxygen delivery, initial treatment should prioritize hydroxocobalamin or sodium thiosulfate without nitrites when methemoglobinemia would be harmful.
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