Makindo Medical Notes

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In cases of lethal cyanide overdose, death typically occurs pre-hospital. However, survival to hospital usually has a favorable prognosis. Cyanide is a colourless liquid or gas with a characteristic almond-like odor.

About

• Highly toxic: Cyanide is a highly toxic and potentially fatal substance, often resulting in pre-hospital mortality due to its rapid action on the body.
• Common Exposure Sources: Consider cyanide toxicity especially in cases of exposure from domestic fires, where smoke inhalation can lead to significant risk.
• Historical Context: Historically, cyanide has been used in genocide gas chambers during World War II, highlighting its lethal potential.

Chemistry

• Isolation History: Hydrogen cyanide was first isolated from Prussian blue dye in 1786, and cyanide was extracted from almonds around 1800, linking the compound to natural sources.
• Forms: Cyanide exists as a gas (hydrogen cyanide) or as a salt (e.g., potassium cyanide), both of which are highly toxic.

Epidemiology

• Accidental Exposure: Cyanide exposure can occur accidentally, particularly in the chemical industry or from industrial accidents.
• Intentional Ingestion: May also occur due to deliberate suicide or homicide attempts, reflecting the compound's accessibility and toxicity.
• Fire-Related Incidents: Commonly associated with enclosed fires involving plastics or foam, leading to toxic smoke inhalation.
• Drug Interactions: High-dose or prolonged use of sodium nitroprusside, a medication used for hypertensive emergencies, can result in cyanide toxicity.

Aetiology

• Cyanide causes cellular asphyxiation by inhibiting cellular respiration.
• Inhalation of hydrogen cyanide gas inhibits cytochrome a3, blocking mitochondrial oxidative phosphorylation and significantly reducing ATP production, leading to cellular failure.

Clinical Features

• Mild to Moderate Symptoms: Symptoms may include dizziness, anxiety, tachycardia, nausea, drowsiness, eye irritation, and skin flushing.
• Characteristic Findings: Clinicians may observe soot in the mouth, a cherry-red skin colour due to reduced oxygen extraction, and the distinctive smell of bitter almonds on the breath.
• Severe Symptoms: These can progress to vomiting, low GCS, convulsions, cyanosis, chest pain, dyspnea, seizures, deep coma, fixed pupils, heart failure, arrhythmias, and pulmonary edema.
• Neurological Impairment: Severe cyanide toxicity can lead to rapid deterioration in neurological status, necessitating urgent intervention.

Investigations

• ABG: Arterial blood gas analysis typically shows metabolic acidosis with elevated lactate levels, indicating anaerobic respiration.
• Lactate Levels: Elevated lactate levels suggest significant cyanide overdose and help assess the severity of the condition.
• Serum Cyanide Levels: In some cases, measuring serum cyanide levels can assist in confirming diagnosis, though treatment should not be delayed for this test.

Management

• Immediate Actions: Administer high-flow 100% oxygen, decontaminate if applicable, and initiate IV fluids for supportive care, especially in mild cases.
• Specific Treatments: There are several specific treatments available for cyanide toxicity:
• Dicobalt Edetate: Administer 300 mg IV over 1 minute followed by 50 ml of 50% dextrose; reserved for severe toxicity due to its own toxicity profile.
• Hydroxycobalamin (Cyanokit): Administer 5 g IV over 15 minutes; it binds cyanide to form cyanocobalamin, a non-toxic compound that is excreted by the kidneys.
• Sodium Thiosulfate: Administer 25 ml of 50% solution; enhances the conversion of cyanide to thiocyanate, which is renally excreted.
• Given the potential fatality, expert consultation with a poison control center is strongly recommended for managing severe cases.
• Continuous Monitoring: Continuous cardiac monitoring is essential, as arrhythmias can develop rapidly in cases of severe toxicity.

References

• Cyanide Toxicity: Clinical Management
• Cyanide Basics and Facts