Cyanide poisoning

Learning objectives

Cyanide can be a colorless gas, such as hydrogen cyanide (HCN) or cyanogen chloride (CNCl), or a crystal form such as sodium cyanide (NaCN) or potassium cyanide (KCN)
Hydrogen cyanide is described as having a “bitter almond” odor, which is discernible by approximately 60% of the population
Cyanide poisoning may result from structural fires, smoke inhalation, industrial exposures, medical exposures such as sodium nitroprusside, and certain foods (lima beans and almonds)
Cyanide inhibits oxidative phosphorylation by binding to the enzyme cytochrome C oxidase and blocks the mitochondrial transport chain
The result is cellular hypoxia and the depletion of ATP leading to metabolic acidosis
Signs and symptoms begin at blood cyanide concentrations of approximately 40 mol/L
The average lethal dose of hydrogen cyanide taken by mouth is between 60 and 90 mg (adult)

Acute inhalation or ingestion

Early symptoms	Headache Dizziness Confusion Mydriasis Nausea and vomiting Weakness Tachypnea Tachycardia
Late symptoms	Apnea Hypotension Arrhythmia Myocardial ischemia Seizures Loss of consciousness Bradycardia
Severe exposure	Progressive features will result from end-organ damage secondary to anaerobic respiration and histotoxic hypoxia Hypotension Bradycardia Reduced Glasgow Coma Scale Respiratory depression Cardiovascular collapse Hyperlactatemia The patient may appear ‘pink’ due to high SvO2 following oxygen administration The smell of bitter almonds may be present