Cause:Cyanide

Pathophys:Cytochrome oxidase poisoning kills by cellular hypoxia, usually (diaphragmatic paralysis causes respiratory failure)

Ingestion, accidental or suicidal; may be absorbed through the skin. Inhalation in house fires is very common, from burning wood, wool, plastics, polyurethane, etc (Nejm 1991;325:1761); acetonitrile in nail glue remover; also in cyanogenic plants, eg, laetrile; nitroprusside metabolized to cyanide and builds up w high-dose infusions, renal failure or prolonged use

Sx:Nonspecific flushing, dizziness, headache intially, then agonal/stridorous breathing, coma, seizures

Si:Bitter almond smell to breath; retinal arteries and veins appear same color (elevated venous oxygen levels); tachycardia, later bradycardia; late cyanosis, poor respiratory effort, confusion/stupor, coma

Chronic exposure from smoking can cause vit B₁₂ deficiency, amblyopia, psychosis, thyromegaly, ataxia

Lab:Chem:Low HCO₃ and pH from lactic acidosis; also seen in carbon monoxide poisoning; lactate levels >10 mM/L. Blood cyanide levels >40 mM/L. Venous blood gas has abnormally high O₂ saturation and pO₂. Lee-Jones spot test on gastric aspirate.

Rx:Supportive care including oxygen, iv fluids, and pressors

Cyanide antidote kit contains:

• Hydroxocobalamin, which combines with CN^– (Nejm 1991;325:1761); adult dose 5 grams iv, which may be repeated × 1 for partial response and pediatric dose 70 mg/kg and 2.5 g for weight less than 30 kg.
• Amyl nitrite inhalation to enhance methemoglobinemia because the CN^– binds strongly to Fe⁺⁺⁺ of methemoglobin too; but may be dangerous if carbon monoxide poisoning concomitantly (J Pharm Exp Ther 1987;242:70) or hemoglobinopathy. Methylene blue is also in kit to reverse methemoglobinemia; shouldn't be used.
• Sodium nitrite (NaNO₂) 0.2 mL/kg of 3% solution iv to max of 10 mL
• Sodium thiosulfate (Na₂S₂O₃) to form SCN^– that can be excreted; 12.5 gm/ampule