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Pathophys and Cause ⬇

Cause:Cyanide

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

Epidemiology ⬆ ⬇

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

Signs and Symptoms ⬆ ⬇

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

Complications ⬆ ⬇

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

Lab and Xray ⬆ ⬇

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.

Treatment ⬆

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