Cyanide Poisoning

Key Features

• Cyanide is rapidly absorbed by inhalation, skin absorption, ingestion

• In gaseous form, hydrogen cyanide is an important component of fire smoke

• Cyanide-generating glycosides also found in the pits of apricots and other related plants

• Cyanide is generated by breakdown of nitroprusside; poisoning can result from rapid high-dose infusions

• Also formed by metabolism of acetonitrile, found in some over-the-counter fingernail glue removers

Clinical Findings

• Onset of toxicity is nearly instantaneous after inhalation

• However, it may be delayed for minutes to hours after ingestion of cyanide salts or cyanogenic plants or chemicals

• Effects include

  • Headache

  • Dizziness

  • Nausea

  • Abdominal pain

  • Anxiety

  • Confusion

  • Syncope

  • Shock

  • Seizures

  • Coma

  • Death

• "Bitter almond" odor may be detected on the victim's breath or in vomitus, although this is not a reliable finding

Diagnosis

• The venous oxygen saturation may be elevated (> 90%) in severe poisonings because tissues have failed to take up arterial oxygen

Treatment

• Remove the victim from exposure, taking care to avoid exposure to rescuers

• Activated charcoal

  • Administer 60–100 g mixed in aqueous slurry orally or via gastric tube

  • Do not use for comatose or convulsing patients unless they are endotracheally intubated

• Stop or slow the nitroprusside infusion rate for suspected cyanide toxicity

• In the United States, there are prepackaged cyanide antidotes (eTable 38–1)

• Nithiodote

  • Conventional cyanide antidote package

  • Contains

    • Sodium nitrite (to induce methemoglobinemia, which binds free cyanide)

    • Sodium thiosulfate (to promote conversion of cyanide to the less toxic thiocyanate)

  • Administer 3% sodium nitrite solution, 10 mL intravenously followed by 25% sodium thiosulfate solution, 50 mL intravenously (12.5 g)

  • Caution: Nitrites may induce hypotension and dangerous levels of methemoglobin

• Hydroxocobalamin

  • A newer and potentially safer antidote

  • Adult dose: 5 g intravenously (children's dose is 70 mg/kg)

  • Note: Hydroxocobalamin causes red discoloration of skin and body fluids that may last several days and can interfere with some laboratory tests