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For further information, see CMDT Part 40-31: 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

  • Emergency and supportive measures

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

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

    • Activated charcoal

      • Due to low affinity for cyanide, the usual doses of 60–100 g are adequate to bind typically ingested lethal doses (100–200 mg)

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

  • In the United States, there are two antidote regimens (eTable 40–1)

    • Hydroxocobalamin

    • Nithiodote

  • Hydroxocobalamin

    • Preferred regimen; directly binds and detoxifies free cyanide

    • Adult dose: 5 g intravenously

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

  • Nithiodote

    • 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

eTable 40–1.Currently available cyanide (CN) antidote kits.

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