Cyanide Toxicity

Cyanides inhibit cellular respiration binding to the ferric ion of cytochrome oxidase, leading to histotoxic hypoxia and cellular asphyxia.

Cyanides are any chemical compound that contain the \(C \equiv N^-\) functional group; the most infamous being hydrogen cyanide (\(HC \equiv N\)) or prussic acid which has a bitter almond-odor and was the key component in Zyklon B.

Epidemiology and Risk Factors

Pathophysiology

Aetiology

Cyanide may be produced in:

  • Fires
    Classically burning plastics in an enclosed space.
  • Animal traps
  • Plants
    • Apricot pits
    • Bitter almonds
    • Peach stones
  • Industrial processes

Clinical Features

Features of Cyanide Toxicity
Moderate Severe
  • Brief syncope
  • Seizures
  • Dizziness
  • Restlessness
  • Vomiting
  • Stupor
  • Respiratory depression
  • Opisthotonus
  • Fixed, dilated pupils
  • ↑ CvO2
    ↓ Oxygen extraction ratio.
  • Hypotension
  • Lactic acidosis
  • Pulmonary oedema

Diagnostic Approach and DDx

Investigations

Bedside:

Laboratory:

Imaging:

Other:

Management

  • Remove cyanide through either:
    • Cyanide binding
    • Induced methaemoglobinaemia
      Binds free CN and forms cyanmethaemoglobin.
  • Supportive care

Resuscitation:

Specific therapy:

The pathology of methaemoglobinaemia is covered under Methaemoglobinaemia.

  • Pharmacological
    • Cyanide binders
      • Hydroxocobalamin 5g IV over 15 minutes
        Scavenges cyanide, which is then renally cleared.
        • Non-toxic
          Therefore, can be given empirically.
      • Dicobalt edetate 300mg IV over 1 minute followed by 50mL of 50% dextrose
        • Reserved for confirmed severe toxicity as it may cause seizures, airway oedema, and hypotension
      • Sodium thiosulphate 12.5g over 10 minutes
        Converts cyanide to thiocyante, which is renally cleared.
    • Induce methaemoglobinaemia
      • Sodium nitrate or amyl nitrate
        Produces methaemoglobin, and subsequently cyanomethaemoglobin.
      • Methylene blue
  • Procedural
  • Physical

Supportive care:

  • B
    • Supplemental oxygen
  • C
    • Vasoactive support
  • F
    • Correct acidosis
      • Bicarbonate
      • Consider RRT

Disposition:

Preventative:

Marginal and Ineffective Therapies

Anaesthetic Considerations

Complications

Prognosis

Key Studies

References

  1. Bersten, A. D., & Handy, J. M. (2018). Oh’s Intensive Care Manual. Elsevier Gezondheidszorg.
  2. Hall AH, Rumack BH. Clinical toxicology of cyanide. Ann Emerg Med. 1986;15(9):1067-1074. doi:10.1016/s0196-0644(86)80131-7