Methemoglobinemia

Revision as of 00:22, 12 February 2013 by Matthew. Lipton (talk | contribs)

Background

  • Methemoglobin refers to ferric form of Hb (Fe3+) that is unable to bind O2
  • Caused by exposure to oxidizing agent (benzocaine, CN kit, antimalarials)
  • Suspect in any pt whose cyanosis does not respond to supplemental O2

Clinical Features

  • Levels
    • Pts with anemia or preexisting cardiopulmonary disease will show symptoms sooner
    • <20%: asymptomatic, gray-blue cyanosis
    • 20-30%: anxiety, HA, weakness, light-headedness, tachycardia
    • 50-60%: myocardial ischemia, dysrhythmias, depressed mental status, seizure
    • >70%: usually lethal

Diagnosis

  • Co-oximetry
  • SpO2 will initially be falsely elevated until MetHb >30% (SpO2 will then fall to 80-85%)
  • "Chocolate brown" color of blood

Treatment

  • Methylene Blue
    • Reserved for symptomatic pts or asymptomatic pts w/ MetHb >25%
    • 1-2mg/kg Methylene Blue IV over 5min; repeat dose if needed
    • Improvement seen w/in 20min

See Also

Toxidromes

Source

  • Tintinalli
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