Methemoglobinemia: Difference between revisions
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==Background== | ==Background== | ||
*Methemoglobin refers to ferric form of Hb (Fe3+) that is unable to bind O2 | *Methemoglobin refers to ferric form of Hb (Fe3+) that is unable to bind O2 | ||
*Caused by exposure to oxidizing agent (benzocaine, CN kit,antimalarials) | *Caused by exposure to oxidizing agent (benzocaine, CN kit, antimalarials) | ||
*Suspect in any pt whose cyanosis does not respond to supplemental O2 | *Suspect in any pt whose cyanosis does not respond to supplemental O2 | ||
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**20-30%: anxiety, HA, weakness, light-headedness, tachycardia | **20-30%: anxiety, HA, weakness, light-headedness, tachycardia | ||
**50-60%: myocardial ischemia, dysrhythmias, depressed mental status, seizure | **50-60%: myocardial ischemia, dysrhythmias, depressed mental status, seizure | ||
**>70%: | **>70%: usually lethal | ||
==Diagnosis== | ==Diagnosis== | ||
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*Methylene Blue | *Methylene Blue | ||
**Reserved for symptomatic pts or asymptomatic pts w/ MetHb >25% | **Reserved for symptomatic pts or asymptomatic pts w/ MetHb >25% | ||
**1-2mg/kg | **1-2mg/kg Methylene Blue IV over 5min; repeat dose if needed | ||
**Improvement seen w/in 20min | **Improvement seen w/in 20min | ||
Revision as of 00:22, 12 February 2013
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
Source
- Tintinalli