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 | *Suspect in any patient with cyanosis not responsive to supplemental O2 | ||
* | *Caused by exposure to oxidizing agent | ||
**Benzocaine | |||
**Dapsone | |||
**CN kit | |||
**Antimalarials | |||
==Clinical Features== | ==Clinical Features== | ||
* | *Depends on level of metHb | ||
**Pts with anemia or preexisting cardiopulmonary disease will show symptoms sooner | **''Pts with anemia or preexisting cardiopulmonary disease will show symptoms sooner'' | ||
**<20%: asymptomatic, gray-blue cyanosis | **<20%: asymptomatic, gray-blue cyanosis | ||
**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%: usually | **>70%: usually fatal | ||
==Differential Diagnosis== | ==Differential Diagnosis== | ||
==Diagnosis== | ==Diagnosis== | ||
*Co-oximetry | *Co-oximetry | ||
*SpO2 will initially be falsely elevated | **Measures relative levels of oxyhemoglobin, carboxyhemoglobin, methemoglobin, reduced hemoglobin | ||
**Usually performed on arterial blood sample, but fingertip CO-oximeter devices are available | |||
*SpO2 will initially be falsely elevated | |||
**Once MetHb >30% → SpO2 will fall to 80-85% | |||
*"Chocolate brown" color of blood | *"Chocolate brown" color of blood | ||
== | ==Management== | ||
*Methylene Blue | *Methylene Blue | ||
** | **Treat if symptomatic '''OR''' asymptomatic w/ MetHb >25% | ||
**1-2mg/kg Methylene Blue IV over 5min; repeat dose if | **1-2mg/kg Methylene Blue IV over 5min; repeat dose if no effect | ||
**Improvement seen | **Improvement seen within 20min | ||
==See Also== | ==See Also== | ||
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==References== | ==References== | ||
<references/> | |||
[[Category:Tox]] | [[Category:Tox]] | ||
Revision as of 22:40, 23 September 2015
Background
- Methemoglobin refers to ferric form of Hb (Fe3+) that is unable to bind O2
- Suspect in any patient with cyanosis not responsive to supplemental O2
- Caused by exposure to oxidizing agent
- Benzocaine
- Dapsone
- CN kit
- Antimalarials
Clinical Features
- Depends on level of metHb
- 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 fatal
Differential Diagnosis
Diagnosis
- Co-oximetry
- Measures relative levels of oxyhemoglobin, carboxyhemoglobin, methemoglobin, reduced hemoglobin
- Usually performed on arterial blood sample, but fingertip CO-oximeter devices are available
- SpO2 will initially be falsely elevated
- Once MetHb >30% → SpO2 will fall to 80-85%
- "Chocolate brown" color of blood
Management
- Methylene Blue
- Treat if symptomatic OR asymptomatic w/ MetHb >25%
- 1-2mg/kg Methylene Blue IV over 5min; repeat dose if no effect
- Improvement seen within 20min