Epidemiology
Etiology
- Dapsone
- Local/topical anesthetics (eg, benzocaine, teething medications)
- Nitrates/nitrites (eg, drinking ground water)
Pathophysiology
- Methemoglobin is created when reduced ferrous iron (Fe2+) bound to oxyhemoglobin is oxidized to ferric iron (Fe3+).
- Ferric iron in methemoglobin cannot bind oxygen→ ↓ total blood oxygen content and ↓ blood oxygen saturation → tissue hypoxia
Tip
The ferric iron in methemoglobin has a high affinity for cyanide, thus, amyl nitrite-induced methemoglobin is used as a competitive inhibitor in the treatment of cyanide poisoning.
Clinical features
- Cyanosis (brownish-blue or gray skin and membranes)
Diagnostics
Treatment
- Methylene blue is the first-line treatment for acquired methemoglobinemia.
- Acts as a cofactor to reduce methemoglobin to hemoglobin
Tip
100% supplemental oxygen is not useful in methemoglobinemia, in contrast to monoxide poisoning and cyanide poisoning.