UMEM Educational Pearls

Category: Toxicology

Title: Methemoglobinemia

Keywords: Methemoglobinemia,methylene blue (PubMed Search)

Posted: 2/3/2011 by Ellen Lemkin, MD, PharmD (Updated: 9/28/2023)
Click here to contact Ellen Lemkin, MD, PharmD


Suspect methemoglobinemia if you have a patient with persistent cyanosis, tachypnea, low pulse oximetry, and a lack of response to 100% oxygen therapy, or an elevated PaO2 on ABG and a low O2 sat on pulse ox.
Methemoglobin results from exposure to chemicals that oxidize the ferrous iron in hemoglobin to the ferric state, resulting in a functional anemia.  Usually a low level is reduced back to hemoglobin by cytochrome b5, NAD, G6PD, and glutathione reduction enzyme systems.  
Diagnose by confirmed by a methemoglobin level, although the most convenient and rapid test of choice is multiple wave co-oximetry. (not the standard 2 wave pulse ox).
Treat if they are symptomatic; use methylene blue, 1 mg/kg slow push. Patients should improve in one hour. Use with extreme caution in patients with G6PD disease (if at all).