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Emergency Medical Minute


Apr 27, 2018

Author: Nick Hatch, M.D.

Educational Pearls:


  • Methemoglobinemia is when the iron in hemoglobin is in the Fe3+ (ferric) state rather than the normal Fe2+  (ferrous) state. Methemoglobin cannot release oxygen at the tissues.
  • Symptoms include cyanosis, headache, tachycardia, dyspnea, and lethargy.
  • Suspect in setting of hypoxia that does not improve with oxygenation, and clinical cyanosis with a normal PaO2 on ABG.
  • Treatment is methylene blue which reduces the iron back to the ferrous state.
  • Causes can be Dapsone, Lidocaine, Benzocaine.



Agarwal N, Nagel RL, Prchal JT. Dyshemoglobinemias. In: Disorders of Hemoglobin: Genetics, Pathophysiology, and Clinical Management, 2nd ed, Steinberg M (Ed), 2009. P.607

Cortazzo JA, Lichtman AD. (2014). Methemoglobinemia: a review and recommendations for management. Journal of Cardiothoracic and Vascular Anesthesia. 28:1043.

Darling R, Roughton F. (1942). The effect of methemoglobin on the equilibrium between oxygen and hemoglobin. American Journal of Physiology. 137:56.