Methemoglobinemia is a rare, potentially life-threatening disorder caused by oxidation of hemoglobin iron from the ferric (Fe3+) to the ferrous (Fe2+) state, impairing oxygen delivery to tissues. Although most cases of methemoglobinemia that are documented are reported after procedural use of benzocaine sprays, those occurring from over-the-counter benzocaine gel are uncommon and often underrecognized. We report a case of an elderly woman with multiple comorbidities who developed significant methemoglobinemia after prolonged Benzocaine use for oral discomfort. She presented with refractory hypoxemia unresponsive to escalating supplemental oxygen. Arterial blood gas analysis revealed elevated methemoglobin levels. Timely recognition and administration of methylene blue resulted in rapid resolution of symptoms. This case highlights the importance of considering methemoglobinemia in patients presenting with unexplained refractory hypoxia, especially in patients who report the use of local anesthetics.
Panossian et al. (Mon,) studied this question.