IBCC EP 60 - Methemoglobinemia

Methemoglobinemia occurs when hemoglobin is oxidized from its reduced Fe2+ state to a ferric Fe3+ state, rendering it incapable of transporting oxygen or carbon dioxide. Common triggers include local anesthetics like benzocaine, nitrates, certain antibiotics such as dapsone, and illicit substances like amyl nitrate. Clinical diagnosis relies on identifying the "saturation gap"—where pulse oximetry remains stuck around 85% despite high supplemental oxygen—and observing characteristic chocolate-colored blood. While methylene blue serves as the primary treatment for symptomatic cases, clinicians must exercise caution due to potential side effects and the risk of hemolysis in patients with G6PD deficiency. In refractory or complex cases, alternative therapies like vitamin C, riboflavin, or exchange transfusions may be necessary. Recognizing these clinical clues is essential for timely intervention, as severe cases can lead to seizures, coma, or death.