Methemoglobinemia: pathogenesis, diagnosis, and management.

The diagnosis of methemoglobinemia should be considered in patients presenting with cyanosis and hypoxia. A variety of frequently used medications are capable of inducing methemoglobinemia, with dapsone and benzocaine being common culprits. Unique features, such as a saturation gap and chocolate-brown-colored blood, can raise suspicion for methemoglobinemia. Typically, symptoms correlate with the methemoglobin level, and treatment with methylene blue is reserved for patients with significantly elevated methemoglobin levels. In the presence of comorbid conditions that impair oxygen transport, however, low-grade methemoglobinemia can become symptomatic and may warrant treatment.