Methemoglobinemia: a systematic review of the pathophysiology, detection, and treatment.

Methemoglobin is the oxidized form of hemoglobin which does not bind to oxygen efficiently. An increased level of methemoglobin can be attributed to congenital enzymatic defects, alterations in the hemoglobin molecule, or as a result of medications and toxins. The main clinical characteristic of the disease include cyanosis which is unresponsive to oxygen therapy and blood that is chocolate color when drawn. Co-oximetry is the gold standard for diagnosis but arterial blood gas paired with pulse oximetry and serum methemoglobin levels can confirm the diagnosis clinically. Treatment is aimed at removal of the offending agent, if medication induced, and is directed at aggressive oxygen therapy and treatment with the antidote, methylene blue.