Methemoglobinemia

Abstract

Methemoglobinemia is a rare cause of cyanosis in both adults and children. It arises from the production of dysfunctional hemoglobin containing oxidized Fe (3+) which results in reduced oxygen supply to the tissues. The causes of methemoglobinemia may be categorized as either hereditary or acquired. Acquired methemoglobinemia is the most common form and is often due to drugs or toxins which oxidize ferrous iron. Hereditary forms are due to Hemoglobin M or NADH reductase deficiency. Clinical symptoms depend upon methemoglobin levels and the presence of methemoglobin should be suspected if oxygen saturation, as measured by pulse oximetry, is significantly less than the oxygen saturation calculated from arterial blood gas analysis. The definitive diagnostic test for methemoglobinemia is multiple-wavelength co-oximetry. Treatment is aimed at removal of the agent responsible for the disorder, supplemental oxygen therapy and in severe cases administration of antidote, methylene blue.