Methaemoglobinaemia in the newborn infant.

Methaemoglobinaemia is a rare condition in which the haemoglobin iron is in the oxidized or ferric state and cannot reversibly bind oxygen. If severe, this condition leads to hypoxaemia and death. Methaemoglobinaemia may be acquired by exposure to oxidant drugs or chemicals. Alternatively, it may be inherited due either to a haemoglobinopathy, which renders the haem iron more susceptible to oxidation, or to a defect in the erythrocyte's enzymatic capacity to return methaemoglobin to the reduced state. Newborn infants have an increased risk of methaemoglobinaemia due to a normal transient deficiency of methaemoglobin reductase in neonatal erythrocytes and the increased tendency of fetal haemoglobin to assume the met-configuration. The clinical approach to the neonate with methaemoglobinaemia is no different from the approach to older patients. The need for therapy is dictated by the severity of hypoxic symptoms. Since the diagnosis is made simply and the treatment is effective, a high index of clinical suspicion may be potentially life-saving.