Sulfhemoglobinemia presenting as pulse oximetry desaturation.

SULFHEMOGLOBIN is a rare cause of cyanosis that is usually drug induced. The effects of sulfhemoglobin on pulse oximetry have not been reported widely. We present the case of a 48-yr-old woman who was scheduled to undergo palliative surgery. Before anesthesia, she had an oxygen saturation, measured by pulse oximetry (SpO2), of 85%. This apparent desaturation subsequently was discovered to be the result of a blood sulfhemoglobin concentration of 28%. She had been prescribed metoclopramide daily for more than 1 yr. Long-term ingestion of metoclopramide is a cause of drug-induced sulfhemoglobinemia.