NADH-diaphorase deficiency identified in a patient with congenital methaemoglobinaemia detected by pulse oximetry.

We report on a young woman with congenital methaemoglobinaemia detected by a pulse oximeter during anaesthesia. Investigation of the patient and her family showed that the methaemoglobinaemia resulted from a recessive deficiency of NADH-diaphorase enzyme. A knowledge of the working principles and limitations of pulse oximetry is essential to determine appropriate management in desaturation episodes during the perioperative period.