An unusual explanation for low oxygen saturation.

Pulse oximeters are now commonplace in modern medical practice, but we still need to be aware of their limitations. We present here a case of a 62-yr-old gentleman who underwent general anaesthesia for a recurrent parietal meningioma. He had received multiple general anaesthetics in the past. Persistent low pulse oximetry readings in the perioperative period, without any suggestion of respiratory compromise, led us to investigate him further and to discover a new, but benign, haemoglobinopathy.