Prolonged apnea after small single dose of intravenous tramadol.

We report an unusual case of respiratory depression and prolonged apnea after a single, 50-mg intravenous dose of tramadol. Shortly after an uneventful surgery and anesthesia, the patient was administered intravenous tramadol. Soon after the tramadol injection, the patient became apneic, did not respond to verbal command, and started exhibiting oxygen desaturation. He was quickly administered 100% oxygen and positive pressure ventilation via a Bain circuit, and it took 45 minutes for the spontaneous respiration to return to regular. The respiratory depression could be due to increased amount of (+)enantiomer in that ampoule of tramadol. Physiological parameters affecting the metabolism of either enantiomer of tramadol or perioperative drugs need to be evaluated, as do physiological changes affecting the activity or metabolism of (+enantiomer. This case report demonstrates that even a small single dose of tramadol administered intravenously in the immediate postoperative period after general anesthesia may manifest as sudden and prolonged apnea.