Intrathecal morphine during thoracotomy, Part I: Effect on intraoperative enflurane requirements

The ability of intrathecal morphine to reduce the anesthetic requirements during thoracotomy was investigated. Twenty-four patients scheduled for thoracic surgery were studied. Anesthesia was induced with thiamylal sodium, 4 mg/kg, fentanyl, 100 micrograms, and 100 mg of succinylcholine. Prior to skin incision, 12 patients received intrathecal injection of 12 micrograms/kg of preservative-free morphine sulfate (ITM), while the remaining 12 patients served as controls. The ITM was given undiluted at the L3-4 or L4-5 level. Anesthesia was maintained solely with enflurane, titrated to keep mean arterial pressure within 15% of the preoperative values. Vecuronium was given as required for relaxation. No additional narcotics were administered. Throughout the procedure, end-tidal (ET) enflurane concentration was recorded at 15-minute intervals from the mass spectrometer (Perkin Elmer). The intraoperative mean ET concentration of enflurane was significantly reduced in the ITM group beginning 1 hour after the injection (1.19 +/- .45% in the control group versus 0.73 +/- 0.08% in the ITM group). The enflurane requirements, expressed as percent end-tidal enflurane/hour, were significantly less in the ITM group for the duration of the procedure (0.8 +/- .17 v 1.08 +/- .22, respectively). In conclusion, when administered prior to skin incision for post-thoracotomy pain control, intrathecal morphine reduces intraoperative enflurane requirements.