To examine the influence of epidural morphine on the end-tidal sevoflurane concentration titrated to maintain bispectral index (BIS) values between 40 and 50.

Prospective, double-blinded clinical trial.

Anesthesia department of a university hospital.

40 ASA physical status I, II, and III patients scheduled for elective coloproctological surgery.

Patients were randomized to receive via a thoracic epidural catheter either a) bupivacaine 0.25% (10 mL) and saline 0.9% (2 mL) as a bolus followed by an infusion of bupivacaine 0.25% (5 mL/hr) or b) bupivacaine 0.25% (10 mL) and morphine 0.1% (2 mL) as a bolus followed by an infusion of bupivacaine 0.25% plus morphine 0.025% (5 mL/hr). Anesthesia was induced with propofol, fentanyl 2 μg kg^–1 and atracurium and maintained with sevoflurane and nitrous oxide in oxygen. Sevoflurane level was titrated to maintain a BIS value between 40 and 50. After extubation, patients were asked about the presence of pain.

There was no significant difference between groups of end-tidal sevoflurane concentrations at identical BIS values and hemodynamic values at any time in the study. However, the morphine group had a lower pain score level at extubation than did the plain bupivacaine group (no pain on movement, 79% vs. 31.5%, p < 0.01).

Adding morphine to the bupivacaine epidural solution did not reduce sevoflurane requirements but did provide high-quality postoperative analgesia, mainly just after tracheal extubation.