Background and Objectives. Although local anesthesia has been demonstrated to potentiate spinal morphine analgesia in animal studies, results comparing epidural local anesthesia/opioid mixtures with opioid alone are contradictory in clinical studies. The hypothesis was that, although the concentration of bupivacaine (0.1%) was low to minimize its adverse effects, if the infusion rate of a fentanyl/bupivacaine solution was closely adjusted according to need, the presence bupivacaine would reduce the requirement for epidural fentanyl.

Methods. Forty patients were randomly assigned to receive either fentanyl (10 μg/mL) or a fentanyl/bupivacaine (0.1%) mixture epidurally corresponding to the dermatome of the surgical incision in a double-blind fashion for the first 18 hours after major abdominal surgery. The infusion was titrated for each patient to the rate required for pain relief during forced inspiration (pain score ≤2, maximum 10). Pain scores, the fentanyl doses required, plasma concentrations of fentanyl at 18 hours, and the incidence and severity of adverse effects were recorded.

Results. Patients reported similar median pain scores and were equally satisfied with pain relief in both groups. The mean required postoperative fentanyl infusion rate (57.7 ± 19.5 μg/h) and the plasma concentrations (0.84 ± 0.36 ng/mL) in the fentanyl group were comparable to the infusion rate (54.4 ± 19.2 μg/h) and the plasma concentrations (0.86 ± 0.36 ng/mL) in the fentanyl/bupivacaine group. Respiratory and cardiovascular functions were preserved, and the incidence of nausea, pruritus, and periods of drowsiness or sleep were similar in both groups.

Conclusions. In low concentrations (0.1%), bupivacaine did not reduce the titrated dose of epidural fentanyl required for adequate pain relief during forced inspiration after major abdominal surgery. The incidence and severity of adverse effects were also comparable whether or not low-dose bupivacaine infusion was used.