Epidural fentanyl markedly improves thoracic epidural analgesia in a low-dose infusion of bupivacaine, adrenaline and fentanyl. A randomized, double-blind crossover study with and without fentanyl.

BACKGROUND: The objectives of the present study were to evaluate the effects on postoperative pain intensity, pain relief, and side effects when removing fentanyl from an optimally titrated epidural infusion consisting of bupivacaine, fentanyl and adrenaline.

METHODS: A prospective, randomized, double-blind, crossover study was carried out in 20 patients after major upper abdominal surgery requiring a large longitudinal incision. Patients with only mild pain when coughing during thoracic epidural infusion of about 10 ml per hour of bupivacaine 1 mg x ml(-1), fentanyl 2 microg x ml(-1), and adrenaline 2 microg x ml(-1) were included. On the 1st and 2nd postoperative days, each patient was given a double-blind epidural infusion, at the same rate, with or without fentanyl. The effects were observed for 6 h or until pain when coughing became unacceptable in spite of rescue analgesia. Rescue analgesia consisted of up to two patient-controlled epidural bolus injections (4 ml) per hour and intravenous morphine if necessary.

RESULTS: Main outcome measures, i.e. pain intensity when coughing and at rest, increased (P<0.001) when fentanyl (19.2+/-5.2 microg x h(-1)) was omitted from the epidural infusion: after 6 h pain intensity when coughing had increased to unacceptable levels in spite of increased consumption of rescue bupivacaine and adrenaline (P<0.001). Within 15-20 min after restarting the triple epidural mixture with fentanyl, pain intensity was again reduced to mild pain when coughing.

CONCLUSIONS: A low dose of epidural fentanyl (20 microg x h(-1)) markedly improved the pain-relieving effect of bupivacaine and adrenaline infused epidurally at a thoracic level after major upper abdominal surgery. This dose of fentanyl is much too small to relieve severe dynamic pain when given systemically. Therefore, this study indirectly supports the view that a low-dose thoracic epidural infusion of fentanyl has a spinal analgesic site of action.