[Postoperative peridural analgesia via catheter following abdominal surgery. Peridural bupivacaine versus buprenorphine].

Seventy-five patients scheduled for major abdominal operations were randomly divided into four groups, each with a different postoperative analgesic regime. Group I: buprenorphine 4 micrograms/kg was injected i.v. every 4 h. Groups II-IV: all patients were preoperatively supplied with a thoracic epidural catheter that, however, was not used during the operation. Group II: bupivacaine 0.15 ml/kg was injected epidurally every 2 h, the first dose being 0.5%, the top-ups 0.25%. Group III: buprenorphine 4 micrograms/kg in 10 ml saline was given via the catheter and repeated on request. Group IV: these patients received a combined regime. Bupivacaine was injected as in group II, and in addition buprenorphine was added epidurally in the doses and time intervals of group I. After extubation the patients categorized the intensity of postoperative pain twice, first while lying immobile and then after coughing vigorously, using a rating scale with pain scores from 0 to 10. Thereafter, the analgesic regime described above commenced. One hour later the patients' pain scores were again determined. In addition to pain scores, heart rate (HR), mean arterial pressure (MAP) and paCO2 were recorded at the same points in time. The investigation was then interrupted overnight. The analgesic regime continued as described for groups I and II. Patients in group III received 0.15 mg buprenorphine on request i.v., and in group IV bupivacaine was given as in group II with no further buprenorphine. The study recommenced the next morning at 7:00 a.m. After the initial values (pain scores, HR, MAP, paCO2) had been recorded the analgesic program, as scheduled for each patient, restarted. In group IV buprenorphine was again added to bupivacaine and repeated every 4 h, whereas bupivacaine was injected every 2 h. All values were registered hourly until 7:00 p.m., when the investigation was terminated. RESULTS. On the day of operation and during the first few hours on the morning thereafter, analgesia in groups II and IV was considerably better compared to groups I and III (P less than 0.001). We could not statistically demonstrate, however, that analgesia in group IV was superior to that in group II despite the fact that pain scores were lowest in this group, with a median at rest of 0 throughout the study time. In group III (n = 20), epidural buprenorphine failed to produce any acceptable analgesic effect in 6 patients despite correct catheter position. For this reason they were dropped from the study. No patient in any of the other groups, however, was dropped (P less than 0.01). Later in the 1st postoperative day analgesia in groups II and IV lost its superiority at rest, but coughing continued to be less painful in comparison to groups I and III. We noticed that the duration of action of 0.25% bupivacaine, injected as a bolus, was considerably shorter than expected (less than 2 h) and that several patients experienced pain before the next top-up was given...