Abstract

Twenty-four otherwise healthy patients scheduled for elective major abdominal surgery received general anesthesia plus lumbar epidural analgesia with a loading dose of plain bupivacaine 0.5% to produce sensory analgesia (pinprick) from Th4 to S5. Two groups of patients were matched with regard to age, sex, height, body weight, and surgical procedure. The 12 patients in one group received continuous infusion of plain bupivacaine 0.5%, 8 ml/h, and the other group of 12 patients received plain bupivacaine 0.25%, 16 ml/h, starting 30 minutes after a loading dose of bupivacaine 0.5%, 23.0 ± 0.5 ml. Pain scores on a 5-point scale and sensory analgesia (pinprick) were assessed hourly for 16 hours after skin incision. If sensory analgesia decreased more than 5 segments from the preoperative level or if the pain score reached 2 (moderate pain), the patients were removed from the study, and pain was treated with opiates. Preoperative mean (±SEM) sensory levels of analgesia were similar in both groups (Th3.9 ± 0.7 and Th4.1 ± 0.5 ( p > 0.5). In the group receiving 8 ml/h of bupivacaine 0.5%, three patients maintained the initial level of sensory analgesia and pain score below 2 throughout the study period compared with three patients who received 16 ml/h of 0.25% bupivacaine. There was no significant difference in the duration of sensory analgesia (<5 segments regression) between the two treatments (9.5 ± 1.2 and 11.0 ± 1.0 hours [mean ± SEM] p > 0.3), respectively. Thus, the pronounced variation in interindividual regression of analgesia during continuous postoperative lumbar epidural infusion of 0.5% bupivacaine cannot be avoided by administration of a double volume of 0.25% bupivacaine.