Epidural bupivacaine for aortic surgery The effect of dilution on the quality of analgesia

Abstract

SummaryTwenty patients undergoing elective abdominal aortic aneurysm repair were randomly allocated to two groups and studied for 24 h following surgery. Postoperative analgesia was provided by epidural bupivacaine infusion and intravenous patient-controlled 0.05 mg boluses of alfentanil. One treatment group received 7 m1.h-l of a 0.25% solution of bupivacaine, the other 25 m1.h-' of a 0.07% solution. The rate of infusion was thus 17.5 mg.h-' in both groups. Patients receiving 7 m1.h-I of epidural infusate required more doses of alfentanil (median 26.5, range 0-50) than the group receiving 25 m1.h-I of the dilute infusion (median 3.0, range 0-16). It is concluded that 17.5 mg.h-' of bupivacaine infused into the epidural space produces better analgesia when infused in a volume of 25 m1.h-I (0.07%) than when given in a volume of 7 ml.h-' of solution (O.tS%). Key wordsAnaesthetic techniques, regional; epidural. Analgesics; alfentanil. Surgery; cardiovascular.Injection of local anaesthetic into the epidural space is an established technique for providing postoperative analgesia. To minimise the risk of total spinal anaesthesia as a result of catheter migration [I], and the hypotension caused by sudden reduction in sympathetic tone, a continuous infusion of local anaesthetic solution can be used. The analgesia produced by such regimens is, however, often disappointing [2]. Most work on epidural infusions of local anaesthetic without added opioid has been done on parturient women, in whom it has been found that the quality of analgesia can be improved greatly by diluting the local anaesthetic and infusing a higher volume [3,4]. The purpose of this study was to determine whether this is also true in elderly high-risk patients undergoing aortic surgery. In these patients, who are most often over 60 years old, coexistent disease is almost invariable [5]. MethodApproval was obtained for the study from the local ethics committee, and informed written consent was obtained from all patients. The entire study was carried out over a period of 8 months at the Royal Bournemouth General Hospital. Thirty-five ASA 1-3 patients, aged 18-75 years, weighing c 90 kg who were scheduled for repair of an abdominal aortic aneurysm and who were suitable for epidural analgesia were studied. Patients were not studied if surgical considerations necessitated other than a transverse incision, if epidural block could not be demonstrated on recovery from anaesthesia, if the patient was unable to make appropriate use of a patient-controlled analgesia (PCA) device, or if, despite an effective epidural block and use of the PCA device, the patient was felt to have inadequate pain control. This was defined as an analogue pain score of 3 or above on a scale of 1-5 at the end of an hour in which six or more boluses of alfentanil had been administered. On entering the study, patients were randomly allocated to one or other of the treatment groups according to a block randomisation sequence (with four patients per block), generated by computer before comme...