In Reply:-We thank Dr. Quist for his comments. However, the deliberate maintenance of high levels of epidural blockade with bupivacaine was not at all the aim of our study. Our aim was to use the potentially synergistic effect of bupivacaine and morphine to minimize the side effects (hemodynamic, motor blockade, pruritus) associated with either analgesic alone. In addition, as we pointed out in our article, epidural bupivacaine-morphine is known to provide superior analgesia on movement relative to epidural morphine alone after abdominal surgery. [1] Our use of 0.125% bupivacaine reflects our concerns about hemodynamic stability associated with higher concentrations; this is borne out by the experience of Liu et al., [2] who compared analgesia after colonic surgery using, among other modalities, epidural bupivacaine and epidural bupivacaine-morphine. These investigators reported an incidence of 57% and 36% for supine and absolute hypotension, respectively, during analgesia with 0.15% bupivacaine at a rate of 10 ml/h. During pilot data collection, we established that sensory levels using 0.125% bupivacaine could not be predictably elicited, and our protocol provided for deliberate decreases in infusion rate to a preset minimum of 4 ml/h, so as to minimize the chance of significant autonomic blockade. If we had elicited significant sensory blockade, it would have caused us concern.
To establish the relative contributions of bupivacaine and morphine to the analgesia obtained, we would have needed at least a third group that received epidural morphine only and maybe a fourth that received epidural bupivacaine only. For logistic reasons, this was impossible. However, the movement visual analog scale scores observed in our epidural group were very similar to those observed by Liu et al. [2] using a broadly similar bupivacaine-morphine regimen; these latter scores were superior to those during epidural morphine alone, and mobilization VAS scores were similar in patients who received either epidural morphine or patient-controlled intravenous morphine. These findings strongly suggest a contributory role for bupivacaine. It might have been interesting to examine this issue as part of our study, but we felt that the work of Liu et al. [2] had already answered this question definitively.
John F. Boylan, M.B., F.R.C.P.
Staff Anaesthetist; St. Vincent's University Hospital; Dublin 4, Ireland
Alan N. Sandler, M.B., F.R.C.P.
Anaesthetist-in-Chief; University Health Network and Mount Sinai Hospital; Professor of Anaesthesia; University of Toronto; Toronto, Canada M5G 2C4
(Accepted for publication February 1, 1999.)
