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Reference 1. Badner NH, Reimer EJ, Komar WE, Moote CA. Low-dose bupivacaine does not improve postoperative epidural fentanyl analgesia in orthopedic patients. Anesth Analg 1991;72:33741.In Response:We thank Drs. Maves and Gebhart for their interest in our paper comparing the use of epidural fentanyl with epidural fentanyl and 0.1% bupivacaine (1). Our study was designed only to compare the concentrations used and not to determine if synergy does or does not occur between epidural opioids and local anesthetics. Our conclusions were therefore intended to convey the fact that the addition of 0.1% bupivacaine per se does not improve the efficacy of epidural fentanyl in a concentration of 10 pg/mL. We chose these concentrations as they are used routinely and have been reported by others to be superior to this concentration of epidural fentanyl alone ( 2 4 ) . We cannot argue with Drs. Maves and Gebhart's findings, as well as the findings of others (5), that the addition of local anesthetics to intruthecul opioids improves analgesia in rats. Our study simply showed that 0.1% bupivacaine is not the appropriate concentration for epidural fentanyl in a lO-pg/mL concentration in patients after total knee joint replacement. Although we suggested that morbidity was increased with the addition of 0.1% bupivacaine, the one case of respiratory depression was most likely due to the epidural fentanyl and not to an additive effect of the combination. In fact, as we suggested in the discussion, a higher concentration of bupivacaine may be necessary to allow a decrease in epidural fentanyl requirements and thereby show a synergistic effect. We are presently investigating this possibility in an ongoing study.

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