Activation of N-methyl-D-aspartic acid (NMDA) receptors leads to Ca++ entry into the cell and initiates a series of central sensitization such as wind up and longterm potentiation in the spinal cord. Therefore, it can be postulated that the central sensitization would be prevented by blocking Ca++ entry with verapamil. In this double-blind study, we administered lumbar epidural bupivacaine or bupivacaine plus verapamil to verify whether preoperative epidural anesthesia can preempt postoperative pain and to investigate the possible role of calcium channel blocker, verapamil, in the central sensitization.

Sixty patients (ASA class I-II) scheduled for lower abdominal surgery were randomly assigned to one of three groups of equal size. Group 1 (PR) is preincisional epidural bupivacaine group. Group 2 (PO) is postincisional epidural bupivacaine group. Group 3 (PRV) is preincisional epidural bupivacaine and verapamil group. Visual analogue pain and mood scores, Prince Henry Scores, sedation scores, cumulative PCA (patient controlled analgesia) morphine consumptions, and the incidence of side effects were assessed at 2, 6, 12, 24, 48 hours after operation.

Cumulative PCA morphine consumptions in PRV group was significantly lower than in PR and PO group at 24, 48 hours after surgery. The incidence of side effects had no difference among three groups.

Preoperative epidural anesthesia with 10ml of bupivacaine would be insufficient to preempt postoperative pain in lower abdominal surgery. However, addition of verapamil to preoperative epidural bupivacaine would decrease postoperative pain possibly by preventing the establishment of central sensitization.