Epidural clonidine for postoperative pain after lower abdominal surgery: A dose - response study

Background: Patient controlled epidural analgesia with local anesthetic and opioid is an effective technique for postoperative analgesia after abdominal surgery. Clonidine has a synergistic effect on epidural local anesthetics. The purpose of this study was to determine the optimal epidural clonidine dose to be added to a solution of bupivacaine and morphine for patient controlled epidural analgesia to deliver an optimal balance of analgesia and side effects. Methods: Sixty patients were randomly assigned to three study groups (C0, C1, C2) of 20 patients each. Before the induction of general anesthesia, epidural anesthesia was induced using 10 mL of 1% lidocaine and epinephrine (1:200,000) and was maintained with a continuous infusion of the lidocaine - epinephrine solution until the completion of surgery. After surgery, groups CO, C1, and C2 received patient controlled epidural analgesia (PCEA) with morphine (0.1 mg/mL) in 0.1% bupivacaine. Group C1 and C2 also received epidural clonidine (1 and 2 mcg/mL, respectively). Pain was assessed at rest, cough, and on movement at 1, 2, 4, 8, 12 h after surgery and on day 1, 2, and 3. Differences in the mean postoperative Numerical Rating Scale (NRS) score and analgesic consumption were assessed by one-way analysis of variance and multiple comparisons. Result: Patients in all the groups experienced adequate pain relief during the 72-h period after surgery. There was no statistically significant difference between the mean NRS scores and CRS scores for pain at rest, cough, or during mobilization between the three groups. The cumulative volumes of analgesic solution were C0, 131 ± 21.285 mL; C1, 89.9 ± 18.44 mL; and C2, 80.1 ± 21.32 mL. There was no significant difference in the PCEA analgesic consumption between group C1 and C2 (P = 0.128). Groups C1 and C2 required lower volume of analgesic solution (P < 0.001) than group C0. Also, the number of rescue doses consumed by clonidine group were less (P < 0.001). Conclusion: The optimal epidural clonidine concentration in a morphine (0.1 mg/mL) and bupivacaine (0.1%) solution after lower abdominal surgery is 1.0 μg/ml. The combination of bupivacaine (0.1 %), morphine (0.1%), and clonidine (both 1 and 2 μg/mL) resulted in excellent pain relief in the 72 hour period after surgery and was not accompanied by significant hypotension, sedation, sensory blockade, or motor blockade