Background and Objectives: Ketamine administered systemically is a potent analgesic at subanesthetic plasma concentrations. Addition of ketamine to bupivacaine for caudal epidural block significantly prolongs the duration of postoperative analgesia. The purpose of this prospective, randomized double-blind study is to identify the optimal dose of ketamine that produces the maximum duration of caudal analgesia with minimal adverse effects as an adjuvant to bupivacaine for caudal epidural block.

Methods: Sixty children, aged 6 months to 10 years, undergoing inguinal herniotomy were allocated randomly to receive 1 of 3 solutions for caudal epidural block. Group 1 received 0.75 mL/kg of bupivacaine 0.25% with preservative-free ketamine 0.25 mg/kg, group 2 received 0.75 mL/kg of bupivacaine 0.25% with ketamine 0.5 mg/kg, and group 3 received 0.75 mL/kg of bupivacaine 0.25% with ketamine 1 mg/kg. Postoperative pain was assessed using the All India Institute of Medical Sciences pain discomfort scale. Rescue analgesia in the form of pethidine 1 mg/kg intramuscularly was administered when this score exceeded 4.

Results: The mean duration of caudal analgesia was 8.8 hours in group 1 compared with 22.1 hours in group 2 (P < .001) and 25.2 hours in group 3 (P < .001). Supplemental analgesia requirements with pethidine were significantly less in group 2 (4 subjects) and group 3 (no subject) when compared with group 1 (18 subjects). There were no differences between the groups in the incidence of motor blockade, urinary retention, emesis, or sedation. Group 3 had a significantly higher incidence of behavioral side effects such as odd behavior, agitation, or restlessness than groups 1 and 2.

Conclusions: The optimal dose of ketamine in our study was 0.5 mg/kg added to 0.75 mL/kg bupivacaine 0.25% for caudal epidural block without an increase in side effects.