Effect of caudal ketamine on minimum local anesthetic concentration of ropivacaine in children: a prospective randomized trial

Background Caudal ketamine has been shown to provide an effective and prolonged post-operative analgesia with few adverse effects. However, the effect of caudal ketamine on the minimum local anesthetic concentration (MLAC) of ropivacaine for intra-operative analgesia is unclear. Methods One hundred and sixty-nine children were randomized to five groups: Group C (caudal ropivacaine only), Group K-0.25 (caudal ropivacaine plus 0.25 mg/kg ketamine), Group K-0.5 (caudal ropivacaine plus 0.5 mg/kg ketamine), Group K-0.75 (caudal ropivacaine plus 0.75 mg/kg ketamine), and Group K-1.0 (caudal ropivacaine plus 1.0 mg/kg ketamine). The primary outcome was the MLAC values of ropivacaine with/without ketamine for caudal block. Results The MLAC values of ropivacaine were 0.128% (0.028%) in the control group, 0.112% (0.021%) in Group K-0.25, 0.112% (0.018%) in Group K-0.5, 0.110% (0.019%) in Group K-0.75, and 0.110% (0.020%) in Group K-1.0. There were no significant differences among the five groups for the MLAC values (p = 0.11). During the post-operative period the mean durations of analgesia were 270, 381, 430, 494, and 591 min in the control, K-0.25, K-0. 5, K-0.75, and K-1.0 groups respectively, which shown that control group is significantly different from all ketamine groups. Also there were significant differences between K-0.25 and K-0.75 groups, and between K-1.0 groups and the other ketamine groups. Conclusions Adding caudal ketamine to ropivacaine prolong the duration of post-operative analgesia; however, it does not decrease the MLAC of caudal ropivacaine for intra-operative analgesia in children.