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Double-blind randomized controlled trial of caudal versus intravenous S(+)-ketamine for supplementation of caudal analgesia in children.

BACKGROUND
The postoperative analgesic efficacy of S(+)-ketamine after caudal or i.v. administration following sub-umbilical surgery in children was studied to investigate its principal site of analgesic action.


METHODS
Sixty children undergoing caudal block during general anaesthesia for hernia repair or orchidopexy were prospectively randomized to one of three groups: the bupivicaine group received plain bupivacaine 0.25% 1 ml x kg(-1); the caudal ketamine group received caudal plain bupivacaine 0.25% 1 ml x kg(-1) with S(+)-ketamine 0.5 mg x kg(-1); the i.v. ketamine group received caudal plain bupivacaine 0.25% 1 ml x kg(-1) plus S(+)-ketamine 0.5 mg x kg(-1) i.v. Postoperative measurements included analgesic requirements and modified objective pain score for the first 24 h.


RESULTS
The median time to first analgesia was significantly longer in the caudal ketamine group (10 h) than in the i.v. ketamine (4.63 h) or bupivacaine (4.75 h) groups (P=0.01). Significantly fewer doses of analgesia were required over the first postoperative 24 h by subjects in the caudal ketamine group (median 1) compared with the i.v. ketamine (median 2) or bupivacaine (median 2.5) groups (P<0.05). There was no difference between the groups in the incidence of postoperative nausea and vomiting or psychomotor reactions.


CONCLUSIONS
We have demonstrated that the addition of caudal S(+)-ketamine to bupivacaine prolongs the duration of postoperative analgesia. However, the same dose of i.v. S(+)-ketamine combined with a plain bupivacaine caudal provides no better analgesia than caudal bupivacaine alone, indicating that the principal analgesic effect of caudal S(+)-ketamine results from a local neuroaxial rather than a systemic effect.