Analgesic effects of caudal and intramuscular S(+)-ketamine in children

Background: Previous studies suggest that caudal administration of ketamine cause effective analgesia. The purpose of the current study was to compare the clinical effectiveness and plasma concentrations of SC(+)-ketamine aft er caudal or intramuscular administration in children to distinguish betwee n local and systemic analgesia. Methods: After induction of general anesthesia, 42 patients, aged 1 to 7 yr , scheduled to undergo inguinal hernia repair randomly received a caudal (c audal group) or intramuscular (intramuscular group) injection of 1 mg/kg S( +)-ketamine. Intraoperatively, heart rate (HR), mean arterial pressure (MAP ) and arterial oxygen saturation were measured. Postoperative measurements included duration of analgesia, a four-point sedation score, and hemodynami c and respiratory monitoring for 6 h in the recovery room. Analgesic requir ements in the recovery room were assessed by an independent blinded observe r using an observational pain/discomfort scale (OPS), Plasma samples for de termination of ketamine concentrations were obtained before and 10, 20, 30, 45, 60, 90, 120, and 180 min after infection of S(+)-ketamine. Results: A significantly longer duration of analgesia (P < 0.001) was obser ved after caudal administration (528 min [220-1,440 min]; median [range]) w hen compared with intramuscular administration (108 min [62-1,440 min]) of S(+)-ketamine. Plasma levels of ketamine were significantly lower from 10 t o 45 min after caudal administration than after intramuscular injection, Conclusion: Caudal S(+)-ketamine provides good intra- and postoperative ana lgesia in children. Despite similar plasma concentrations during most of th e postoperative observation period, caudal S(+)-ketamine provided more effe ctive analgesia than did intramuscular S(+)-ketamine, indicating a local an algesic effect.