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 S(+)-ketamine after caudal or intramuscular administration in children to distinguish between 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 (caudal 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 hemodynamic and respiratory monitoring for 6 h in the recovery room. Analgesic requirements in the recovery room were assessed by an independent blinded observer using an observational pain/discomfort scale (OPS). Plasma samples for determination of ketamine concentrations were obtained before and 10, 20, 30, 45, 60, 90, 120, and 180 min after injection of S(+)-ketamine.

Results: A significantly longer duration of analgesia (P < 0.001) was observed after caudal administration (528 min [220-1,440 min]; median [range]) when compared with intramuscular administration (108 min [62-1,440 min]) of S(+)-ketamine. Plasma levels of ketamine were significantly lower from 10 to 45 min after caudal administration than after intramuscular injection.

Conclusion: Caudal S(+)-ketamine provides good intra- and postoperative analgesia in children. Despite similar plasma concentrations during most of the postoperative observation period, caudal S(+)-ketamine provided more effective analgesia than did intramuscular S(+)-ketamine, indicating a local analgesic effect.