Abstract
We wished to determine if the addition of a small dose of morphine (0.05 mg.kg−1) to a caudal solution of 0.25% bupivacaine could extend the duration of analgesia after major reconstructive penile surgery and also to measure the systemic absorption of morphine after caudal injection. Thirty children undergoing reconstructive penile surgery received a caudal injection of 0.25% bupivacaine 0.75 ml.kg−1 with or without morphine 0.05 mg.kg−1. All patients awoke pain-free, but eight of the fifteen patients receiving bupivacaine alone required supplementary injections of opioid postoperatively, whereas none of the patients receiving the bupivacaine-morphine mixture required additional opioids. The incidence of side-effects was similar for the two groups.
Morphine was absorbed rapidly after caudal injection to reach a peak plasma level of 21.2 (±4.8) ng.ml−1 at ten minutes and then fell to 10.1 (±3.8) ng.ml−1 at one hour and 4.1 (±2.6) ng.mh−1 at three hours. These levels are low compared with plasma levels associated with systemic analgesia. We conclude that the extended duration of analgesia from morphine 0.05 mg/kg given caudally is due at least in part to specific spinal analgesia.