Caudal bupivacaine supplemented with caudal or intravenous clonidine in children undergoing hypospadias repair: a double-blind study

Background. Clonidine is used increasingly in paediatric anaesthetic practice to prolong the duration of action of caudal block with a local anaesthetic agent. Which route of administration of clonidine is the most beneficial remains unknown. We compared the effects of caudal and i.v. clonidine on postoperative analgesia produced by caudal bupivacaine after hypospadias repair. Methods. Forty-six children (ASA I or II) aged 24-104 months received standardized premedication with midazolam, a general anaesthetic and a caudal block with bupivacaine 0.25%, 0.5 ml kg(-1). The children were randomized in a double-blind fashion to two groups: the i.v. group received clonidine 2 mug kg(-1) i.v. and simultaneously the same volume of saline caudally. The caudal group received clonidine 2 mug kg(-1) caudally and a similar volume of saline i.v. After surgery, all children received acetaminophen 20 mg kg(-1) rectally or orally 6-hourly and were given a patient-controlled or nurse-controlled analgesia (PCA/NCA) pump with i.v. morphine (bolus of 25 mug kg(-1) and an 8-min lockout period with no background infusion). Monitoring of scores for pain, sedation, motor block, and postoperative nausea and vomiting was performed by nurses blinded to the study allocations. Time to first activation of the PCA/NCA pump and 0-24 h and 24-48 h morphine consumption were also recorded. Results. Forty-four children completed the study. Age, weight and duration of anaesthesia and surgery were similar in the two groups. The median (range) time to first activation of the PCA/NCA pump was similar in the two groups: 425 (150-1440) min in the i.v. group and 450 (1301440) min in the caudal group. The number of children not requiring postoperative morphine was four and seven respectively. Morphine consumption during 0-24 h and 24-48 h was similar between groups. Conclusions. The analgesic effect of clonidine 2 mug kg(-1) as an adjunct to caudal block with bupivacaine 0.25%, 0.5 ml kg(-1) is similar whether administered i.v. or caudally.