Background: The adjunctive use of clonidine to local anaesthetics has been reported to enhance analgesia both after spinal and peripheral administration. However, no attempt has been made to compare spinal and peripheral application of clonidine in the same surgical context in order to further explore the mechanism for the analgesic action of clonidine when administered together with local anaesthetics.
Methods: Using a prospective, randomized, observer-blinded study design, 40 patients, aged 1-7 years, who were undergoing elective surgery for inguinal hernia repair or orchidopexy, were randomly allocated to receive either a caudal block (group C: n = 20; ropivacaine 0.2%, 1 ml.kg-1 + clonidine 2 micro g.kg-1) or an ilioinguinal-iliohypogastric nerve block (group I: n = 20; ropivacaine 0.2%, 0.4 ml.kg-1 + clonidine 2 micro g.kg-1) following the induction of a standardized sevoflurane based anaesthetic. Postoperative analgesia [maximum Objective Pain Scale (OPS) score and requirement for supplemental analgesia] and sedation (three-point scale) were assessed at predetermined intervals during the first 24 h postoperatively.
Results: Fourteen children in group I and nine children in group C did not require rescue analgesia (P = 0.17). No difference in maximum OPS scores could be detected between the two study groups. The mean time to full recovery regarding sedation was 149 min and 153 min in groups C and I, respectively.
Conclusions: This pilot study demonstrates a trend for better postoperative analgesia following peripheral administration of clonidine compared with central application. However, the main mechanism for the adjunct analgesic effect of clonidine when administered together with local anaesthetics requires further study.