Thoracic epidural clonidine and morphine for postoperative pain relief.

This study was undertaken to evaluate the potentiation of the postoperative analgesic effect of thoracic epidural morphine by coadministration of thoracic epidural clonidine in a randomized double-blinded design. Twenty patients underwent radical gastrectomy under combined general anaesthesia (enflurane and nitrous oxide/oxygen) and epidural anaesthesia with local anaesthetics. They received a thoracic epidural bolus injection of either 0.05 mg.kg-1 morphine plus 3 micrograms.kg-1 clonidine (M+C group; n = 10) or 0.05 mg.kg-1 morphine alone (M group; n = 10) immediately before completion of surgery. All patients received iv morphine via patient-controlled analgesia (PCA) equipment for 24 hr postoperative period, and the PCA iv consumption of morphine was the primary variable of efficacy of the analgesic regimen. In addition, data analyses included mean arterial blood pressure, heart rate, respiratory rate, arterial blood gas measurement, sedation score, and visual analogue pain scale score (VAS). The cumulative number of iv morphine injections via PCA was less in the M+C group than in the M group at each hour for 24 hr postoperative period (P < 0.05), while the numbers of PCA morphine injections per hour beyond nine hours after surgery were higher in the M group than in the M+C group (P < 0.05). Sedation score was higher, and VAS and mean blood pressure were lower in the M+C group only at one hour after surgery compared with the M group. We conclude that the combined single thoracic epidural administration of morphine plus clonidine produces a more potent and longer lasting analgesia than does morphine alone.