The short-lasting analgesia and long-term antihyperalgesic effect of intrathecal clonidine in patients undergoing colonic surgery

In this study, we investigated the antihyperalgesic effect of clonidine after surgery. Sixty patients undergoing right colic resection were studied. Patients were randomized to receive prior to general anesthesia a 2-mL intrathecal (IT) injection of 300 kg of clonidine or saline, or 10 mg of bupivacaine. General anesthesia was achieved using a target concentration propofol infusion and monitored using bispectral index. Postoperative analgesia was provided by morphine IV given through a patient-controlled analgesia device. Postoperative analgesia was assessed by morphine requirements and visual analog scale pain scores at rest, cough, and movement during the first 72 h. Mechanical hyperalgesia was measured by von Frey filaments. Patients were questioned regarding residual pain at 2 wk,l, 6, and 12 mo. The patient-controlled analgesia morphine requirements were significantly smaller in the IT clonidine group (31.5 +/- 12 versus 91 +/- 25.5 and 43 +/- 15 mg, respectively, in groups clonidine, saline, and bupivacaine: P < 0.05 at 72 postoperative hours). The area of hyperalgesia at 72 h was 3 +/- 5 cm(2) in the clonidine group versus 90 +/- 30 and 35 +/- 20 cm(2) in the saline and bupivacaine groups (P < 0.05). At 6 mo, fewer patients in the clonidine group experienced residual pain than in the saline group (0 of 20 versus 6 of 20, P < 0.05). We conclude that both intraoperative spinal clonidine and bupivacaine improve immediate postoperative analgesia. IT clonidine was, however, more potent than IT bupivacaine to reduce postoperative secondary hyperalgesia.