Comparison of pethidine and clonidine in the prevention of postoperative shivering. A prospective, randomised, placebo-controlled, double-blind study.

Patients with ischaemic heart disease and cardiac failure are endangered by an increase in oxygen consumption caused by postoperative shivering. The purpose of this study was to evaluate if pethidine and clonidine, which are well known for their effectiveness in the treatment of this undesirable side effect, can also prevent postoperative shivering if administered at the end of surgery. In addition it was investigated whether their intraoperative application influences the time of extubation and analgesics demand in the early postoperative period. Methods: 60 patients (ASA I-II) scheduled for elective microsurgical vertebral disc resection were included in the study. After standardised induction of anaesthesia (5 mgxkg(-1) thiopental, 2 mu gxkg(-1) fentanyl, 0.1 mgxkg(-1) vecuronium) lungs were ventilated with isoflurane vaporised in 66% N2O and 33% O-2. The concentration of the inhalation anaesthetic was adjusted to maintain a surgical plane of anaesthesia without supplementary doses of opioids. Patients were randomly allocated in a double-blind fashion to one of three groups (each n = 20) to receive either pethidine (0.3 mgxkg(-1)) or clonidine (2 mu gxkg(-1)) or 0.9% saline (control) 5 minutes prior to the end of surgery. Heart rate, arterial blood pressure and rectal temperature were measured at defined times, as well as the recovery time between the end of anaesthesia and extubation, incidence of postoperative shivering, and the pain level of the patients with a visual analog scale. The frequency and total demand of analgesics were determined using patient controlled analgesia and recorded for two hours postoperatively. Results: The incidence of postoperative shivering in the clonidine group (5%) was less than in the pethidine group (25%) and significantly less than in the saline group (55%). Heart rate and blood pressure values after the administration of clonidine were lower than after pethidine and significantly lower than after saline. The time between end of surgery and extubation was similar in all groups with an average of 18 minutes. No significant differences among the pain scores and the analgesics demand were noted among any of the groups, including the saline control-group. Conclusion: Intraoperative administration of clonidine (2 mu gxkg(-1)) is suitable for prevention of postoperative shivering. Despite its sedative effects the recovery time until extubation was not prolonged. 0.3 mgxkg(-1) pethidine proved to be less beneficial.