The effects of pethidine, fentanyl and lignocaine on postanaesthetic shivering.

Pethidine is reported to be more effective than equi-analgesic doses of other opioids as an inhibitor of postanaesthetic shivering. The aim of this study was to verify whether this action resulted from a local anaesthetic effect of pethidine or from inadequate fentanyl dosage in previous studies. We studied 52 ASA 1 or 2 patients. They were randomly allocated, in a double-blind fashion, to one of four groups to receive either pethidine (0.85 mg.kg-1) or fentanyl (1.7 micrograms.kg-1) or lignocaine (1 mg.kg-1) or 0.9% saline. All the patients were shivering and had a core temperature below 36 degrees C during recovery from non-septic abdominal or orthopaedic surgery. After 15 min, all the patients given saline were still shivering, as were 92% in the lignocaine group. In contrast, only 23% of the patients who were given fentanyl still shivered (p < 0.01 versus saline) and 8% in the pethidine group (p < 0.001 versus saline). The mean (SD) core temperature in the pethidine group was slightly lower than that in the fentanyl group (35.1 (0.6) and 35.9 (0.5)) when the patients stopped shivering. Furthermore, shivering restarted in 6/10 patients in the fentanyl group after 15 min compared with 1/12 in the pethidine group. Our results show that fentanyl (1.7 micrograms.kg-1) can inhibit postanaesthetic shivering but this effect is less pronounced and of shorter duration than with pethidine (0.85 mg.kg-1).