COMPARISON BETWEEN PENTAZOCIEN, PETHIDINE AND PLACEBO IN THE TREATMENT OF POST-ANESTHETIC SHIVERING (1999)

S393 INTRODUCTION: Post-anesthetic shivering is a common problem in the recovery room. Pethidine has been shown to be one of the most effective treatments for post-anesthetic shivering. [1]. Although its mechanism of action is not completely understood, a study using naloxone indicated that pethidine may act via kappa rather than mu opioid receptors. The anti-shivering action of pethidine is inhibited by high dose naloxone, which blocks mu and kappa receptors but not by low-dose naloxone which blocks only mu receptors [2]. In order to investigate further the importance of kappa opioid receptors in the treatment of shivering, we have compared the actions of pentazocine and pethidine. Pentazocine 7.5 mg was used, as this is equi-analgesic to pethidine 17.5 mg. As pentazocine is a more specific kappa agonist than pethidine, an equi-analgesic dose should have at least as great an effect on kappa receptors. It should also follow that if pethidine acts principally via kappa receptors in the treatment of shivering, this dose of pentazocine should be at least as effective. METHODS: The study was approved by the local hospital Ethics Committee. We studied 45 patients of both sexes, aged 18 - 63 yr., who developed shivering in the recovery room. All patients were ASA class 1 or 2 and had undergone routine general, orthopedic, plastic or ENT surgery. Routine care for patients in this hospital suffering from postoperative shivering consists of oxygen 6 liter min-1 by mask and covering with a heat reflective blanket. In addition, each patient received an i.v. bolus dose of saline, pethidine 17.5 mg or pentazocine 7.5 mg in a total volume of 2 ml. Syringes containing the drug were prepared by recovery room staff. Tympanic membrane temperature was measured (First Temp GENIUS Thermometer) immediately before giving the drug and shivering was assessed every minute for 10 min. RESULT: Mean temperature at the time of treatment was similar in all three groups: 35.8 (SD 0.6) for placebo, 35.5 (0.8) for the pethidine group and 35.9 (0.9) for the pentazocine group. None of the patients recommenced shivering after they had sopped. After 10 min, 2 patients who had been given pethidine continued to shiver compared with 10 in the group given pentazocine and 13 in the placebo group (Fig. 1). Pethidine was significantly more effective than both of the other treatments. DISCUSSION: We have shown that pentazocine 7.5 mg was not significantly different from placebo in the treatment of post-anesthetic shivering. However, fewer people shivered in the pentazocine group compared with the saline group at every time studied, indicating the possibility that a higher dose may have been more effective. Pethidine may act via delta and/or mu opioid receptors in the treatment of this condition. Pentazocine also binds to delta and mu receptors. It is possible, therefore, that pentazocine, when given in a relatively high dose, acts via delta and/or mu receptors to stop post-anesthetic shivering. In conclusion, we found that pentazocine 7.5 mg did not differ from placebo in the treatment of post-anesthetic shivering. Our results are not consistent with the hypothesis that kappa receptors are more important than mu opioid receptors in the treatment of this condition.