NON-THERMOREGULATORY SHIVERING IN PATIENTS RECOVERING FROM ISOFLURANEOF DESFLURANE ANESTHESIA

Background Although cold-induced shivering is an obvious source of pos tanesthetic tremor, other causes may contribute. Consistent with this theory, the authors had previously identified an abnormal clonic compo nent of postoperative shivering and proposed that it might be nontherm oregulatory. A subsequent study, however, failed to identify spontaneo us muscular activity in normothermic volunteers. These data suggested that the initial theory was erroneous or that a yet-to-be identified f actor associated with surgery might facilitate shivering in patients a fter operation. Therefore, the authors tested the hypothesis that some postoperative tremor is nonthermoregulatory. Methods: One hundred twe nty patients undergoing major orthopedic operation were observed. They were grouped randomly to receive maintenance anesthesia with nitrous oxide and isoflurane (0.8 +/- 0.4%) or desflurane (3.4 +/- 1.1%). Twen ty patients in each group were allowed to become hypothermic, whereas normal body temperatures were maintained in the others (tympanic membr ane temperature exceeding preinduction values). Arteriovenous shunt va soconstriction was evaluated using forearm-minus-fingertip skin-temper ature gradients; gradients less than 0 degrees C identified vasodilati on. Postanesthetic shivering was graded by a blinded investigator. Tre mor in patients who were normothermic and vasodilated was considered n onthermoregulatory. Results: Thermoregulatory responses were similar a fter isoflurane or desflurane anesthesia. Approximately 50% of the unw armed patients shivered. Shivering was observed In 27% of the patients who were normothermic; 55% of this spontaneous muscular activity occu rred in vasodilated patients. Among the normothermic patients, 15% ful filled the authors' criteria for nonthermoregulatory tremor.Conclusion s: The incidence of postoperative shivering is inversely related to co re temperature. Therefore, it was not surprising that shivering was mo st common among the hypothermic patients. The major findings, however, were that shivering remained common even among patients who mere kept scrupulously normothermic and that many shivered while they were vaso dilated. Thus, postoperative patients differ from nonsurgical voluntee rs in demonstrating a substantial incidence of nonthermoregulatory tre mor.