Postoperative Pain Facilitates Nonthermoregulatory

Background: Spontaneous tremor is relatively common in normothermic patients after operation and has been attributed to many causes. The hypothesis that nonthermoregulatory shivering-like tremor is facilitated by postoperative pain was tested. In addition, the effects of intravenous lidocaine on nonthermoregulatory tremor were evaluated. Methods: Patients undergoing knee surgery were anesthetized with 2 mg/kg intravenous fentanyl and 0.2 mg/kg etomidate. Anesthesia was maintained with 1.7 6 0.8% (mean 6 SD) isoflurane. Intraoperative forced-air heating maintained normothermia. The initial 44 patients were randomly allocated to receive an intra-articular injection of 20 ml saline (n 5 23) or lidocaine, 1.5% (n 5 21). The subsequent 30 patients were randomly allocated to receive an intravenous bolus of 250 mg/kg lidocaine followed by an infusion of 13 mg z kg 21 z h 21 lidocaine or an equivalent volume of saline when shivering was observed. Patient-controlled analgesia was provided for all patients: 3.5 mg piritramide, with a lockout interval of 5 min, for an unlimited total dose. Shivering was graded by a blinded investigator using a four-point scale. Pain was assessed by a 100-mm visual analog scale (0 5 no pain and 100 5 worst pain). The arteriovenous shunt status was evaluated with forearmminus-fingertip skin-temperature gradients. Results: Morphometric characteristics and hemodynamic responses were similar in the four groups. Core and mean skin temperature remained constant or increased slightly compared with preoperative values, and postoperative skin-temperature gradients were negative (indicating vasodilation) in nearly all patients. After intra-articular injection of saline, pain scores for the first postoperative hour averaged 46 6 32 mm (mean 6 SD), and 10 of the 23 (43%) patients shivered. In contrast, the pain scores of patients who received intra-articular lidocaine were significantly reduced to 5 6 9 mm and shivering was absent in this group (P < 0.05). In the second portion of the study, neither intravenous lidocaine nor saline reduced the magnitude or duration of nonthermoregulatory tremor or the patients’