Background: In this randomized, triple-blind, placebo-controlled trial, we tested the hypothesis that perioperative acetaminophen administration has a prophylactic effect on postoperative shivering.
Methods: Forty-five women scheduled for gynecological laparotomy were randomized to either the acetaminophen or the placebo groups. After induction of general anesthesia, the test drug (acetaminophen 15 mg/kg) or placebo (0.9% saline) was intravenously administered over 15 minutes. The primary outcome measure was the incidence of severe postoperative shivering (ie, shivering score >2) in the postanesthesia care unit, where patients stayed for 30 minutes after their emergence from anesthesia. For the secondary outcomes, core body temperature (BT) was recorded at the forehead just before anesthesia induction (time 0 [T0]), at the start of surgery (time 1 [T1]), at the end of surgery (time 2 [T2]), at the initiation of postoperative observation in the postanesthesia care unit (time 3 [T3]), and 30 minutes after T3 (time 4 [T4]). At 1 hour after T4 (ie, time 5 [T5]), the BT was recorded from the axilla (BTA). Primary outcome was analyzed using a χ test. BT recorded at the forehead (BTF) and BTA were analyzed using a 2-way repeated-measures analysis of variance (ANOVA) and a 2-sample t test, respectively. For all comparisons, a P value <.05 was considered statistically significant.
Results: The study duration was 2 years. Of the 45 patients initially enrolled, 8 patients were excluded. The acetaminophen and placebo groups included 18 and 19 patients, respectively. The incidence of severe postoperative shivering in the postanesthesia care unit was significantly lower in the acetaminophen group (22.2%) than in the placebo group (73.7%) (relative risk, 0.302; 95% confidence interval, 0.122-0.746; P = .005). Two-way repeated-measures ANOVA showed a significant effect of time (F4,140 = 54.8; P < .001) and a significant time by treatment interaction (F4,140 = 9.61; P < .001) but did not show a main effect of the treatment (F1,35 = 1.83; P = .185) in BTF. Moreover, BTA at T5 was significantly lower in the acetaminophen group (mean [standard deviation {SD}], 37.2°C [0.48°C]) than in the placebo group (37.9°C [0.63°C]; P < .001).
Conclusions: Our findings in patients undergoing gynecological laparotomy suggest that perioperative acetaminophen administration can prevent postoperative severe shivering. This prophylactic effect might be due to suppressing the postoperative increase in the BT set point, rather than lowering the threshold for shivering, as observed with clonidine.