A study on the effect of preoperative warming on post-induction core temperature and incidence of postoperative shivering in patients under general anesthesia

Abstract

Background Inadvertent perioperative hypothermia (IPH) defined as core temperature below 36.0 °C is a common complication of general anesthesia with prevalence up to 70%. Warming of peripheral tissues prior to induction of anesthesia reduces the central to peripheral temperature gradient, thereby minimizing central heat loss due to heat redistribution, after induction of anesthesia. This study aimed to evaluate the effect of prewarming on post-induction core temperature and incidence of perioperative inadvertent hypothermia leading to postanesthetic shivering (PAS) in patients undergoing general anesthesia. This is a single-arm study performed after authorization from the scientific review committee (IRB no.:10/2015/05) in a cohort of patients between the ages of 18 and 65 years in ASA I and II physical status, undergoing GA for elective surgeries lasting less than 3 h. Rates of IPH and PAS in 60 patients who were warmed before anesthesia over a 30-min period with a forced-air warmer set at 38.0 °C were compared with existing data from an equal number of cohorts who received only intraoperative warming, during similar surgical procedures according to routine GA. Comparisons between the two groups were made using the Student’s t-test and chi-square test. A paired t-test or Wilcoxon’s signed rank test was applied for pairwise comparisons. The results were considered statistically significant when the P-value was < 0.05. Results The mean decrease in core temperature in the unwarmed group was 0.7 °C (+ /- 0.23) compared with a 0.2 °C decrease (+ /- 0.06) in the prewarmed group of patients. A total of 31.70% of patients in the unwarmed group developed IPH compared with one patient (1.7%) in the prewarmed group shortly after onset. Twenty-six patients (43.30%) in the unwarmed group had hypothermia at the end of surgery, compared with one patient (1.7%) in the prewarmed group. Shivering was observed in 46% of patients in the unwarmed group, while no shivering was observed in the prewarmed group. Conclusions Preoperative warming is an effective intervention to reduce the frequency of core temperature drops after induction of anesthesia, thereby preventing inadvertent perioperative hypothermia and the incidence of postoperative shivering.