The use of forced air warmer for the prevention of inadvertent perioperative hypothermia under general anaesthesia - A prospective observational study

Abstract

Temperature is an important parameter which determines patient outcomes perioperatively. Iatrogenic hypothermia during surgery under general anaesthesia leads to significant side effects which can be corrected with the use of active body surface warming devices like the forced air warmer. A prospective observational study was conducted with a sample size of 362 which included patients of either sex aged 18-65years posted for any elective surgery under general anaesthesia lasting >60 and ≤180minutes. Baseline oral temperature was recorded preoperatively. Patients were warmed with forced air warmer intraoperatively at 44°C with half hourly monitoring of nasopharyngeal temperature until extubation. Intravenous fluids were given at room temperature. Further, oral temperature was monitored at 15 and 60 minutes in post anaesthesia care unit and patients were warmed if hypothermic or shivering. The final mean intraoperative temperature (nasopharyngeal) was 36.01⁰C (n=362) with a range from 34.7⁰C to 37.1⁰C. 139 of 362(n) (38.4%) patients were hypothermic (<36⁰C) at the end of surgery. 61.6% of patients were normothermic. In 9 patients (2.5%, n=362) the forced air warmer was turned off due to over heating (temperature >37⁰C). 33 patients (n=362, 9.1%) had shivering postoperatively. Comparing the nasopharyngeal temperature (mean) at half hourly intervals post induction revealed statistically significant results (p<0.001). The establishment of near constant temperature (36±0.03°C) following the initial fall in core body temperature can be attributed to the forced air warmer. However, it is imperative to continuously monitor core body temperature to detect temperature changes(hypo/hyperthermia) in order to use the device safely as chances of overheating is always present.