Thermal management during anaesthesia and thermoregulation standards for the prevention of inadvertent perioperative hypothermia

A recently published European survey revealed that intraoperative temperature monitoring is widely neglected, and only 39% of all patients were actively warmed. Evidence-based practice guidelines to prevent inadvertent perioperative hypothermia are warranted with reference to clinical queries: temperature measurement, definition of hypothermia, risk factors, warming methods, and implementation strategies. Currently the following advice can be given. (1) Mean normal human core body temperature is 37 °C. Systematic review found that non-invasive oral measurement is valid and reliable for core temperature determination, also pre- and postoperatively, in contrast to infrared ear temperature, which should be omitted. Intraoperatively, nasopharyngeal/oral, oesophageal, urinary bladder or rectal measurements are alternatives, depending on specific limitations and site of surgery. Temperature should be monitored continuously in all anaesthesias longer than 30 min for adults, but in all children regardless of duration. (2) Clinically relevant hypothermia starts at 36 °C with regard to major adverse outcomes (cardiac and coagulation disorders and infectious complications). (3) Pre-warming effectively minimizes initial redistribution hypothermia and should be established for 20 min immediately before induction of anaesthesia. (4) Active warming methods are necessary to maintain normothermia. Amongst these methods, forced-air warming is the safest (no contamination of the wound) and most effective, provided that enough skin surface is available. Multipart circulating water garments are also effective, although they are bulkier and there is a risk of water leakage. Fluid warming is only effective when large amounts are given. (5) For implementation protocols, postoperative temperatures and outcomes should be recorded. Patients should be informed, and continuous education of staff should focus on periodically updated evidence-based perioperative thermoregulatory guidelines which reflect on current diagnostic and therapeutic tools.