Prevention of perioperative hypothermia is a core measure to improve the outcome after ambulatory and fast-track orthopedic surgery and rehabilitation. Preventive strategies for perioperative hypothermia can be grouped into passive heat retention methods and active external warming methods (Table 2). Passive methods aim to maintain body temperature by decreasing the heat loss by radiation (eg, reflective blanket), conduction (eg, layered cotton blankets and padding the operating table), or convection (eg, heat and humidity exchanger in the breathing circuits) to the surrounding environment. Active patient heating methods aim to bring in heat from the source to the patient’s body using conduction (eg, Hot Dog® [Eden Augustine Temperature Management]) or convection (eg, Bair Hugger® [Arizant Healthcare]) techniques.
Table 2. Methods to Prevent Inadvertent Perioperative Hypothermia
Passive Heat-Retention Methods
Active External Warming Methods
Active patient warming is superior to passive heat retention methods. A recent Cochrane study assessed the effects of standard care (ie, use of layered clothing and warm blankets, etc.) and addition of extra thermal insulation by reflective blankets or active forced air warming to standard care on the perioperative core body temperature.19 They concluded that there is no clear benefit of addition of extra thermal insulation by reflective blankets compared with standard care alone. Also, forced-air warming in addition to standard care appeared to maintain core temperature better than standard care alone, by between 0.5°C and 1°C, but the clinical importance of this difference could not be inferred, as none of the included studies in this meta-analysis documented major cardiovascular outcomes.
Several clinical guidelines have been developed by not-for-profit, government, and professional organizations aimed at prevention of perioperative hypothermia as primary or secondary outcome. A clinical guideline was published by ASPAN in 2001 for assessment, prevention, and intervention in unplanned perioperative hypothermia.14 Cost and time effectiveness of the ASPAN Hypothermia Guideline was published in 2008.20 The assessment guideline includes identification of risk factors, repeated pre-/intra-/postoperative temperature measurement, and repeated clinical evaluation of the patient’s status. The preventive guideline is to maintain an ambient temperature of 20°C to 24°C (68°F-75°F) and use appropriate passive patient warming methods pre-, intra-, and postoperatively. Intervention in the form of active patient heating is advised only if the patient develops hypothermia in spite of the above-mentioned standard preventive measures. But many orthopedic ambulatory surgery centers currently use active patient warming as both a preventive and an intervention strategy.
Active patient warming by conduction devices occurs by direct physical contact with the device, which is set at a higher temperature, whereas heat transfer from the convection device to the patient occurs by a physical medium such as forced air or circulating water that moves in between the device and the patient. Any recommendation for use of a specific technique of active patient warming (ie, by the use of a conduction device or a convection device) should only be given after comparing evidence on 3 critical aspects: efficacy, safety, and cost effectiveness.
The heating efficacy and core rewarming rates of conduction and convection devices have been compared in the literature. Full-body forced-air heating with the Bair Hugger® and full-body resistive polymer heating with the Hot Dog® in healthy volunteers were found to be similar.21 Also, in a randomized study conducted on 80 orthopedic patients undergoing surgery, resistive polymer warming performed as efficiently as forced-air warming in patients undergoing orthopedic surgery.22
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