Inadvertent perioperative hypothermia, defined as an involuntary drop in core body temperature to <35°C (95°F), is a condition associated with significant morbidity and mortality.1 This phenomenon has been reported in both emergency orthopedic admissions, such as fracture management, as well as in the elective setting such as arthroscopy, arthroplasty, and spine surgery.
In a study conducted in the United Kingdom including 781 elderly patients with a mean age of 80 years who presented with hip fractures, the 30-day mortality rate was 15.3% in patients who were admitted with a tympanic temperature of <36.5°C and only 5.1% in patients who maintained a tympanic temperature of 36.5°C to 37.5°C (odds ratio, 2.8; P > .0005).2 For an even better perspective, this analysis can be compared with the UK National Hip Fracture Database of 2013, which reported a 30-day mortality of 8.2% in patients who were admitted to the National Health Service with a diagnosis of hip fracture.3
Inadvertent perioperative hypothermia is also a common phenomenon during elective orthopedic hospital admissions. An Australian audit, which included 5050 postoperative patients, looked into the association between inadvertent perioperative hypothermia and mortality based on diagnostic criteria classifying mild hypothermia as a core temperature of <36°C and severe hypothermia as a core temperature of <35°C.4 The authors found that mild and severe hypothermia was experienced by 36% and 6% of patients, respectively. In-hospital mortality was 5.6% for normothermic patients, 8.9% for all hypothermic patients (P < .001), and 14.7% for severely hypothermic patients (P < .001). For a decrease of 1°C in core body temperature from <36°C to <35°C (but >34°C), there were higher odds of in-hospital mortality (odds ratio, 1.83; 95% confidence interval [CI], 1.20-2.60).
The physiologic response to hypothermia is to decrease heat loss by cutaneous and peripheral vasoconstriction and increase heat production by increasing the metabolic rate (eg, shivering and shifting to anaerobic metabolism). This response is blunted to a variable extent in perioperative patients for several reasons, including the effect of anesthetic drugs and old age.5
Maintenance of core body temperature >36°C is now a measured standard of perioperative care. A performance measure for perioperative temperature management was developed by the American Medical Association Physician Consortium for Performance Improvement (AMA-PCPI).6 To achieve this performance measure, mandatory documentation of use of active warming intraoperatively or a record of at least 1 body temperature ≥96.8°F (36°C) within 30 minutes immediately prior to and 15 minutes immediately after anesthesia end time is necessary. This performance measure is also endorsed by the Surgical Care Improvement Project (SCIP-Inf-10) and National Quality Forum (NQF).6
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