Intra-operative hypothermia, defined as a core body temperature of <36°C, is frequently observed during surgery [1]. In 2016, the National Institutes of Health and Care Excellence updated its guidelines on preventing inadvertent intra-operative hypothermia. Active warming is recommended if the surgical duration is >30 min, the patient’s body temperature is <36°C and the temperature is maintained at >36.5°C [2]. The risks of hypothermia include surgical site infections, coagulopathy, need for increased transfusion, pain, adverse cardiac events, prolonged post-anesthetic recovery and decreased thermal comfort 1, 3, 4, 5, 6.
The main thermoregulatory mechanisms that maintain normal body temperatures in humans are sweating, vasoconstriction and shivering. [7] Anesthesia impairs thermoregulation by decreasing vasoconstriction and shivering thresholds. The extent of this effect is dose-dependent and synergistic when a combination of drugs is used. The vasoconstriction threshold may decrease to approximately 34.5°C during surgery. [7] Within the first hour after anesthesia induction, hypothermia is caused by core-to-periphery temperature redistribution because of the vasodilatory effects of anesthesia . Maintaining normothermia aims at preventing redistributive heat loss and active rewarming to manage the lowered thermoregulatory thresholds.
Patients who undergo degenerative spine surgery are typically older and at high risk for intra-operative hypothermia [8]. While mild hypothermia occurs during anesthesia and surgery [9], it should not be accepted as the norm. Normothermia should be vigorously maintained. The consensus for enhanced recovery after surgery (ERAS) for lumbar spinal fusion strongly recommends maintaining normothermia [10].
Several options are available for maintaining normothermia. Active forced-air warming (FAW) devices are superior to circulating water mattresses 11, 12. In current practice, the FAW device is placed either over the lower limbs or upper body in the prone position during spine surgery. However, a significant temperature decline can still occur [13] during the preparation stage if a large portion of the patient’s skin is exposed to the cold ambient temperature.
At our institution, a single FAW device is used for routine spine surgeries, and dual FAW devices are used for spine ERAS. This study aimed to investigate the intra-operative body temperature changes between single and dual FAW devices via propensity score matching. We hypothesized that the use of dual FAW devices can improve intra-operative body temperature management in lumbar spine surgeries by increasing the body surface area coverage of active warming. Temperature changes were analyzed with the time-temperature integral (TTI) method to better describe the temporal and magnitude of changes in temperature management.
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