Impact of Heating Inspired Gases During Mechanical Ventilation on Resolution of Hypothermia in a Porcine Model

Hypothermia is a common finding following prehospital trauma with important consequences. Treatment includes removal of the patient from exposure and application of a vapor barrier and blankets. The role of elevated inspired airway temperatures for rewarming has been advocated for decades with little evidence of benefit. We sought to determine if warming of inspired gas up to 44°C will increase core temperature to normothermia after hypothermia as compared with standard of care warming.

Female swine, 39.0 ± 2.5 kg, were orally intubated and placed on a mechanical ventilator (R860, GE Healthcare, Chicago, IL) with the plane of anesthesia maintained via intravenous (IV) propofol infusion. A heat and moisture exchanger (HME) was used for airway humidification and baseline measurements for all animals. After baseline vital signs, airway temperature, and core body temperature were recorded, a simulated hemorrhage was completed via a peristaltic pump. Blood was withdrawn at 1 mL/kg/min until 20% of total calculated blood volume was reached. Shed blood was anticoagulated and retained for later use. Active cooling was the accomplished via Arctic Sun 5000 Temperature Management System. Animals were then randomized to 1 of 4 warming methods: heated humidifier (HH) set at 37°C; HH set at 44°C; HME alone, and HME with warm fluids IV infusion, with 6 animals per group. Animals were wrapped in a mylar thermal blanket, warmed per the randomized warming method, and monitored for 4 hours.

The use of inspired gas temperatures up to 44°C was associated with a small increase (1.5°C) in core body temperature compared with an HME alone. However, none of the methods of rewarming returned animals to the baseline temperature after 4 hours.

Active humidification with supranormal temperatures had minimal impact on core body temperature following 4 hours of treatment.