Comparison of Three Strategies for Preventing Hypothermia in Critically Injured Casualties during Aeromedical Evacuation
Critically injured patients are at risk for hypothermia. This study determined the efficacy of three hypothermia prevention strategies: the ChillBuster warming blanket, ChillBuster with a reflective blanket, and two wool blankets. A quasi-experimental design was used to compare changes in core temperature. Following resuscitation from hypovolemic shock, 20 swine were assigned to one of the three interventions, placed in an environmental chamber set to reproduce in-flight conditions onboard a military cargo aircraft (50°F/airspeed 0.2 m/s), and monitored for 6 hours. A repeated measures analysis of variance and least-squared difference post hoc were performed. The ChillBuster/reflective blanket group was significantly warmer than the ChillBuster only group and the wool blanket group.
Under operational conditions, military medical personnel provide patient care In a variety of austere settings including deployable field hospitals, nonmedical buildings, and during aeromedical evacuation (AE) in military cargo aircraft. Since the beginning of Operation Enduring Freedom/Iraqi Freedom, the Air Force AE System and Critical Care Air Transport Teams have transported more than 1,000 critically ill/injured patients. AE may involve patient transport from the combat zone to definitive medical care in Europe and the United States. During these medical flights, which may last from 1 to 14 hours, casualties are exposed to nine stresses of flight.1 These nine stresses include decreased barometric pressure, hypoxia, noise, vibration, gravitational forces, dehydration, third spacing, fatigue, and thermal stress. Thermal stress is the particular focus of this article. Onboard the military cargo aircraft, the temperature decreases dramatically during the first 60 to 90 minutes of flight, reaching an average temperature of 59°F (15°C),2 which may place the casualty at risk for developing hypothermia. Exposure to a cold environment can also occur in a variety of combat environments and hypothermia is a common medical condition encountered in recent combat operations.
In addition to the risk of primary hypothermia due to exposure to a cold environment, trauma victims are at further risk for secondary hypothermia due to an inability to produce body heat because of impaired oxygen consumption.5-7 Body heat production is necessary to maintain normothermia if the ambient temperature is less than 28°C.8 Trauma victims are at further risk for hypothermia because resuscitative measures such as mechanical ventilation and the administration of large volumes of room temperature intravenous (FV) fluids independently cause hypothermia.9 In addition, medications used during patient transport such as sedatives, narcotics, and neuromuscular blockade prevent the warming effect of shivering thermogenesls.
To prevent hypothermia in the AE environment or on a cold battlefield, metabolic heat production and conservation must equal heat loss to the environment. Under conditions where the casualty has impaired thermoregulation and the environmental conditions further exacerbate heat loss, interventions to minimize heat loss and to transfer heat to the body are necessary. The austere environment of care associated with AE operations limits the availability and feasibility of resources to keep patients warm. Interventions typically used in a stateside hospital will not work or are not appropriate for this unique care environment due to Issues such as safety, electrical power requirements, and weight. In addition, field expedient methods such as warming FV fluids with the flameless element on the Meals Ready to Eat has limited utility during long distance transport.19 Based on the risk of hypothermia in combat casualties and the limited utility of many standard wanning devices, there was a need to evaluate alternative methods for preventing hypothermia during the initial field and evacuation phases of care for combat causalities.
The purpose of this study was to determine the efficacy of three hypothermia prevention strategies that are suitable for the operational AE environment. Specifically, this study compared the ChillBuster, the ChillBuster plus a reflective blanket, and two standard military wool blankets. Core body temperature was the measure of the efficacy of each strategy in preventing a decrease in body temperature.