Hypothermia: Prevention & Treatment

Summary of Changes

1. Incorporates Tactical Combat Casualty Care (TCCC) Guidelines for Hypothermia from 2021.
2. Expands prevention of trauma-induced hypothermia to include not only trauma patients in hemorrhagic shock, but also burns and cerebrospinal injuries.
3. Outlines characteristics of hypothermia prevention and treatment systems that can be utilized in addition to the more widely used system, the Hypothermia Prevention and Management Kit (HPMK) and the Heat Reflective Shell (HRS).
4. Provides option if unable to remove wet clothing to include the enclosure of the casualty with a vapor barrier over the wet clothing.
5. Recommends upgrading the HPMK to an insulated system as soon as possible as it is non-insulated and therefore only suitable for short term hypothermia prevention.
6. Provides specific target for warm resuscitation fluids/blood products to 38-42 degrees Celsius.
7. Adds Prolonged Casualty Care (PCC) guidelines to the CPG.
8. Expands Field Expedient ‘Tricks of the Trade’ in the CPG.

BACKGROUND

Hypothermia, coagulopathy, and acidosis are the physiological derangements constituting the “triad of death” in trauma patients.1–4 Here, we use the term trauma-induced hypothermia (TIH) as it relates more specifically to combat trauma including hemorrhagic shock, cerebrospinal injury, and burns - all of which lead to a significantly increased risk of mortality and presents as a separate, more severe entity than non-traumatic or environmental hypothermia. TIH is a ubiquitous concern regardless of the environment as it can occur even in warm climates, as has been the experience in the Middle East.5

The Hypothermia CPG, initially published in 2006, was one of the first JTS CPGs. Prior to this, the rate of hypothermia (Temp <97 F) in patients arriving to the first role of care was as high as 15.42% in 2004. The rate initially dropped by over half to 7.26%. While it slowly increased again, it should be noted that missing temperature data in the DoD Trauma Registry (DoDTR) was as high as 42% when large volumes of casualties were being seen in 2003. The rate of missing data dropped significantly when the CPG was published yet remained in the 10-20% range. It is unclear if the true incidence was higher before 2006, but this potentially shows a Hawthorne effect and the effectiveness of tracking information to inform clinical practice. Figure 1 shows the trend in hypothermia by U.S. Military patients by year at any medical treatment facility (MTF). The purpose of this CPG is to provide guidance for the prevention and management of TIH in the combat casualty throughout the escalating roles of care.

#### TIH

TIH is classified as mild: 34-36 °C, moderate: 32-34 °C, and severe: <32 °C.6

Current literature suggests that about one to two-thirds of trauma patients are hypothermic upon presentation to the emergency department. The mortality of hypothermic patients is approximately twice that of similarly injured normothermic patients.7-10 In another large study of trauma patients requiring massive transfusion, hypothermia (< 36 deg C) on arrival was an independent predictor of mortality and associated with increased blood product consumption.11-13 Furthermore, studies in civilian trauma have shown >80% of non-surviving patients arrived hypothermic with a core temperature < 34 deg C.12 In both civilian and military trauma, 100% mortality has been demonstrated when core temperature reached < 32 deg C.14,15 When hypothermic patients fall below the thermoregulatory threshold for shivering (around 30 deg C), shivering heat production ceases. Therefore, these patients have lost the ability to generate heat and will continue to cool unless actively rewarmed by external sources.16 This can be further exacerbated by pharmacologic treatment with sedatives and paralytics.17,18

Innovation and improved outcomes-based research over the past two decades have improved survivability via addressing coagulopathy and acidosis .1,5,19–22 Early recognition and treatment of hypothermia is an equally important consideration that begins at the point of injury and should be implemented for all combat casualties, particularly patients at risk of experiencing shock. As it is labor and resource intensive to re-warm a casualty, measures to prevent hypothermia should begin as soon as possible with thermal wraps and warmed resuscitation products.5,23,24 There are varying degrees of abilities and resources availability at each echelon role of care, which are discussed in the following sections.