Page 24 - JSOM Fall 2020

high rate of hypothermia in combat casualties. The use of active warming techniques in the prehospital environment to
a commercial device that included an external heat source prevent hypothermia in severely burned patients. 32,34,35
(Hypothermia Prevention and Management Kit [HPMK];
North American Rescue, http://www.narescue.com) was One potential risk factor for hypothermia is active cooling of
recommended. 20,21 extensive TBSA burns. It has been generally recommended to
(3) A recent publication supported the effectiveness of the limit cooling to small burns to avoid accelerating convective
HPMK as an enclosure system for rapid application; how- heat loss, which is likely to occur with large TBSA burns. The
ever, it was ranked last in objective (physiological heat relationship of burn cooling and hypothermia in the prehospi-
transfer and balance indices) and subjective (human vol- tal setting has not always been found in retrospective studies
unteers ranking each enclosure system) measures, com- independent of methods used to cool. 33,36,37 However, in burn
pared with four other hypothermia enclosure systems management of combat casualties, as a comorbidity of trauma,
when evaluated in a 60-minute cold chamber study at extensive TBSA burns can independently cause hypothermia
−22°C (−7.6°F). 22 and death, and this relationship becomes synergistic with pol-
(4) Feedback from the field indicates that the HPMK (a non- ytrauma, anesthetized, and artificially ventilated patients when
insulated enclosure [cover] with chemical heating blanket) in cold climates. Thus, it is essential to prevent and manage
33
has limitations keeping casualties warm during cold- hypothermia in all types of trauma and to cool the burn initially,
weather use. Other commercially available hypothermia and not the patient, by avoiding uncontrolled burn cooling. 37
prevention products and rewarming techniques may work
better than the HPMK used alone. By providing other val- Civilian and military trauma centers have linked TIH and co-
idated hypothermia-prevention methods, medics will have agulopathy on arrival with increased mortality. 7,8,38,39 Acute
additional options for casualty rewarming as they advance traumatic coagulopathy (ATC) is a complex, multifactorial
through the phases of casualty care or into prolonged field process involving biochemical and physiological changes. Re-
care. cent descriptions of this pathophysiological cascade have fo-
(5) Current CoTCCC hypothermia guidelines do not provide cused on the underlying mechanisms of coagulopathy. 12,39,40–42
recommendations for insulated rewarming enclosure sys- In general, there are six primary mechanisms contributing to
tem options for casualties in cold environments. ATC: tissue trauma, shock, hemodilution, hypothermia, aci-
(6) Current CoTCCC hypothermia prevention guidelines do demia, and inflammation. Consequently, patients with TIH
40
not mention the use of battery-powered intravenous (IV) have a worse prognosis and increased mortality rate compared
blood/fluid warming devices with ideal output tempera- with patients with primary hypothermia who have compara-
ture and flow rates. Furthermore, current Food and Drug ble decreases in core temperature. 13,43,44
Administration (FDA)-approved, portable fluid-warming
devices have large variance in output temperature. Eastridge et al. retrospectively reviewed >1,100 combat ca-
9
sualties presenting to surgical support hospitals during Op-
eration Iraqi Freedom from January to July 2004 and found
Background 44
that the TIH mortality rate was twice that of normothermic
Primary hypothermia is defined as the involuntary drop in body casualties with similar injuries. TIH is not unique to combat
45
core temperature (i.e., of the heart, lungs, and brain) below a casualties. The majority of the TIH studies emanated from
13
core temperature of 35°C (95°F). The associated pathophysi- civilian trauma and mostly were reported beginning in the
ology and clinical management have been well described. 17,23–27 1980s. 6,45–47 Retrospective and prospective studies reported the
Primary hypothermia occurs in healthy individuals when the relationship among trauma, hypothermia, coagulopathy, and
body’s heat production is overcome by excessive cold exposure increased mortality. Hemorrhagic shock leads to decreased
in air or water. In contrast, hypothermia secondary to trauma metabolic heat production and uncouples normal metabolic
(i.e., trauma-induced hypothermia) is associated with hem- pathways, such as the clotting cascade. Hypothermia is com-
orrhagic shock and cerebrospinal injury and destabilizes the mon in trauma patients, with approximately 40% to 50% of
body’s thermoregulatory capacity. TIH can occur even in very moderate to severely injured patients arriving in a hypothermic
warm climates. The CoTCCC hypothermia update focuses on state at civilian hospitals and >80% of nonsurviving patients
TIH to strengthen the current recommendations for preven- arriving with a core temperature <34°C (93°F). 48,49 In both ci-
tion and management in combat casualties. vilian and military trauma, it has been reported that 100%
mortality occurred when core temperature is <32°C (89.6F). 6,7
Hypothermia is one leg of the “lethal triad” caused by a vicious
metabolic cycle of tissue hypoperfusion causing decreased ATP Based on the difference in mortality between primary hypo-
production, which leads to hypothermia, coagulopathy, and thermia and TIH, the hypothermia classification specific to
acidosis; this is associated with increased mortality. 28–30 In trauma begins at <36°C (96.8°F) (Table 1).
burn patients, a similar relationship exists between hypother-
mia in the lethal triad and worse patient outcomes. 31–33 In burn The early recognition and prevention of hypothermia are
patients (≥20% total body surface area [TBSA]), hypothermia essential during casualty assessment and care in battlefield
on hospital admission is directly linked to increased mortal- trauma. Hypothermia interventions should be implemented
ity. In a retrospective study, risk factors for burn-related hy- for every patient in shock or at risk of shock. Prevention of
32
pothermia are: extensive TBSA (>33%), full-thickness burns, additional heat loss can be achieved with the use of a hypo-
and inhalation injury. The authors concluded that beginning thermia wrap either without (passive) or with (active) an ex-
33
in the prehospital setting, patients with severe burn trauma ternal heat source, and warming all infused fluids.
benefit from any methods to prevent heat loss and, when pos-
sible, use of an active, external, warming enclosure system. Another essential hypothermia intervention is restoration of
Other burn-related trauma studies also recommend using blood volume by transfusing warm whole blood or blood

22 | JSOM Volume 20, Edition 3 / Fall 2020