Page 33 - JSOM Fall 2020

manufacturers of fluid- and blood-warming devices regarding FIGURE 3 Preferred method to create an insulated Hypothermia
any risk of aluminum toxicity. Prevention, and Management Kit for hypothermia heated wrap (a
cross-sectional view: heat-reflective shell outer layer to inner layer
Ready-Heat Blanket over casualty).
Conclusion
Recent research on the enFlow warmer device show elevated
™
aluminum level in IV fluid after it passes through the uncoated
aluminum heating plate in this device. No other portable
warming device has a similar warming-plate system with alu-
minum contacting blood. Level of evidence: B

Hemolysis
Current, FDA-approved, portable IV warming devices use a
heating plate that comes in direct contact with the fluid. One
concern is that rapid heating and the coating agent used in
the heating plate can cause RBC damage. Heating RBCs to
>42°C will cause cell injury and hemolysis. 104–106 However,
when studies evaluate warming blood between 38°C and 42°C
(100°F–108°F) with either a hospital electrical AC-powered IV
warming device or portable battery-powered IV warming de-
vice, there is no evidence of RBC damage at or below this tem- Alternatively, when no HPMK is immediately available to cre-
perature range. 107–109 Poder et al. conducted a meta- analysis of ate an insulated HPMK, there is good evidence for how best
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17 observational studies on hemolysis with blood heating. The to create an effective improvised hypothermia enclosure sys-
descriptive analysis indicated that multiple factors can influence tem, as mentioned previously. See Figure 4 for cross-sectional
the level of hemolysis during blood heating, including blood layers of an improvised insulated hypothermia wrap. When a
age, anticoagulant type, and duration of exposure to heat. They sleeping bag is not immediately available, due to operational
concluded that at temperatures of ≤43°C (109°F) and even up logistics, use at least two wool blankets wrapped around the
to 45°C–46°C (113°F–115°F), blood heating is safe and hemo- casualty. If no insulation is readily available at the POI, apply
lysis, as indicated by free hemoglobin, is negligible. the HPMK to the casualty, as originally recommended.

Conclusion FIGURE 4 An improvised, insulated, hypothermia heated wrap (a
The risk of hemolysis when administering blood with a cross-sectional view outer layer to inner layer).
battery-powered warming device is clinically negligible with
blood warmed to 42°C (108°F), which is higher than the rec-
ommended output temperature by the Joint Trauma System
damage-control resuscitation guideline. Level of evidence: B

Implications for TCCC
It is now evident that there are limitations when using the nonin-
sulated HMPK in cold environments. These data are supported
by feedback from the field in various Special Operations Forces
units who already have begun transitioning to an insulated and
external heat-source enclosure system for better thermal pro-
tection and patient comfort. Improved hypothermia enclosure
systems can be transitioned to the US military by implementing
the most effective, logistically supportable, and evidence-based
rewarming methods as a solution to the current limitation of
the noninsulated HPMK by using either (1) HPMK with added
insulation, (2) an improvised hypothermia enclosure system us- Summary
ing high-quality insulation and heat source, or (3) a commercial
hypothermia enclosure system for combat casualties with TIH The HPMK has worked well since implementation when used
or burn trauma–related hypothermia during initial treatment for initial casualty management and rapid transition to med-
and during prolonged field care and evacuation. It is essential to ical treatment facilities, and the HPMK has the best evidence
anticipate, plan, prepare, and train for TIH and implement an to date for effectiveness as a hypothermia enclosure system for
effective hypothermia enclosure system as soon as possible after the majority of operational applications. However, the HPMK
injury. The benefit to the US Department of Defense is that potentially has limitations in maintaining thermal balance in
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the user-assembled hypothermia enclosure system is a low-cost cold environments, due to the lack of insulation. In situations
insulation option and can be improvised with a hooded sleep- that may result in prolonged exposure of a casualty to a cold
ing bag (various weight, size, and styles), or by using an RHS environment, it is essential to provide insulation inside the
with an internal vapor barrier, two or more wool blankets, or shell of the HPMK (preferably with a hooded sleeping bag or
other readily available insulation material and an RHB as one other readily available insulation materials). When no HPMK
proposed insulation modification with the HPMK. See Figure is available, responders should assemble an improvised hy-
3 for the cross-sectional layers of the recommended method to pothermia enclosure system that contains a hooded sleeping
create an insulated HPMK with a hooded sleeping bag. bag (preferred), wool blankets, or cold-weather issue gear

Management of Hypothermia in Tactical Combat Casualty Care | 31