Page 27 - JSOM Fall 2020

TABLE 2 Cont.
Rewarming Level of
Prehospital Reference Effectiveness Evidence a Comments
HPMK Allen et al. 61 √√√ C Prospective randomized study. Did not use human
volunteers, but simulated torso with fluid bladder
system. Effective outcome compared with all active
heating systems studied.
CoTCCC, JTTS, and DoD preferred system since
2006; outer vapor-barrier garment and 10-hour
(110°F) chemical blanket; low cost, weight, and size;
effective system only for short-term use due to lack of
insulation; patients will get cold in <60 min; use in cold
environments 22
Improvised Dutta et al. 22 √√√√ B Randomized controlled study with human volunteers.
hypothermia wrap The user-assembled and Doctor Down systems were
(user-assembled most effective.
Active system)
Rewarming Doctor Down Dutta et al. 22 √√√√ B
Methods Rescue Wrap
(cont.)
HPMK Dutta et al. 22 √√ B Randomized control study with human volunteers.
HPMK was least effective because of lack of insulation.
MARSARS Dutta et al. 22 √√√ B Randomized control study with human volunteers.
Hypothermia These two systems were not as effective for retaining
Stabilizer Bag thermal balance when compared with the DD and user-
assembled system systems.
Wiggy’s Victim Dutta et al. 22 √√√ B
Casualty Bag
Ready-Heat Phillips et al. 77 √√√ C Single case report with high efficiency to rewarm
Blanket and patient
PrimaLoft synthetic
sleeping bag
hypothermia wrap
Abbreviations: √, mildly effective; √√, moderately effective; √√√, highly effective; BB, Blizzard Blanket; CoTCCC, Committee on Tactical Com-
bat Casualty Care; DoD, Department of Defense; HP, Hot Pocket; HRP, human remains pouch; HRS, heat-reflective shell; IO, intraosseous;
IV, intravenous; JTTS, Joint Theater Trauma System; MEDEVAC, medical evacuation; NE, not effective; SB, space blanket; WB, wool blanket.
a Level A: Evidence from multiple randomized trials or meta-analyses. Level B: Evidence from a single randomized trial or non-randomized
studies. Level C: Expert opinion, case studies, or standards of care. 70

of an outer layer (e.g., a tarp), ground insulation pad(s), and underwear with a vapor barrier wrapped around the manikin;
one to three sleeping bags. When multiple sleeping bags are and (5) no underwear. Heat loss and thermal resistance were
available, each bag should be placed within each other to cre- determined from continuous monitoring of ambient air tem-
ate a multilayered insulation with the patient placed inside the perature, manikin surface temperature, heat flux, and evapo-
innermost bag. For maximum insulation around the patient, rative mass loss rate. The authors reported that independent
each bag should be completely zipped up to prevent any cold of insulation thickness or ambient temperature, the removal
spots on the sides of the bags, and an outer waterproof layer of wet clothing or the addition of a vapor barrier over the wet
wrapped around all layers to prevent body heat loss while clothing resulted in a reduction in total heat loss of 19% to
blocking wind and moisture entry. 17 42%. These findings were subsequently validated in human
volunteers and confirmed equal benefit for either removing
When hypothermic patients (core temperature <28°C [82.4°F]) wet clothing and providing one blanket for insulation, or leav-
are below the thermoregulatory threshold for shivering (~30°C ing wet clothes intact and wrapping a vapor barrier around
[86°F]), shivering heat production ceases. 23,25 Thus, these pri- the patient. These two-treatment conditions both significantly
mary hypothermic patients will continue to cool, and they can- decreased metabolic rate, increased skin temperature, and
not warm up spontaneously without external heat, even if they decreased shivering thermogenesis, resulting in an overall im-
are well insulated from the environment; this is especially true provement of the patient’s thermal stress. 66
for trauma patients. During prehospital trauma management,
the administration of pain medications, such as ketamine, opi- Given this evidence, prompt treatment with active rewarming
oids, and benzodiazepines, per TCCC guidelines, may abol- is now recommended in both Prehospital Trauma Life Support
ish shivering, which can further exacerbate the magnitude of (civilian and military versions) and Advance Trauma Life Sup-
hypothermia. 71,72 port trauma management guidelines. 73,74

The benefits of removing wet clothing and improving thermal Q1. Is adding an external heat source to a hypothermia
balance were reported in a study that used a thermal manikin wrap effective?
to evaluate three different insulation ensembles consisting of Many studies have evaluated the effectiveness of external heat
one, two, or seven wool blankets. Additionally, five different sources in transferring heat to the body. 17,57 A variety of heat
65
test conditions were evaluated for all three levels of insula- sources have been reviewed, including electrical and chemical
tion: (1) dry underwear; (2) dry underwear with a vapor bar- heating pads/blankets of various sizes, warmed water bottles,
rier wrapped around the manikin; (3) wet underwear; (4) wet hot water bottles or bags, charcoal-burning heat packs, and

Management of Hypothermia in Tactical Combat Casualty Care | 25