Page 15 - JSOM Spring 2023

uncovered an extremity about which a tourniquet had been may plausibly risk a burned limb even if it has a cold injury.
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applied and never to employ artificial means to warm it. At Cold-injured limbs have had local heat injury caused by such
the end of World War II, a US Army medical bulletin included heaters. 113,114
guidance that a limb with a tourniquet applied should have its
temperature lowered as much as feasible, short of actual freez- Tourniquet use guidelines in extreme cold weather are absent
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ing. In 1950, a military report of an arctic exercise advised to presently, whereas they existed previously. Guidelines need to
“stop hemorrhage first: Tourniquet, pressure points, and ban- be reviewed for possible updates to account for an associa-
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dage.” It then noted: “If tourniquet is applied, remember that tion between tourniquet use and frostbite risk. A graded guid-
heat is also shut off to [the] injured member [limb]. Freezing ance based on end-user ability may be needed—for example,
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will result unless external heat is applied.” A military physi- no update for lay first-aiders, a minor update for medics, and
cian with field experience in combat noted in post-war instruc- a major update for nurses and doctors. A new guideline for
tion that, “During cold weather an extremity with a tourniquet tourniquet uses in extreme cold weather is a suitable topic for
applied is unusually susceptible to freezing and gangrene for- a research priority list in combat casualty care. Treatment op-
mation. During the freezing months the aidmen and surgeon tions and guidelines in how prehospital emergency caregivers
should be unusually careful not to apply a tourniquet unless it are to thermally manage injured limbs is a topic in need of
is absolutely necessary and should do so only when repeated research and development—for example, how a paramedic is
efforts to control hemorrhage have failed.” However, despite to keep a limb from freezing while not overheating it. Limb
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sources acknowledging a tourniquet risk of hastened freezing cooling in a warm environment has potential benefit because
(frostbite) injury in both World Wars and in the Korean War, decreased metabolism lessens ischemic risk, so prehospital
documentation of this risk was eliminated from at least one caregivers are to thermally manage injured limbs. With both
1951 book. Although the author was a military surgeon who heating and cooling, limb management is to account for both
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discussed extreme cold weather and referenced a publication benefits and risks simultaneously while taking into consider-
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that reported that risk, the risk was absent from the book. 98 ation core temperature status. The temperature safety limits
and level of providers for such future guidelines are not yet
A 1968 military field manual on cold weather noted at the set. The concept of evaporative heat loss from fresh wound
end of a tourniquet paragraph: “Halting of circulation to surfaces or external hemorrhage in trauma may be important
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the extremities is an invitation to frostbite.” A 1970 com- in extreme cold weather, and it may be an awareness gap in
bat first-aid guideline for small, independent action forces in- need of a fill. Countermeasures to excessive cooling of limbs
cluded a note dealing with care after tourniquet application: may be developed as a list for potential instruction as either
“In extremely cold weather, protect any extremity with a tour- interventions or helping behaviors; these may be developed
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niquet applied to prevent cold injury.” This note explicitly into information scaled to match end-user ability in caregiv-
made thermal management of injured limbs a helping behavior ing. In casualties with cold limbs and first-aid tourniquets in
within first aid, although it was intended for enactment by use, tourniquet conversion may worsen core temperature de-
elite US Forces and not by the lay public. Also, as with other creases, and this may need specific research and development
resources, no example of how to enact thermal protection was for emergency caregiving. The effect size of this “afterdrop”
given. Frequency of advice about tourniquets risking cold in- caused by tourniquet conversion needs study to allow it to
jury decreased during and after the Vietnam War until such be stratified to different ambient temperatures and the num-
advice essentially ended after military reports in 2001. 101,102 bers of limbs with tourniquets used. If future investigators
One noted that, in treatment of a frozen limb to avoid further calculated the time (abscissa) difference between cooling rates
injury, use of a tourniquet should be avoided if, for example, a (temperature, ordinate) with and without tourniquet use to or
compress will suffice. Notably, while the Vietnam-era guid- below supercooling, then the effect size of hastening frostbite
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ance did explicitly note a tourniquet-frostbite association, the can be estimated, and such a finding could inform caregiving.
2001 guides did not; they noted only that the tourniquet adds
ischemic and compression trauma to the injured limb.
Conclusions
Although limb cooling risk is well established for tourni- The cause of frostbite is a sufficiently negative heat-transfer
quets used routinely in research experiments and clinical sur- trend in local tissues, and tourniquet use may exacerbate the
gery, 103–105 limb warming risk is also established, 106–110 albeit development of frostbite. Tourniquet-hastened frostbite exists
less known. During local cooling and heating in human limbs, as an association but not as cause and effect. Tourniquet use
the role of blood as heat source or heat sink is the principle un- increases the risk of the cold causing frostbite by allowing
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derlying these risks and their prevention. With a tourniquet faster and more reliable cooling. Such frostbite occurs in low
effect, excess heat transferred to the limb causes local heating frequency but at high severity because limb loss is a morbid
and risks heat injury 106–109 because blood cannot distribute the complication to be avoided. Care providers above the level of
heat load to the rest of the body. Likewise in a historical re- lay public are to be warned that first-aid tourniquet use risks
view of a research council, a researcher was reported to have frostbite when cold weather is below 0°C (32°F).
shown “that by occluding the circulation with a tourniquet,
the same depth of burn could be produced in one fifth the time Funding
it took with the circulation intact,” meaning that tourni- This project was funded by the US Army Medical Research
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quet-hastened burn occurred faster, perhaps in an experiment. and Development Command.
Such inability to off-load excess heat is clinically relevant to
rewarming cold limbs, such as by a fire, especially if the limb Disclaimer
has frostbite or a tourniquet in use. Also, for a casualty in a The views expressed in this article are those of the authors and
rewarming bag while a tourniquet is in use, a heating device do not reflect the official policy or position of the US Army
that is placed incorrectly or displaces from where it was put Medical Department, Department of the Army, Department of

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