Page 14 - JSOM Spring 2023

Investigators have justified tourniquets to hasten frostbite to the translator meant that the distal limb was a body part and
mimic frozen digits of patients wearing constricting boots or did not mean that this heat loss was from the core. The time
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gloves at the time of cold injury. The varied ways to obstruct parameters tabularized appear to be in minutes and seconds;
limb circulation are clinically relevant because each risks faster if so, the tourniquet-hastened time differences are of the order
and worse cooling rates of tissue under and distal to the sites of 1 to 5 minutes at -34°C to -36°C (-29.2°F to -32.8°F) in a
of external compression. wind speed of 0.46 to 1.29m/sec.

In an animal experiment of deep frostbite in bone, researchers Clinical Guidance for Caregiving to
sought to decrease the variability in physiology resulting from Casualties at Risk for Frostbite With Tourniquet Use
known problems such as protective cold-induced vasodilation A US Army technical bulletin on cold injury estimates an on-
rewarming of the cooled limb and the supercooling phenom- set time to cheek-skin frostbite ranging on the order of 5 to
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enon, a process of cooling a liquid (e.g., extracellular fluid 30 minutes, depending on personnel susceptibility, severity of
in the skin or soft tissue) below the freezing point without temperature, windspeed, and whether the skin is wet. Beyond
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solidification. The time required to end supercooling was re- water, blood or sweat qualify as wetting. However, the bulletin
liably shorter with a tourniquet than without, and blocking does not mention tourniquets, although it mentions restric-
cold-induced vasodilation by tourniquet use seemed to hasten tive clothing, gloves, and facemasks, which can fit tightly and
and more reliably worsen the severity of frostbite. The inves- so restrict the blood flow to the fingers and face, increasing
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tigators inferred increased severity because they controlled the the susceptibility of these areas to frostbite; such restriction is
cold-exposure times so that durations of frostbite were longer analogous to a tourniquet effect on a limb. With the exception
when its onset was earlier, leading to worse lesions. Supercool- of contact frostbite, there is no risk of frostbite when the ambi-
ing has been noted as a normal phenomenon. 89,90 ent air temperature is above 0°C (32°F). Contact of a casualty
or tourniquet user to a cold metal component of a tourniquet,
Methods to investigate frostbite experimentally need to im- such as an aluminum rod used to tighten the band around the
prove the reliability of onset, speed of onset, and controlla- limb, may cause contact freezing promptly at the site where
bility of severity of the induced frostbite, thereby allowing the bare skin and metal touch, but to our knowledge, this phe-
more rigorous standardization and comparison across studies. nomenon has only been preliminarily studied in our labora-
It is important to make experimental frostbite severity more tory in unreported work on poultry groceries.
uniform and to reduce risks associated with anesthetic use.
Limited animal evidence indicates that tourniquet use worsens Böhler noted cases of tourniquet use with frostbite and judged
the development of frostbite. Altogether, such experimental that tourniquets had been selected too often or used too long
frostbite in animals does not closely mimic clinical frostbite in such cases, but he did not comment on tourniquet removal
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because frostbite in humans is often slower in onset, affected in the field or at the hospital. Conversion of tourniquets may
by clothing, and more varied in severity. However, limited ex- not be clinically feasible if field caregivers identify frostbite
perimental evidence derived from animals indicates that an distal to the tourniquet in a setting where they cannot ensure
association between tourniquet use and frostbite development that the thawed frostbite will not later refreeze. In practice,
exists, as Böhler noted. Although the risk of tourniquet- this is a difficult decision relying on prediction. Böhler noted
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hastened frostbite is rarely mentioned in first aid, the asso- that caregivers sometimes needlessly left the limb constricted
ciation is now more often described as a technique used in by use of a tourniquet during transport, with the implication
physiological experiments. Tellingly, we found no animal ex- that tourniquet conversion to other means of bleeding control
periment intended to inform prevention and control of clinical was possible. For a casualty with a tourniquet and a distal
tourniquet- hastened frostbite. site of frostbite, the volume of tissue distal to the tourniquet
and not already frozen is at higher risk to become frostbitten,
In a translated summarization of a Japanese human experi- thereby worsening the cold injury volume and likely losing
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ment, a text section, entitled “Obstruction of Blood Circu- more of the limb volume to complications requiring surgical
lation,” noted: amputation. Such a scenario complicates judging the clinical
conundrum of whether to rewarm distal frostbite in the field.
We have already noted that when the easily frozen ex-
tremities of the human body are cooled, the blood cir- Wolff and Adkins advised that care be used to prevent frost-
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culating in those parts supplies the heat required to bite in sub-freezing weather. Although they gave no example
counteract further cooling. Should this blood flow be ob- of such care, their advice implied that thermal management
structed in one way or another, the anti-cooling action is of injured limbs was useful to prevent frostbite. This intent is
weakened or ceases, and continued loss of heat will lead sound, but it presumes that a general reader knows what such
to the onset of freeze injury. In this connection, one may care would entail. Few people with whom we have discussed
recall that a wounded leg dressed with a tourniquet or a this tourniquet-hastened frostbite risk point were aware of its
foot in an undersized shoe is easily frozen. The influence risk or management, although they quickly grasped the risk as
of a tourniquet in inducing freeze injury can be seen from it was explained. Tourniquet hastened frostbite risk and ther-
Tables 25 and 26. Thus the use of a tourniquet doubles mal management of injured limbs remain awareness gaps in
the speed of body heat loss. We obtained this result from knowledge and capability.
experimentation with healthy persons. Needless to say,
in the case of a wounded limb, the loss of heat is further In both World Wars and in the Korean War, clinical advice
accelerated by bleeding. 91 occasionally noted that in cold weather, tourniquet use makes
a limb susceptible to freezing. 39,92–94 Two senior surgeons noted
The tourniquet halved the frostbite onset time, an experimen- that, while care was taken to prevent frostbite and other cold
tal effect in a clinically relevant size. The wording appears as if injuries in cold and freezing weather, it was the rule to leave

12 | JSOM Volume 23, Edition 1 / Spring 2023