Cold Injury.

Cold injury has been documented for centuries and remains a concern for military personnel, winter recreationalists, and urban homeless populations. Treatment advances in the last decades have included thrombolytic and prostaglandin therapies however the mainstay remains early recognition and rapid rewarming. This chapter focuses on frostbite, with a brief overview of other cold related conditions.

Elucidation of the Role of TRPV1, VEGF-A, TXA2, Redox Homeostasis, and Inflammatory Cascades in Protection against Cold Injuries by Herbosomal-Loaded PEG-Poloxamer Topical Formulation.

High-altitude regions, cold deserts, permafrost regions, and the polar region have some of the severest cold conditions on earth and pose immense perils of cold injuries to exposed individuals. Accidental and unintended exposures to severe cold, either unintentionally or due to occupational risks, can greatly increase the risk of serious conditions including hypothermia, trench foot, and cold injuries like frostbite. Cold-induced vasoconstriction and intracellular/intravascular ice crystal formation lead to hypoxic conditions at the cellular level. The condition is exacerbated in individuals having inadequate and proper covering and layering, particularly when large area of the body are exposed to extremely cold environments. There is a paucity of preventive and therapeutic pharmacological modalities that have been explored for managing and treating cold injuries. Given this, an efficient modality that can potentiate the healing of frostbite was investigated by studying various complex pathophysiological changes that occur during severe cold injuries. In the current research, we report the effectiveness and healing properties of a standardized formulation, i.e., a herbosomal-loaded PEG-poloxamer topical formulation (n-HPTF), on frostbite. The intricate mechanistic pathways modulated by the novel formulation have been elucidated by studying the pathophysiological sequelae that occur following severe cold exposures leading to frostbite. The results indicate that n-HPTF ameliorates the outcome of frostbite, as it activates positive sensory nerves widely distributed in the epidermis transient receptor potential vanilloid 1 (TRPV1), significantly (p < 0.05) upregulates cytokeratin-14, promotes angiogenesis (VEGF-A), prominently represses the expression of thromboxane formation (TXA2), and significantly (p < 0.05) restores levels of enzymatic (glutathione reductase, superoxide dismutase, and catalase) and nonenzymatic antioxidants (glutathione). Additionally, n-HPTF attenuates oxidative stress and the expression of inflammatory proteins PGF-2α, NFκB-p65, TNF-α, IL-6, IL-1ß, malondialdehyde (MDA), advanced oxidative protein products (AOPP), and protein carbonylation (PCO). Masson's Trichrome staining showed that n-HPTF stimulates cellular proliferation, and increases collagen fiber deposition, which significantly (p < 0.05) promotes the healing of frostbitten tissue, as compared to control. We conclude that protection against severe cold injuries by n-HPTF is mediated via modulation of pathways involving TRPV1, VEGF-A, TXA2, redox homeostasis, and inflammatory cascades. The study is likely to have widespread implications for the prophylaxis and management of moderate-to-severe frostbite conditions.

The freeze-avoiding mountain pine beetle (Dendroctonus ponderosae) survives prolonged exposure to stressful cold by mitigating ionoregulatory collapse.

Insect performance is linked to environmental temperature, and surviving through winter represents a key challenge for temperate, alpine and polar species. To overwinter, insects have adapted a range of strategies to become truly cold hardy. However, although the mechanisms underlying the ability to avoid or tolerate freezing have been well studied, little attention has been given to the challenge of maintaining ion homeostasis at frigid temperatures in these species, despite this limiting cold tolerance for insects susceptible to mild chilling. Here, we investigated how prolonged exposure to temperatures just above the supercooling point affects ion balance in freeze-avoidant mountain pine beetle (Dendroctonus ponderosae) larvae in autumn, mid-winter and spring, and related it to organismal recovery times and survival. Hemolymph ion balance was gradually disrupted during the first day of exposure, characterized by hyperkalemia and hyponatremia, after which a plateau was reached and maintained for the rest of the 7-day experiment. The degree of ionoregulatory collapse correlated strongly with recovery times, which followed a similar asymptotical progression. Mortality increased slightly during extensive cold exposures, where hemolymph K+ concentration was highest, and a sigmoidal relationship was found between survival and hyperkalemia. Thus, the cold tolerance of the freeze-avoiding larvae of D. ponderosae appears limited by the ability to prevent ionoregulatory collapse in a manner similar to that of chill-susceptible insects, albeit at much lower temperatures. Based on these results, we propose that a prerequisite for the evolution of insect freeze avoidance may be a convergent or ancestral ability to maintain ion homeostasis during extreme cold stress.

Prolonged critical avalanche burial for nearly 23 h with severe hypothermia and severe frostbite with good recovery: a case report.

BACKGROUND: Accidental hypothermia with severe frostbite is a rare combination of injuries with a high risk for long-term sequelae. There are widely accepted recommendations for the management of avalanche victims and for frostbite treatment, but no recommendation exists for the treatment of frostbite in severe hypothermic patients, specifically for the management of hypothermic avalanche victims presenting with frostbite. CASE PRESENTATION: We present a case of a previously healthy, 53-year-old male skier who was critically buried by an avalanche at 2300 m of altitude at an ambient temperature of - 8 °C for nearly 23 h. The victim was found with the right hand out of the snow and an air connection to outside. He was somnolent with Glasgow Coma Scale 11 (Eye 4, Verbal 2, Motor 5) and spontaneously breathing, in a severely hypothermic state with an initial core temperature of 23.1 °C and signs of cold injuries in all four extremities. After rescue and active external forced air rewarming in the intensive care unit, the clinical signs of first-degree frostbite on both feet and the left hand vanished, while third- to fourth-degree frostbite injuries became apparent on all fingers of the right hand. After reaching a core body temperature of approximately 36 °C, aggressive frostbite treatment was started with peripheral arterial catheter-directed thrombolysis with alteplase, intravenous iloprost, ibuprofen, dexamethasone and regional sympathicolysis with a right-sided continuous axillary block. After ten months, the patient had no tissue loss but needed neuropathic pain treatment with pregabalin. CONCLUSION: The combination of severe accidental hypothermia and severe frostbite is rare and challenging, as drug metabolism is unpredictable in a hypothermic patient and no recommendations for combined treatment exist. There is general agreement to give hypothermia treatment the priority and to begin frostbite treatment as early as possible after full rewarming of the patient. More evidence is needed to identify the optimal dosage and time point to initiate treatment of frostbite in severely hypothermic patients. This should be taken into consideration by future treatment recommendations.

Phalangeal microgeodic syndrome: case report of a young woman treated with pentoxifylline.

Phalangeal microgeodic syndrome (PMS) is a rare osteolytic disorder of unknown etiology that typically affects children up to 15 years old during colder months. Transient peripheral circulatory impairment probably underlines its pathogenesis. Conservative treatment with eviction of cold exposure is often successful. We report the case of a young woman presenting with joint pain in her feet, along with toe discoloration and redness, where a diagnosis of PMS was established based on magnetic resonance imaging findings and exclusion of other differential diagnostic entities. Pharmacological treatment was deemed necessary for symptomatic relief, but a trial of calcium channel blocker (CCB) was not tolerated by the patient. The patient was then started on pentoxifylline, with significant clinical improvement.

Frostbite treatment: a systematic review with meta-analyses.

INTRODUCTION: Our objective was to perform a systematic review of the outcomes of various frostbite treatments to determine which treatments are effective. We also planned to perform meta-analyses of the outcomes of individual treatments for which suitable data were available. MAIN BODY: We performed a systematic review and meta-analyses in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses. We searched PubMed, Cochrane Trials, and EMBase to identify primary references from January 1, 1900, to June 18, 2022. After eliminating duplicates, we screened abstracts to identify eligible studies containing information on treatment and outcomes of Grade 2 to 4 frostbite. We performed meta-analyses of groups of articles that provided sufficient data. We registered our review in the prospective registry of systematic reviews PROSPERO (Nr. 293,693). We identified 4,835 potentially relevant studies. We excluded 4,610 studies after abstract screening. We evaluated the full text of the remaining 225 studies, excluding 154. Ultimately, we included 71 articles with 978 cases of frostbite originating from 1 randomized controlled trial, 20 cohort studies and 51 case reports. We found wide variations in classifications of treatments and outcomes. The two meta-analyses we performed both found that patients treated with thrombolytics within 24 h had better outcomes than patients treated with other modalities. The one randomized controlled trial found that the prostacyclin analog iloprost was beneficial in severe frostbite if administered within 48 h. CONCLUSIONS: Iloprost and thrombolysis may be beneficial for treating frostbite. The effectiveness of other commonly used treatments has not been validated. More prospective data from clinical trials or an international registry may help to inform optimal treatment.

Management of multiple frostbite casualties at a burn center: San Antonio, Texas, 12-20 February 2021.

BACKGROUND: Frostbite is an insidious disease that normally affects people of cold climates. Winter Storm Uri, which occurred from February 12-20, 2021, created unique metrological conditions for Texas. It caused prolonged sub-freezing temperatures and led to rolling blackouts, affecting 2.8 million Texans including 300,000 people in San Antonio. We report 13 frostbite patients admitted to one burn center during this event. OBJECTIVE: We aimed to determine the at-risk population for frostbite, to categorize their injury severity, and to describe their treatment. A secondary aim was to describe the rehabilitation management of these patients. METHODS: This is a single-center retrospective study. Each patient's injuries were assessed by a topographical grading system. Comparisons were made among those who were admitted to the intensive care unit (ICU), admitted to the progressive care unit (PCU), and treated as outpatients. RESULTS: Thirteen patients were identified. Ten (76.9 %) considered themselves homeless, and 9 (69.2 %) were directly exposed to the elements. The median delay between time of injury and presentation to a medical facility was 3 days (IQR 1-6). Only 3 patients presented to a medical facility within 24 h. Six (46 %) sustained grade 2 injuries, 2 (15 %) sustained grade 3 injuries, and 5 (38%) sustained grade 4 injuries. Only one patient met criteria to receive tissue plasminogen activator (tPA), which was discontinued due to hematochezia. Patients admitted to the ICU, when compared to patients admitted to the ward, had a longer length of stay (median 73 days v. 12 days, p = 0.0215), and required more amputations at below-the-knee or higher levels (3 v. 0, p-value 0.0442). CONCLUSION: In a region unaccustomed and perhaps unprepared to deal with winter storms, the population is particularly vulnerable to frostbite. Lack of awareness of frostbite injuries likely led to the delay in the presentation of patients, which prevented the timely use of tPA. Increasing public awareness may increase readiness.

Performance of a Chemical Heat Blanket in Dry, Damp, and Wet Conditions Inside a Mountain Rescue Hypothermia Wrap.

INTRODUCTION: Casualties with accidental hypothermia are evacuated using multilayer wraps, typically including a chemical heat blanket (CHB), a vapor barrier, and an insulating outer bag. We investigated CHB performance against dry, damp, and wet fabric, in a multilayer wrap, in response to a case report indicating diminished performance when wet. METHODS: We wrapped a torso manikin in a base layer, CHB, vapor barrier, casualty bag, and vacuum mattress, recording CHB panel temperatures at intervals of up to 7 h. Experimental conditions were dry, damp, and wet clothing, with 2 blankets tested in each condition. We subsequently used a forward-looking infrared camera to assess whether the panels heated evenly and heat flux sensors to quantify heat transfer across 2 dry, 1 damp, and 1 wet fleece under CHB panels. RESULTS: Chemical heat blankets maintained heat output for >7 h inside the wraps. Median (IQR) panel steady state temperatures were 52°C (39-56°C) against dry fleece, 41°C (36-45°C) against damp fleece, and 30°C (29-33°C) against wet fleece. Peak panel temperature was 67°C. The heat flux results indicated that CHBs generated similar quantities of heat in dry and damp conditions, as the lower temperatures were compensated by more efficient transfer of heat across the moist clothing layer. Chemical heat blanket heat output was diminished in wet conditions. CONCLUSIONS: Rescuers should cut off saturated clothing in a protected environment before wrapping casualties, but damp clothing need not be removed. Because of the high peak temperatures recorded on the surfaces of CHBs, they should not be placed directly against skin, and compression straps should not be placed directly over CHBs.

Prevalence of hypothermia and critical hand temperatures during military cold water immersion training.

Cold-weather military operations can quickly undermine warfighter readiness and performance. Specifically, accidental cold-water immersion (CWI) contributes to rapid body heat loss and impaired motor function. This study evaluated the prevalence of hypothermia and critical hand temperatures during CWI. One-hundred seventeen (N = 117) military personnel (mean ± SD age: 27 ± 6 yr, height: 176 ± 8 cm, weight: 81.5 ± 11.6 kg) completed CWI and rewarming during cold-weather training, which included a 10-min outdoor CWI (1.3 ± 1.4°C) combined with cold air (-4.2 ± 8.5°C) exposure. Following CWI, students removed wet clothing, donned dry clothing, and entered sleeping systems. Core (Tc) and hand (Thand) temperatures were recorded continuously during the training exercise. Tc for 96 students (mean ± SD lowest Tc = 35.6 ± 0.9°C) revealed that 24 students (25%) experienced Tc below 35.0°C. All of 110 students (100%) experienced Thand below 15.0°C, with 71 students (65%) experiencing Thand at or below 8.0°C. Loss of hand function and hypothermia should be anticipated in warfighters who experience CWI in field settings. Given the high prevalence of low Thand, focus should be directed on quickly rewarming hands to recover function.

Introduction: Training is more important than technology (for performance in the cold).

After more than 50 years of studying soldiers in the cold, we are well past the phase of defining the unique problems; the research requirements are known but the solutions have been slow in coming. This requires iterative testing of proposed lab-based solutions with soldiers in the real environment. Representing a renewed effort to produce and implement solutions to human biomedical challenges in Arctic operations, this journal supplement highlights presentations from a three-day NATO Human Factors and Medicine panel-sponsored symposium in Washington DC in October 2022. While technology can certainly aid soldiers in extreme environments, it is ultimately training that is the most important factor for ensuring optimal performance and survival. By investing in the development of specialized Arctic forces training and implementing new solutions to protect their health and performance, we can ensure success in the coldest and harshest of environments.

Freezing cold injuries among soldiers in the Norwegian Armed Forces - A cross sectional study.

INTRODUCTION: Freezing cold injuries (FCI) are a common risk in extreme cold weather warfare operations. The Norwegian Armed Forces (NAF) have the expertise and capabilities in education and training for warfighting capabilities in the Arctic. Nevertheless, a substantial number of Norwegian soldiers sustain freezing cold injuries annually. The aim of this study was to describe the FCI in the NAF, the associated risk factors and clinical associations. METHODOLOGY: The subjects for the study were soldiers registered with FCI in the Norwegian Armed Forces Health Registry (NAFHR) between January 1st 2004-July1st 2021. The soldiers answered a questionnaire regarding background, activities at the time of injury, description of the FCI, risk factors, medical treatment and any sequelae from their FCI. RESULTS: FCI in the NAF were most frequently reported among young conscripts (mean20.5 years). Hands and feet are most often injured (90.9%). Only a minority (10.4%) received medical treatment. The majority (72.2%) report sequelae. Extreme weather conditions was the most important risk factor (62.5%). CONCLUSIONS: Most soldiers had the knowledge to avoid FCI, but they were injured anyway. It is concerning that only one in 10 injured soldiers received medical treatment after diagnosed with FCI, increasing the risk of FCI sequelae.

Can iloprost be used for treatment of cold weather injury at the point of wounding in a forward operating environment? A literature review.

INTRODUCTION: Cold Weather Injury (CWI) represents a spectrum of pathology, the two main divisions being Freezing Cold Injury (FCI) and Non-Freezing Cold Injury (NFCI). Both are disabling conditions associated with microvascular and nerve injury often treated hours after initial insult when presenting to a healthcarestablishment. Given that iloprost is used for the treatment of FCI, could it be used in a forward operating environment to mitigate treatment delay? Is there a role for its use in the forward treatment of NFCI? This review sought to evaluate the strength of evidence for the potential use of iloprost in a forward operating environment. METHODS: Literature searches were undertaken using the following question for both FCI and NFCI: in [patients with FCI/NFCI] does [the use of iloprost] compared to [standard care] reduce the incidence of [long-term complications]. Medline, CINAHL and EMBASE databases were searched using the above question and relevant alternative terminology. Abstracts were reviewed before full articles were requested. RESULTS: The FCI search yielded 17 articles that were found to refer to the use of iloprost and FCI. Of the 17, one referred to pre-hospital treatment of frostbite at K2 base camp; however, this was utilising tPA. No articles referred to pre-hospital use in either FCI or NFCI. DISCUSSION: Although evidence exists to support the use of iloprost in the treatment of FCI, its use to date has been in hospital. A common theme is delayed treatment due to the challenges of evacuating casualties from a remote location. There may be a role for iloprost in the treatment of FCI; however, further study is required to better understand the risk of its use.

A preliminary study of the thermal strain experienced by dive support boat personnel.

Anecdotal evidence indicated some British military dive support boat personnel suffer from uncomfortably cold hands and feet, which could impair their performance and be associated with reductions in core body temperature. This study collected preliminary data on thermal stress and cognitive performance of personnel taking part in a cold-weather training exercise. Six men were monitored during four boat transits in a range of climatic conditions (air temperature +1.2°C to -10.5°C, wind chill -4.5°C to 19.3°C). Core body temperature was measured with a radio pill and 12 skin sites (ISO 9886 plus hand, finger, foot and toe) with iButtons or thermistors. Self-reported thermal comfort and thermal sensation was also recorded. Reaction time and selective attention were measured pre- and post-transit. Participants' physical characteristics and personal clothing ensembles were recorded. No participant became hypothermic. Most participants' hand, foot and digit temperatures fell to below 15°C, indicating a risk of impaired dexterity, in addition to that arising from gloves. During the trial, hand and digit temperatures occasionally fell below 10°C. The limited data collected showed personal clothing choices could provide adequate thermal protection for these conditions and temperatures, and highlighted inter-individual variation and the need to allow for significant variation of day-to-day environmental conditions.

The classification of freezing cold injuries - a NATO research task group position paper.

INTRODUCTION: Freezing cold injuries (FCI) are a common risk in extreme cold weather operations. Although the risks have long been recognised, injury occurrences tend to be sparse and geographically distributed, with relatively few cases to study in a systematic way. The first challenge to improve FCI medical management is to develop a common nomenclature for FCI classification. This is critical for the development of meaningful epidemiological reports on the magnitude and severity of FCI, for the standardisation of patient inclusion criteria for treatment studies, and for the development of clinical diagnosis and treatment algorithms. METHODOLOGY: A scoping review of the literature using PubMed and cross-checked with Google Scholar, using search terms related to freezing cold injury and frostbite, highlighted a paucity of published clinical papers and little agreement on classification schemes. RESULTS: A total of 74 papers were identified, and 28 were included in the review. Published reports and studies can be generally grouped into four different classification schemes that are based on (1) injury morphology; (2) signs and symptoms; (3) pathophysiology; and (4) clinical outcome. The nomenclature in the different classification systems is not coherent and the discrete classification limits are not evidence based. CONCLUSIONS: All the classification systems are necessary and relevant to FCI medical management for sustainment of soldier health and performance in cold weather operations and winter warfare. Future FCI reports should clearly characterise the nature of the FCI into existing classification schemes for surveillance (morphology, symptoms, and appearance), identifying risk-factors, clinical guidelines, and agreed inclusion/exclusion criteria for a future treatment trial.

Development of interactive guidance for cold exposure using a thermoregulatory model.

For decades, the Wind Chill Temperature Index (WCT) and its various iterations have been used to assess the risk of frostbite on unclothed body parts. This paper presents an innovative knowledge-based Cold Weather Ensemble Decision Aid (CoWEDA) that can be used to guide the selection of the most appropriate cold weather ensemble(s) relative to anticipated mission physical activities and environmental conditions. CoWEDA consists of a validated six-cylinder thermoregulatory model, a database of clothing properties, algorithms for calculating the whole ensemble properties from individual garments and a graphical user interface. The user-friendly CoWEDA allows users to select from an inventory of clothing items to build an ensemble suitable for their needs. CoWEDA predicts the risks of both frostbite and hypothermia and ensures that a selected clothing ensemble will provide adequate protection to prevent cold injury. CoWEDA predictions provide not only estimates of frostbite risk similar to WCT tables but also hypothermia times and clothing required to prevent cold injuries. In addition, a CoWEDA model variant can predict survivability and clothing requirements during cold water immersion. Thus, CoWEDA represents a significant enhancement of the WCT-based guidance for cold weather safety and survival by providing greater individual fidelity in cold injury predictions.

Botulinum Toxin A in the treatment of frostbite sequelae - results from a blinded, early-phase, comparative trial.

INTRODUCTION: Freezing Cold Injuries (FCI) have been associated with long-term sequelae including vasospasm. The aims of the pilot study are to explore the research methodology and investigate the tolerability and safety of treatment with Botulinum Toxin-A (BTX-A) in FCI Sequelae. METHODOLOGY: This pilot study tests the logistics, the treatment setting and the follow-up procedure in an early-phase, double-blinded, randomized, controlled trial study-design. The variables in the study were subjective symptoms, peripheral micro-vascularization/rewarming, somatosensory responsiveness, and generic measure of health status. RESULTS: No major challenges or difficulties were noticed according to the protocol or the study methodology. The monitoring of tolerability and safety of treatment with BTX-A did not reveal any major unwanted and/or adverse reactions among the patients in the pilot study and no challenges occurred during data collection of endpoints. The study revealed an inaccuracy of the 2nd degree FCI diagnosis and uncover a need for relevant and sufficient clinical information for FCI classification. CONCLUSIONS: This pilot study showed the study methodology with minor adjustments is feasible in a future full-scale clinical trial. The recruitment process needs to be more refined to ensure that the eligible study participants are a homogenous group of FCI patients.

Extremity cooling during an arctic diving training exercise.

A field study was conducted to examine the vulnerability of military divers to non-freezing cold injury (NFCI) during Arctic ice-diving operations. Participants were instrumented with temperature sensors on the back of their hands and on the bottom of their big toe for each dive to measure cooling of their extremities. While NFCI was not diagnosed in any of the participants during this field study, the data indicate that the feet were particularly vulnerable during the dives given that they were mostly in a temperature zone that could cause pain and performance decrements. The data also show that for short term dives, the dry and wet suits with wet gloves in both configurations were thermally more comfortable for the hands than the dry suit with dry glove configuration; however, the latter would be more protective against potential NFCI during longer dives. Features such as hydrostatic pressure and repetitive diving that are unique to diving but not previously considered as risk factors for NFCI are examined herein and warrant deeper investigation given that symptoms of NFCI might be mistaken as decompression sickness.

Iloprost for the treatment of frostbite: a scoping review.

We performed a scoping review to identify the extent of the literature describing the use of iloprost in the treatment of frostbite. Iloprost is a stable synthetic analog of prostaglandin I2. As a potent inhibitor of platelet aggregation and vasodilator, it has been used to address the post-rewarming reperfusion injury in frostbite. The search using iloprost and frostbite as key words and MeSH terms yielded 200 articles. We included in our review the literature examining iloprost for the treatment of frostbite in humans in the form of primary research, conference proceedings and abstracts. Twenty studies published from 1994 to 2022 were selected for analysis. The majority were retrospective case series consisting of a homogeneous population of mountain sport enthusiasts. A total of 254 patients and over 1000 frostbitten digits were included among the 20 studies. The larger case series demonstrated a decrease in amputation rates relative to untreated patients. Primary gaps in the literature include a paucity of randomised trials and relatively limited study populations to date. While the case evidence is promising, a multi-centre collaboration would be crucial to adequately power prospective randomised studies to definitively determine if iloprost has a role in the treatment of frostbite.

Warning: Tourniquets Risk Frostbite in Cold Weather.

We sought to better understand the frostbite risk during first-aid tourniquet use by reviewing information relevant to an association between tourniquet use and frostbite. However, there is little information concerning this subject, which may be of increasing importance because future conflicts against near-peer competitors may involve extreme cold weather environments. Historically, clinical frostbite cases with tourniquet use occurred in low frequency but in high severity when leading to limb amputation. The physiologic response of vasoconstriction to cold exposure leads to limb cooling and causes a reduction of limb blood flow, but cold-induced vasodilation ensues as periodic fluctuations that increase blood flow to hands and feet. In animal experiments, tourniquet use increased the development of frostbite. Evidence from human experiments also supports an association between tourniquet use and frostbite. Clinical guidance for caregiving to casualties at risk for frostbite with tourniquet use had previously been provided but slowly and progressively dropped out of documents. Conclusions: The cause of frostbite was deduced to be a sufficiently negative heat-transfer trend in local tissues, which tourniquet use may worsen because of decreasing tissue perfusion. An association between tourniquet use and frostbite exists but not as cause and effect. Tourniquet use increased the risk of the cold causing frostbite by allowing faster cooling of a limb because of reduced blood flow and lack of cold-induced vasodilation. Care providers above the level of the lay public are warned that first-aid tourniquet use in low-temperature (<0°C [<32°F]) environmental conditions risks frostbite.