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.

We are all exposed, but some are more exposed than others.

This paper defines functional cold exposure zones that illustrate whether a person is at risk of developing physical performance loss or cold weather injuries. Individual variation in body characteristics, activity level, clothing and protective equipment all contribute to variation in the effective exposure. Nevertheless, with the right education, training, and cold-adapted behaviours the exposure differences might not necessarily lead to increased risk for cold injury. To support the preparation process for cold weather operations, this paper presents a biophysical analysis explaining how much cold exposure risk can vary between individuals in the same environment. The results suggest that smaller persons are prone to be underdressed for moderate activity levels and larger persons are prone to be overdressed. The consequences of these discrepancies place people at different risks for performance loss or cold weather injuries. Nonetheless, even if all are well-dressed at the whole-body level, variation in hand morphology is also expected to influence hand skin temperatures that can be maintained; with smaller hands being more prone to reach skin temperatures associated with dexterity loss or cold weather injuries. In conclusion, this work focusses on bringing cold science to the Arctic warrior, establishing that combating cold stress is not a one size fits all approach.

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.

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.

Human vulnerability and variability in the cold: Establishing individual risks for cold weather injuries.

Human tolerance to cold environments is extremely limited and responses between individuals is highly variable. Such physiological and morphological predispositions place them at high risk of developing cold weather injuries [CWI; including hypothermia and/or non-freezing (NFCI) and freezing cold injuries (FCI)]. The present manuscript highlights current knowledge on the vulnerability and variability of human cold responses and associated risks of developing CWI. This review 1) defines and categorizes cold stress and CWI, 2) presents cold defense mechanisms including biological adaptations, acute responses and acclimatization/acclimation and, 3) proposes mitigation strategies for CWI. This body of evidence clearly indicates that all humans are at risk of developing CWI without adequate knowledge and protective equipment. In addition, we show that while body mass plays a key role in mitigating risks of hypothermia between individuals and populations, NFCI and FCI depend mainly on changes in peripheral blood flow and associated decrease in skin temperature. Clearly, understanding the large interindividual variability in morphology, insulation, and metabolism is essential to reduce potential risks for CWI between and within populations.

Human performance research for military operations in extreme cold environments.

OBJECTIVES: Soldier performance in the Arctic depends on planning and training, protective equipment, and human physiological limits. The purpose of this review was to highlight the span of current research on enhancing soldier effectiveness in extreme cold and austere environments. METHODS: The practices of seasoned soldiers who train in the Arctic and cold-dwelling natives inform performance strategies. We provide examples of research and technology that build on these concepts. RESULTS: Examples of current performance research include evaluation of equipment and tactics such as the bioenergetics of load carriage over snow in Norwegian exercises; Canadian field monitoring of hand temperatures and freezing cold injuries for better protection of manual dexterity; and Dutch predictive modeling of cold-wet work tolerances. Healthy young men can respond to cold with a substantial thermogenic response based on US and Canadian studies on brown adipose tissue and other mechanisms of non-shivering thermogenesis; the potential advantage of greater fat insulation is offset in obese unfit subjects by a smaller thermogenic response. Current physiological studies are addressing previously unanswered problems of cold acclimation procedures, thermogenic enhancement and regulation, and modulation of sympathetic activation, all of which may further enhance cold survival and expand the performance envelope. CONCLUSION: There is an inseparable behavioral component to soldier performance in the Arctic, and even the best equipment does not benefit soldiers who have not trained in the actual environment. Training inexperienced soldiers to performance limits may be helped with personal monitoring technologies and predictive models.

Evaluating the Tactical Combat Casualty Care principles in civilian and military settings: systematic review, knowledge gap analysis and recommendations for future research.

OBJECTIVES: The Tactical Combat Casualty Care (TCCC) guidelines detail resuscitation practices in prehospital and austere environments. We sought to review the content and quality of the current TCCC and civilian prehospital literature and characterize knowledge gaps to offer recommendations for future research. METHODS: MEDLINE, EMBASE, CINAHL, and Cochrane Central Register of Controlled Trials were searched for studies assessing intervention techniques and devices used in civilian and military prehospital settings that could be applied to TCCC guidelines. Screening and data extraction were performed according to PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. Quality appraisal was conducted using appropriate tools. RESULTS: Ninety-two percent (n=57) of studies were observational. Most randomized trials had low risk of bias, whereas observational studies had higher risk of bias. Interventions of massive hemorrhage control (n=17) were wound dressings and tourniquets, suggesting effective hemodynamic control. Airway management interventions (n=7) had high success rates with improved outcomes. Interventions of respiratory management (n=12) reported low success with needle decompression. Studies assessing circulation (n=18) had higher quality of evidence and suggested improved outcomes with component hemostatic therapy. Hypothermia prevention interventions (n=2) were generally effective. Other studies identified assessed the use of extended focused assessment with sonography in trauma (n=3) and mixed interventions (n=2). CONCLUSIONS: The evidence was largely non-randomized with heterogeneous populations, interventions, and outcomes, precluding robust conclusions in most subjects addressed in the review. Knowledge gaps identified included the use of blood products and concentrate of clotting factors in the prehospital setting. LEVEL OF EVIDENCE: Systematic review, level III.

Energy Balance of Canadian Armed Forces Personnel during an Arctic-Like Field Training Exercise.

Operating in temperature extremes frequently leads to a discrepancy in energy balance. Investigating the effects of operating in extreme cold temperatures on metabolic requirements has not been well described in Canadian Armed Forces (CAF) personnel. The objective was to accurately assess energy deficits using the "gold standard" methodology for measuring energy intake (EI) and energy expenditure (EE). Nutritional intake of a convenience sample of 10 CAF Class A Reservists, completing a basic military qualification (land) course under winter weather conditions, was assessed using the daily measured food intake/food waste collections. EE was measured by the doubly-labelled water method. Average EI was 2377 ± 1144 kcal/day, which was below the EE (4917 ± 693 kcal/day), despite having ~5685 kcal available in the field rations. A significant body weight loss of 2.7% was associated with the average daily energy deficit of 2539 ± 1396 kcal. As a result, participants demonstrated voluntary anorexia. Such results may have important implications for the impairment of performance and health under longer duration operations.

Finger cold-induced vasodilation test does not predict subsequent cold injuries: A lesson from the 2018 Canadian Forces Exercise.

A cold-induced vasodilation (CIVD) test was administered to 113 Canadian Armed Forces (CAF) soldiers (age 25.6 ± 6 yrs) during pre-deployment to a Canadian Arctic training exercise. The incidence and rates/types of subsequent peripheral cold injuries, as well as the relationship of CIVD responses against other hypothesized/reported risk factors (smoking, gender, age, ethnicity and prior cold injury), were analyzed. Although there was a wide range of CIVD RIF (resistance index to frostbite) scores (mean = 5.0 ± 1.5), there were no systematic relationships between RIF and injury type/location and rate, and the other risk factors analyzed. The absence of physiological links to cold injury occurrence suggests that in a military cold deployment setting, other factors are in play, which might include clothing, training, leadership and doctrine. These factors should be examined in future work.

Medical Encounters During a Joint Canadian/U.S. Exercise in the High Arctic (Exercise Arctic Ram).

The Arctic Ram Exercise was conducted in February 2016, near Resolute Bay on Cornwallis Island in Nunavut, Canada, to demonstrate the ability of the Canadian Armed Forces (CAF) to rapidly deploy to the arctic as an immediate response team. This report describes medical problems experienced by the 187 CAF and 28 U.S. forces involved in the exercise. Sixty-six airborne soldiers performed tactical static line jumps and linked up with soldiers on the ground for the exercise. Medical events were recorded by medics on the drop zone and by medical personnel at the Unit Medical Station in Resolute Bay. Average temperature during the exercise was -21°C and wind chill was -44°C. Two U.S. soldiers were injured in association with the jump and an additional 62 patients presented at the clinic during the exercise for an overall medical event incidence of 30%. The incidence of frostbite was 17%. At the end of the exercise, a physician actively examined CAF soldiers in one unit (n = 126) and found that 21% had experienced frostbite. The incidence of frostbite was high in this exercise compared to past cold-weather military operations, likely related to the very low temperatures and wind chills.

A comparison of live tissue training and high-fidelity patient simulator: A pilot study in battlefield trauma training.

BACKGROUND: Trauma procedural and management skills are often learned on live tissue. However, there is increasing pressure to use simulators because their fidelity improves and as ethical concerns increase. We randomized military medical technicians (medics) to training on either simulators or live tissue to learn combat casualty care skills to determine if the choice of modality was associated with differences in skill uptake. METHODS: Twenty medics were randomized to trauma training using either simulators or live tissue. Medics were trained to perform five combat casualty care tasks (surgical airway, needle decompression, tourniquet application, wound packing, and intraosseous line insertion). We measured skill uptake using a structured assessment tool. The medics also completed exit questionnaires and interviews to determine which modality they preferred. RESULTS: We found no difference between groups trained with live tissue versus simulators in how they completed each combat casualty care skill. However, we did find that the modality of assessment affected the assessment score. Finally, we found that medics preferred trauma training on live tissue because of the fidelity of tissue handling in live tissue models. However, they also felt that training on simulators also provided additional training value. CONCLUSION: We found no difference in performance between medics trained on simulators versus live tissue models. Even so, medics preferred live tissue training over simulation. However, more studies are required, and future studies need to address the measurement bias of measuring outcomes in the same model on which the study participants are trained. LEVEL OF EVIDENCE: Therapeutic/care management study, level II.