Accidental hypothermia in recreational activities in the mountains: A narrative review

Emergency Care for High-Altitude Trekking and Climbing

van Veelen, Michiel J., Rudolf Likar, Markus Tannheimer, Konrad E. Bloch, Silvia Ulrich, Michael Philadelphy, Barbara Teuchner, Thomas Hochholzer, Jacqueline Pichler Hefti, Urs Hefti, Peter Paal, and Martin Burtsche. Emergency Care for High-Altitude Trekking and Climbing. High Alt Med Biol. 26:70-86, 2025. Introduction: High altitude regions are characterized by harsh conditions (environmental, rough terrain, natural hazards, and limited hygiene and health care), which all may contribute to the risk of accidents/emergencies when trekking or climbing. Exposure to hypoxia, cold, wind, and solar radiation are typical features of the high altitude environment. Emergencies in these remote areas place high demands on the diagnostic and treatment skills of doctors and first-aiders. The aim of this review is to give insights on providing the best possible care for victims of emergencies at high altitude. Methods: Authors provide clinical recommendations based on their real-world experience, complemented by appropriate recent studies and internationally reputable guidelines. Results and Discussion: This review covers most of the emergencies/health issues that can occur when trekking or during high altitude climbing, that is, high altitude illnesses and hypothermia, freezing cold injuries, accidents, for example, with severe injuries due to falling, cardiovascular and respiratory illnesses, abdominal, musculoskeletal, eye, dental, and skin issues. We give a summary of current recommendations for emergency care and pain relief in case of these various incidents.

Are Suggested Hiking Times Accurate? A Validation of Hiking Time Estimations for Preventive Measures in Mountains

Background and Objectives: Accurate hiking time estimate is crucial for outdoor activity planning, especially in mountainous terrains. Traditional mountain signage and online platforms provide generalized hiking time recommendations, often lacking personalization. This study aims to evaluate the variability in hiking time estimates from different methods and assess the potential of a novel algorithm, MOVE, to enhance accuracy and safety. Materials and Methods: A cross-sectional analysis was conducted using data from 25 Italian loop trails selected via the Wikiloc platform, considering user-uploaded GPS data from at least 20 users per trail. Real-world hiking times were compared with estimations from Komoot, Outdooractive, mountain signage, and the MOVE algorithm, which incorporates individualized biological and trail characteristics. Results: Significant discrepancies were observed between actual hiking times and estimates from Komoot (ΔWK: -48.92 ± 57.16 min), Outdooractive (ΔWO: -69.13 ± 58.23 min), and mountain signage (ΔWS: -29.59 ± 59.90 min; all p < 0.001). In contrast, MOVE showed no statistically significant difference (ΔWM: -0.27 ± 65.72 min; p = 0.278), providing the most accurate predictions. Conclusions: Current hiking time estimation methods show substantial variability and inaccuracy, which may pose safety risks. MOVE demonstrated superior accuracy, offering personalized hiking time predictions based on user-specific data and trail characteristics. Integrating such advanced tools into outdoor activity planning could enhance safety and accessibility, particularly for individuals with chronic conditions. Further studies should explore integrating real-time health data to refine these tools.

Clinical outcomes of challenging out-of-hospital hypothermia management: A retrospective assessment of DOKEI protocol

BACKGROUND

Accidental hypothermia (AH) is a major cause of death in mountainous areas globally, and the second highest of mountaineering deaths in Japan, accounting for 37 % in Hokkaido. Managing AH is a significant challenge, particularly when adverse weather complicates the application of recommended rewarming and rapid transfer. To address this, the Hokkaido Police Organization (DOKEI) AH protocol was applied in Hokkaido's remote areas from 2011 to 2022, integrating high-temperature active external rewarming (HT-AER) with on-site sustained treatment.

METHODS

This study retrospectively analyzed the rescue reports and hospital records of hypothermia patients treated postprotocol, excluding patients with cold exposure, undetectable vital signs at rescue, and inadequate documentation. Protocol adherence and outcomes-hypothermia stage, cardiocirculatory collapse, survival, and neurological status-were assessed.

RESULTS

Among the 60 protocol-treated patients (19-74 years, 85 % male), 14 had stage 2 hypothermia, and 3 had stage 3 hypothermia. HT-AER was applied in 96.7 % of the patients. A total of 98.3 % of patients improved before handover without cardiac arrest (CA) or extracorporeal life support (ECLS). Comparatively, ten preprotocol patients (18-60 years, 70 % male) had two CAs, one fatal and six with no improvement.

CONCLUSION

The DOKEI AH protocol demonstrates feasibility in managing stages 1-3 hypothermia, enhancing survival and neurological recovery, and can offer a vital option in challenging AH rescue scenarios.

Stretchable, flexible fabric heater based on carbon nanotubes and water polyurethane nanocomposites by wet spinning process

Wearable heaters are essential for people living in cold regions, but creating heaters that are low-cost, lightweight, and high air permeability poses challenges. In this study, we developed a wearable heater using carbon nanotube/water polyurethane (CNT/WPU) nanocomposite fibers that achieve high extension rate and conductivity. We produced low-cost and mass-produced fibers using the wet spinning. With heat treatment, we increased the elongation rate of the fibers to 1893.8% and decreased the resistivity to 0.07 Ω*m. then wove the fibers into a heating fabric using warp knitting, that resistance is 493 Ω. Achieved a uniform temperature of 58 °C at voltage of 36 V, with a thermal stability fluctuation of -5.0 °C to +6.3 °C when bent from 0° to 360°. Our results show that wearable heaters have excellent flexibility and stretchability, due to nanocomposite fibers and special braided structure, which offer a novel idea for wearable heaters.

Bioprotective role of platelet-derived microvesicles in hypothermia: Insight into the differential characteristics of peripheral and splenic platelets

BACKGROUND

Most platelets are present in peripheral blood, but some are stored in the spleen. Because the tissue environments of peripheral blood vessels and the spleen are quite distinct, the properties of platelets present in each may also differ. However, no studies have addressed this difference. We previously reported that hypothermia activates splenic platelets, but not peripheral blood platelets, whose biological significance remains unknown. In this study, we focused on platelet-derived microvesicles (PDMVs) and analyzed their biological significance connected to intrasplenic platelet activation during hypothermia.

METHODS

C57Bl/6 mice were placed in an environment of -20 °C, and their rectal temperature was decreased to 15 °C to model hypothermia. Platelets and skeletal muscle tissue were collected and analyzed for their interactions.

RESULTS

Transcriptomic changes between splenic and peripheral platelets were greater in hypothermic mice than in normal mice. Electron microscopy and real-time RT-PCR analysis revealed that platelets activated in the spleen by hypothermia internalized transcripts, encoding tissue repairing proteins, into PDMVs and released them into the plasma. Plasma microvesicles from hypothermic mice promoted wound healing in the mouse myoblast cell line C2C12. Skeletal muscles in hypothermic mice were damaged but recovered within 24 h after rewarming. However, splenectomy delayed recovery from skeletal muscle injury after the mice were rewarmed.

CONCLUSIONS

These results indicate that PDMVs released from activated platelets in the spleen play an important role in the repair of skeletal muscle damaged by hypothermia.

A numerical tool for assessing human thermal safety and thermal comfort in cold-weather activities

This paper describes a newly developed software tool to evaluate human thermal safety and thermal comfort in cold-weather activities aimed at guiding users to arrange activity plans and select appropriate clothing ensembles. The software inputs include conditions of activity, environment, human body, and clothing ensemble. It outputs physiological temperatures, cold injury risks, thermal sensations, and thermal comforts in intuitive ways like cloud maps and curves. The software tool is characterized by (1) integration of a thermoregulatory model that predicts human thermophysiological responses under exercise conditions in cold environments, (2) the functions of clothing ensemble database and individual parameter database, (3) the human centric outputs that directly reflect human physiological and mental status, and (4) the user-friendly operation interface and output interface, as well as a wide applicability. The software is validated with human test studies covering ambient temperatures from - 30.6 to 5 °C, clothing ensembles from 1.34 to 3.20 clo, and activity intensities from 2 to 9 Mets. The average prediction RMSEs of core temperature, mean skin temperature, thermal sensation, and thermal comfort are 0.16 °C, 0.45 °C, 0.58, and 1.41, respectively. The software is an advanced expansion to current standards and guidance of cold exposure assessment and a meaningful tool for the fields of occupational health care, cold protection, and environmental ergonomics.

Effects of low-intensity exercise on local skin and whole-body thermal sensation in hypothermic young males

Thermal sensation, a key component of behavioral thermoregulation, is modulated by the changes in both skin and core temperatures. Although cutaneous thermal sensation to local cold is blunted during exercise as compared to rest in normothermic humans, it remains to be determined whether this holds true during core cooling. Furthermore, when local skin thermal sensation is diminished during exercise, it remains unclear whether whole-body thermal sensation is also attenuated. We therefore tested whether low-intensity exercise (VO₂: ~1300 ml min^-1) attenuates local skin and/or whole-body thermal sensation in hypothermic young males. Eleven healthy young males (24 ± 2 years) were cooled through cold water immersion (18 °C) up to their lower abdomen while resting (rest trial) and during low-intensity cycling (30-60 W, 30 rpm) (exercise trial). Body temperature, cardiorespiratory variables, and whole-body (9-point scale: 0, unbearably cold; 4, neutral; 8, unbearably hot) and local skin thermal sensation were measured at baseline on land and before the esophageal temperature (T_es) began to decrease (defined as -0.0 T_es) and after 0.5 and 1.0 °C decrements in T_es from baseline during the immersion period. Local skin thermal sensation was measured using a thermostimulator with Peltier element that was attached to the chest. The temperature of the probe was initially equilibrated to the chest skin temperature, then gradually decreased at a constant rate (0.1 °C s ^-1) until the participants felt coolness. The difference between the initial skin temperature and the local skin temperature that felt cool was assessed as an index of local skin thermal sensation. Throughout the immersions, esophageal and mean skin temperatures did not differ between the rest and exercise trials. Local skin thermal sensation also did not differ between the two trials or at any core temperature level. By contrast, the whole-body thermal sensation score was higher (participants felt less cold) in the exercise than in the rest trial at esophageal temperature of -1.0 °C (1.25 ± 0.46 vs. 0.63 ± 0.35 units, P = 0.035). These results suggest that local skin thermal sensation during low-intensity exercise is not affected by a decrease in core temperature. However, whole-body thermal sensation mediated by a decrease in core temperature (-1.0 °C) is blunted by low-intensity exercise during cold water immersion.

Residual effects of short-term whole-body cold-water immersion on the cytokine profile, white blood cell count, and blood markers of stress

Background: One of the most challenging environmental extremes is immersion in cold/icy water, and consequent common assumption is that even a brief exposure to cold can lead to cold-related illnesses. The increase in the concentrations of the stress hormones cortisol, epinephrine (Epi), and norepinephrine (NE) in response to acute cold stress are thought to suppress the release of proinflammatory cytokines. No previous study has explored the residual consequences of whole-body short-term cold-water immersion (CWI; 14 °C for 10 min) on the immune response in healthy non-acclimated young adult men (aged 20-30 years).Materials and methods: In the current study, we tested the hypothesis that short-term acute whole-body CWI would induce high blood levels of cortisol, NE, and Epi, which in turn would increase circulating leukocyte numbers and delay the production of proinflammatory cytokines (tumor necrosis factor α (TNF-α), interleukin 1β (IL-1β), and IL-6). Results: Short-term whole-body CWI produced a stressful physiological reaction, as manifested by hyperventilation and increased muscle shivering, metabolic heat production, and heart rate. CWI also induced the marked release of the stress hormones Epi, NE, and cortisol. The change in IL-6 concentration after CWI was delayed and TNF-α production was decreased, but IL-1β was not affected within 48 h after CWI. A delayed increase in neutrophil percentage and decrease in lymphocyte percentage occurred after CWI.Conclusion: These findings suggest that, even though CWI caused changes in stress and immune markers, the participants showed no predisposition to symptoms of the common cold within 48 h after CWI.

Hypoxia gradually augments metabolic and thermoperceptual responsiveness to repeated whole-body cold stress in humans

New Findings

What is the central question of this study?

In male lowlanders, does hypoxia modulate thermoregulatory effector responses during repeated whole‐body cold stress encountered in a single day?

What is the main finding and its importance?

A ∼10 h sustained exposure to hypoxia appears to mediate a gradual upregulation of endogenous heat production, preventing the progressive hypothermic response prompted by serial cold stimuli. Also, hypoxia progressively degrades mood, and compounds the perceived thermal discomfort, and sensations of fatigue and coldness.

Abstract

We examined whether hypoxia would modulate thermoeffector responses during repeated cold stress encountered in a single day. Eleven men completed two ∼10 h sessions, while breathing, in normobaria, either normoxia or hypoxia (PO2: 12 kPa). During each session, subjects underwent sequentially three 120 min immersions to the chest in 20°C water (CWI), interspersed by 120 min rewarming. In normoxia, the final drop in rectal temperature (T_rec) was greater in the third (∼1.2°C) than in the first and second (∼0.9°C) CWIs (P < 0.05). The first hypoxic CWI augmented the T_rec fall (∼1.2°C; P = 0.002), but the drop in T_rec did not vary between the three hypoxic CWIs (P = 0.99). In normoxia, the metabolic heat production (M˙) was greater during the first half of the third CWI than during the corresponding part of the first CWI (P = 0.02); yet the difference was blunted during the second half of the CWIs (P = 0.89). In hypoxia, by contrast, the increase in M˙ was augmented by ∼25% throughout the third CWI (P < 0.01). Regardless of the breathing condition, the cold‐induced elevation in mean arterial pressure was blunted in the second and third CWI (P < 0.05). Hypoxia aggravated the sensation of coldness (P = 0.05) and thermal discomfort (P = 0.04) during the second half of the third CWI. The present findings therefore demonstrate that prolonged hypoxia mediates, in a gradual manner, metabolic and thermoperceptual sensitization to repeated cold stress.

Hearables: New Perspectives and Pitfalls of In-Ear Devices for Physiological Monitoring. A Scoping Review

Technological advancements are opening the possibility of prolonged monitoring of physiological parameters under daily-life conditions, with potential applications in sport science and medicine, and in extreme environments. Among emerging wearable technologies, in-ear devices or hearables possess technical advantages for long-term monitoring, such as non-invasivity, unobtrusivity, good fixing, and reduced motion artifacts, as well as physiological advantages related to the proximity of the ear to the body trunk and the shared vasculature between the ear and the brain. The present scoping review was aimed at identifying and synthesizing the available evidence on the use and performance of in-ear monitoring of physiological parameters, with focus on applications in sport science, sport medicine, occupational medicine, and extreme environment settings. Pubmed, Scopus, and Web of Science electronic databases were systematically searched to identify studies conducted in the last 10 years and addressing the measurement of three main physiological parameters (temperature, heart rate, and oxygen saturation) in healthy subjects. Thirty-nine studies were identified, 24 performing temperature measurement, 12 studies on heart/pulse rate, and three studies on oxygen saturation. The collected evidence supports the premise of in-ear sensors as an innovative and unobtrusive way for physiological monitoring during daily-life and physical activity, but further research and technological advancement are necessary to ameliorate measurement accuracy especially in more challenging scenarios.