Exertional heat stroke treatment in austere settings
30 Sep 2024
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Exertional heat stroke (EHS) is a critical and potentially life-threatening condition that occurs when intense physical activity leads to dangerously high body temperatures. Rapid recognition and treatment of EHS are essential, particularly in the austere environments faced by AUSMAT teams.
Dr Matt Brearley, a thermal physiologist affectionately known as 'the heat guy' within the AUSMAT community, supports AUSMAT teams before and during deployments through heat acclimatisation. Dr Brearley shares his insights into effective treatment strategies for EHS in austere environments. By focusing on practical solutions and the latest evidence, he aims to assist AUSMAT members in enhancing their response to this critical emergency. He explores the most effective methods for cooling EHS patients, comparing traditional approaches with newer techniques suited for field conditions. Whether dealing with high-intensity operations or remote deployments, Dr Brearley offers valuable guidance to ensure the best possible outcomes for those affected by heat stroke.
Exertional heat stroke (EHS) is a medical emergency defined as life-threatening hyperthermia (core body temperature exceeding 40°C) and central nervous system dysfunction, typically resulting from excessive physical exertion that overwhelms the body’s ability to regulate its temperature (Figure 1). Individuals engaged in strenuous activities, whether in occupational, sporting, military settings, or emergency response settings, are at increased risk of EHS. For AUSMAT members, the risk is heightened during deployments involving high tempo work in hot and humid conditions.
The severity and duration of EHS can be assessed by monitoring the patient’s core temperature and the area under their core temperature curve. Sustained hyperthemia increases the likelihood of Systematic Inflammatory Response Syndrome and organ failure. Therefore, effective EHS treatment focuses on rapidly lowering core temperature.
The critical treatment window for EHS is just 30 minutes, otherwise known as the ‘golden half hour’. Lowering core temperature to below 39°C within 30 minutes of EHS onset ensures survival and reduces the risk of long-term complications (Casa et al., 2015). For example, a study involving 454 EHS patients at a major endurance running event over 35 years, found that those with an average core temperature of 41.4°C and treated with approximately 10°C water immersion achieved a core temperature reduction of approximately 2.5°C within about 15 minutes (Stearns et al., 2024). All 454 EHS patients survived. 88% were discharged into the care of family members or friends while the remaining 12% were transported to emergency departments.
Traditionally, Australian recommendations for EHS treatment have focused on the application of ice packs or cold compresses to the shallow arteries of the neck, axillae and groin rather than water immersion (ANZCOR Guideline 9.3.4, 2016). However cooling rates with cold compresses are 5-10 times less effective when compared to water immersion, which can be insufficient for cooling EHS patients within the critical treatment window (Brearley, 2019). While cold water immersion remains the gold standard EHS treatment, the combination of limited access to cold water in austere settings and the challenges of managing an unconscious patient in water presents significant logistical and safety issues.
An alternative treatment that has shown effective cooling rates in field conditions is the use of cold, wet towels (ice towels) over the entire body (Table 1). The ice towel method is practical for austere environments, requiring only an ice box or esky, along with ice, water and cotton towels. Furthermore, it can be managed by an individual while awaiting medical support, offering a feasible solution when immediate water immersion isn’t available.
Table 1. Core temperature cooling rates for selected cooling modalities
Since the outcome from EHS is dependent upon the duration and severity of core temperature elevation, medical treatment seeks to minimise the area under the core temperature curve to ensure survival and prevent long-term medical complications. Returning core temperature to less than 39ºC within the 30-minute treatment window or 'golden half hour' post collapse is the objective. Based upon the evidence, rotation of ice towels over the entire body is an effective treatment, with reported cooling rates of 1.1ºC per 10 minutes (Table 1).
The Australian and New Zealand Committee on Resuscitation (ANZCOR) updated its guidelines in September 2020 to recommend: “Immerse (i.e. whole-body from the neck down) in cold water (a bath if possible, as cold as possible) for 15 minutes” (ANZCOR Guideline 9.3.4, 2020), reflecting the latest research. The guidelines also state: “If this is not available, a combination of the following methods should be used:
- Wet the person with cold or cool water, under a shower if safe, or with a hose or other water source
- Apply ice packs (groin, armpits, facial cheeks, palms and soles)
- Repeatedly moisten the skin with a moist cloth or atomizer spray
- Fan continuously.”
The ice towel method effectively wets the EHS patient with cold water and through rotation of the towels through cold water approximately every 2 minutes or as they warm.
Figure 2. Core temperature response to various cooling methods (oC)
Figure 3. An example of whole body cooling with ice towels (Hosokawa et al., 2021). Source: Hosokawa et al., 2021
In practice, EHS treatment kits equipped with ice boxes or eskies stocked with ice, water and several towels have been deployed to support heat-exposed workers. In some instances, medical support may reach an EHS patient after the gold half hour. Hence, the objective of the kits is to ensure EHS is appropriately treated while awaiting medical support. In March 2023, an EHS kit was used to rapidly cool a worker in North Queensland during the critical period before medical support arrived. According to the Queensland Ambulance Service paramedics, “If cooling had not been initiated when it was, the worker would have likely suffered irreversible damage or even death” (Rogerson and Brearley, 2024). The ice towel method was deemed cost effective, portable, scalable, and could be implemented by a single worker under the stress of an emergency.
Effective treatment of EHS is crucial for ensuring patient survival and minimising long-term effects. In austere settings, rapid and effective cooling strategies are essential to mitigate the risks of severe outcomes. By adhering to updated guidelines and adapting treatment methods to the constraints of field conditions, AUSMAT teams and other emergency responders can enhance their preparedness and response to EHS. This approach is particularly important where traditional methods, such as cold-water immersion, may be impractical. Ultimately these efforts help safeguard the health and safety of individuals in high-intensity and challenging environments.
References
ANZCOR Guideline 9.3.4 – Heat Induced Illness (Hyperthermia) 2016
ANZCOR Guideline 9.3.4 – Heat Induced Illness (Hyperthermia) 2020
Brearley M. Are Recommended Heat Stroke Treatments Adequate for Australian Workers? Annals of Work Exposures and Health. 2019, 63:263-266
Casa DJ, DeMartini JK, Bergeron MF, Csillan D, Eichner ER, Lopez RM, Ferrara MS, Miller KC, O'Connor F, Sawka MN, Yeargin SW. National Athletic Trainers' Association position statement: exertional heat illnesses. Journal of athletic training. 2015 Sep 1;50(9):986-1000.
Hosokawa Y, Racinais S, Akama T, Zideman D, Budgett R, Casa DJ, Bermon S, Grundstein AJ, Pitsiladis YP, Schobersberger W, Yamasawa F. Prehospital management of exertional heat stroke at sports Competitions: international Olympic Committee adverse weather impact expert Working group for the Olympic Games Tokyo 2020. British journal of sports medicine. 2021;55(24):1405-10.
Rogerson S, Brearley M. Suspected exertional heat stroke; A case study of worker cooling in a hot and humid field environment. Work. 2024, In press
Stearns RL, Hosokawa Y, Belval LN, Martin DG, Huggins RA, Jardine JF, Casa DJ. Exertional heat stroke survival at the Falmouth Road Race: 180 new cases with expanded analysis. Journal of athletic training. 2024 Mar 1;59(3):304-9.
