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Elite athletes competing at high-intensity in the hot and humid ambient conditions of the upcoming Games of the XXXII Olympiad (Tokyo 2020) are likely to reach elevated core temperature ( ≈ 41.5°C) as previously reported in elite competitions in the heat and the risk of exertional heat stroke (EHS) is heightened.1 EHS is a medical condition defined as an internal body temperature exceeding 40.5°C with central nervous system dysfunction (eg, disorientation, aggressiveness, hysteria, delirium, altered consciousness, irrational behaviour).2 3
Survival and sequela from EHS depend on the duration of hyperthermia.4 In 2020, evidence-based consensus suggests whole-body cooling until 39°C within the first 30 min of collapse as the critical requirement to maximise patient outcome.2 3 5 Whole-body cold water immersion (CWI) was associated with 100% survival rate in 274 runners diagnosed with EHS over the 18 years of patients treated at the New Balance Falmouth Road Race, with average cooling rate of 0.22°C min–1.5 In a different study, CWI using circulated water controlled at 2°C demonstrated an average cooling rate of 0.35°C min–1.6
To achieve the clinical target, medical providers at Tokyo 2020 must:
provide on-site assessment of internal body temperature using rectal thermometer,
provide whole-body CWI at the venue medical tent if it is needed,
be able to reduce internal body temperature below 39°C prior to hospital transport and
coordinate care by medical providers who are involved in EHS management on-site, during transport and at hospital.
Be able to assess
The first step of EHS management is assessment of internal body temperature.2 3 Currently, the only valid internal body temperature assessment method that can accurately diagnose EHS and practical in prehospital setting is rectal temperature (TREC).2 3 Other methods of temperature assessment (eg, tympanic, oral, axillary, temporal temperatures) have shown to be less reliable when used during or immediately after exercise and in outdoor condition.7 The ability to accurately assess body temperature is also important in determining the end point of EHS treatment (ie, cooling). While an aggressive whole-body cooling is warranted at the venue medical tent, medical providers must also take precautions to prevent patients from experiencing hypothermia—afterdrop.
Determining when to stop cooling
In most literature and recommendations, cooling rate is reported linearly, such as the recommended minimum cooling rate of 0.15°C min–1 for EHS treatment.2 However, in real-life observations of patients with EHS during cooling, it is evident that changes in TREC are non-linear and that there are variabilities in patient response. Figure 1 summarises TREC data of patients with EHS (n=14) treated at the 2016 New Balance Falmouth Road Race. The average cooling duration and rate were 13.5 min and 0.16°C min–1; however, the rate of cooling became faster in the latter 2/3 of the cooling (figure 1A), which is a trend that is commonly observed. In addition, the SD of cooling duration was 4.7 min, which shows a large variability in patient response (figure 1). Therefore, medical providers must use direct measurement of TREC to confirm reduction of internal body temperature below 39°C. Contrarily, there may be times when the patient presents with unreasonably fast cooling rate (figure 1B), which would require medical providers to question the value and reassess the temperature. In such circumstances, it is important for medical providers to acknowledge the average cooling curve and time as a reference to make comprehensive evaluation of the patient.
Managing patient after cooling
Once the cooling is completed, the patient in Tokyo should be removed from the ice bath and should have the TREC monitored for at least another 15 min. This is to ensure that the patient will regain their ability to thermoregulate and not experience afterdrop from whole-body CWI (figure 1C). Although the frequency of EHS cases with afterdrop is difficult to estimate, Tokyo 2020 medical providers should anticipate such cases and have a plan to the coordinate care on-site, during transport and at hospital. Venue medical guideline must explain when to transport the patient from one section to another and establish the EHS management sequence: (1) recognise (ie, transporting patient to medical tent), (2) assess (ie, taking TREC), (3) treat (ie, whole-body CWI and monitor TREC continuously), (4) monitor recovery (ie, continuous TREC monitoring), (5) transport (ie, discharging athlete from on-site medical tent and transporting to advanced care) and (6) follow-up examination (ie, physical examination at hospital).
While the basic principle of EHS management is simple (cool first, transport second), preparing for real-life scenario during an Olympic event required intensive practice by local medical providers and this will ensure that the roles of each medical provider are clearly defined.8 We recommended that medical directors of athletic events have a written manual to illustrate current best practice and that they conduct at least one face-to-face hands-on training session at assigned venues to go over the four key elements of EHS management.
Contributors All authors contributed to the conception of the work. YH contributed to the acquisition, analysis and interpretation of data presented in the manuscript. All authors contributed in drafting or revising the manuscript and approval of final version to be published.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests YH, DJC and SR have a potential COI as members of the IOC Adverse Weather Impact expert working Group for the Olympic Games Tokyo 2020; not receiving honorarium.
Patient consent for publication Not required.
Provenance and peer review Not commissioned; externally peer reviewed.
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