Exertional Heat Stroke

Position Statement

The Faculty of Sport and Exercise Medicine (FSEM) UK has produced a guide for the immediate recognition and treatment of exertional heatstroke (EHS). EHS is a potentially fatal hyperthermia that occurs in exercising individuals, characterised by central neurological dysfunction and a markedly elevated core temperature (above 40.5°C). There is a significant risk of short- and long-term complications, particularly if there are delays in recognition and treatment. Rapid recognition and urgent treatment is therefore a priority.

Assessment of risk

1. It is vital that athletes, medical staff, and event organisers are aware of the potential risks of developing EHS during exercise, as well as the risk factors which may increase the likelihood of developing the condition. EHS is more common in warm and humid conditions with low wind speeds, where evaporation of sweat is a less effective mechanism for cooling. EHS may also occur in cooler conditions, however, where factors such as clothing and protective garments and the intensity of exercise may contribute. Vigilance is therefore required even in conditions of apparent low climatic stress. A wet-bulb globe temperature (WBGT) estimates the effect of temperature, humidity and solar radiation, and, if available, its use is recommended in assessing the risk of EHS.

Diagnosis

2. The diagnosis of EHS should be considered in any collapsed athlete, especially if there are signs of central nervous system (CNS) dysfunction (for example, confusion, irritability or acting out of character). A diagnosis of EHS can be made if these CNS signs are accompanied by a reliable measurement of a core temperature indicating hyperthermia (greater than 40.5°C). Medical staff should be aware that EHS may present with paradoxical signs of shivering and cool peripheries with poor perfusion. A rectal temperature is the recommended core temperature measurement in the field, and should be obtained in any collapsed or confused athlete where CNS recovery does not occur promptly with the cessation of exercise; peripheral methods of temperature measurement, including aural thermometers, may give false negative or erroneous readings.

Exertional heat illness (EHI) is a spectrum of heat disorders which includes EHS, but can occur at lower temperatures. If the history and presentation are compatible with a diagnosis of EHS, but rectal temperature measurement is not possible, delayed, or raised but below 40.5°C, then empiric treatment should be strongly considered.

Treatment

3. Heat stroke is a medical emergency and rapid onsite cooling intervention is required. Cold or ice-water immersion (CWI) is the most effective method of cooling a hyperthermic patient [1], which requires advance planning of the necessary resources and manpower.

If CWI is not available or practical (for example, if the athlete is agitated, or procedures need to be performed), then an alternative method is to spray the athlete with atomised water or wrap the athlete in wet towels whilst continuously fanning. Both methods are effective, by generating large heat losses; simultaneous fanning is recommended to enhance convective losses.

Immersing the athlete’s hands and feet in cool water can also be used as an adjunct. Ice packs provide some cooling, and are useful when combined with another method, but are less effective in isolation than the above methods. Cool IV fluids may also be beneficial, if available and appropriate to be given.

Commercially produced cooling jackets are available. Research into their efficacy is ongoing.

4. Athletes may be critically unwell with cardiorespiratory failure and severe neurological disturbance (for example, agitation, seizures, or a reduced level of consciousness) and may require emergent, life-saving treatment. Active cooling should take place concurrent with the life-saving treatment, or be started as soon as possible thereafter.

5. The aim of treatment is to reduce further metabolic heat production as quickly as possible and prevent organ damage. Targets for treatment should be a resolution of confusion and a core temperature below 38.5-39°C [2]. There is a risk of developing hypothermia during active cooling, and this may cause further metabolic heat production through the onset of shivering. Regular core temperature monitoring (for example, with an indwelling thermistor) is therefore important.

6. Unless patients fully recover rapidly after onsite cooling, they should be transferred to hospital. The decision to discharge without hospital assessment should be based on return to normothermia, normal neurocognitive function, and normal physical and biochemical parameters. Transfer to hospital should occur while cooling is maintained and life-saving interventions are performed.

7. Medical teams should be aware of the rare association with Malignant Hyperthermia (MH) muscle types. If sedation or anaesthesia is required, drugs which are known to trigger MH (for example, suxamethonium), should be avoided. The routine use of dantrolene is not currently recommended.

Complications and follow-up

8. Field and hospital medical teams should be aware of the complications of EHS, many of which may not be evident in the field setting and may present later, commonly in the first 24 to 48 hours. Initial blood biochemistry within the first few hours after EHS collapse may be normal and it is advisable to repeat the tests if symptoms are prolonged or delayed complications arise. Some of the complications of EHS are related to the systemic inflammatory response syndrome (SIRS) and include rhabdomyolysis and neurocognitive dysfunction, as well as renal, liver and multiple organ failure. Neurocognitive dysfunction includes disorientation and confusion, which may be chronic.

9. Following an episode of EHS, athletes should be followed up with clinical examination and repeat blood tests to ensure resolution of biochemical derangement. They should be advised to avoid all exercise for at least a week. When returning to exercise, the athlete may gradually increase exercise in a cool environment. Acclimatisation to exercise in the heat usually takes at least a further two weeks, and may be much longer. Guidance from a sports and exercise medicine physician may be useful if there are persisting clinical or biochemical abnormalities, or if return to exercise proves difficult. Heat tolerance testing may be useful, where facilities exist.

10. Athletes who have had an episode of EHS should be educated on the risk of developing further episodes.

©Faculty of Sport and Exercise Medicine UK, first published March 2014, reviewed and updated May 2018, next review due May 2021.

Authors: Dr Edward Walter, Dr Rob Galloway, Dr Mike Stacey, Dr Dan Martin, Dr Dan Roiz de sa, Dr Brian Robertson, Dr Courtney Kipps

References:

  1. McDermott BP, Casa DJ, Ganio MS, Lopez RM, Yeargin SW, Armstrong LE, Maresh CM. Acute whole-body cooling for exercise-induced hyperthermia: a systematic review. J Athl Train 2009; 44(1): 84-93
  2. Gagnon D, Lemire BB, Casa DJ, Kenny GP. Cold-water immersion and the treatment of hyperthermia: using 38.6°C as a safe rectal temperature cooling limit. J Athl Train 2010; 45(5): 439-44
  3. Belval LN, Casa DJ, Adams WM, Chiampas GT, Holschen JC, Hosokawa Y, Jardine J, Kane SF, Labotz M, Lemieux RS, McClaine KB, Nye NS, O’Connor FG, Prine B, Raukar NP, Smith MS, Stearns RL. Consensus Statement – Prehospital Care of Exertional Heat Stroke. Prehospital Emergency Care. 2018.

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