UK prehospital practitioners' knowledge of heat-related illness and heatstroke

Demographic data

Seventy-five respondents completed the questionnaire; their demographic details are shown in Table 1.

Clinical questions

The first clinical question of the survey asked what temperature defines heatstroke. Heatstroke is usually defined as having a core temperature >40.0°C or 40.9°C (Laitano et al, 2019). This was identified by 57% of respondents (Figure 1).

Regarding the management of heatstroke, respondents were asked to select which of six possible treatment options were suitable. The highest proportion (72%) selected sprayed water, with ice packs a close second, selected by 69% of respondents (Figure 2). Participants were able to select more than one answer.

Practitioners were also asked to select the correct order of treatment for a heatstroke patient (Figure 3). Cooling first and cooling en route were both selected by 47% of the responses. A small proportion (7%) of respondents selected cooling then discharging the patient from the scene with advice.

Respondents were asked to select any medications from a list that they thought could be useful in the management of heat-related illness (Table 2). The majority—71%—said no medications are useful for the acute management of heat-related illness. They were also asked which type of patient they felt was most at risk of dying from CHI. The commonest answers were men and elderly patients (Table 2 and Figure 4).

Participants were also asked what syndromes or diseases they believed could be caused by heatstroke. While the results varied (Figure 5), 95% thought heatstroke could cause kidney failure.

The respondents were then asked about the mortality of patients requiring intensive care because of classic heatstroke (CHS) and EHS. The commonest responses were a perceived mortality of 20–40% for both conditions (Table 2).

Finally, the participants were asked what they thought was the most accurate method of measuring body temperature in heat-related illness. More than half (53%) thought that rectal thermometry was the most accurate (Table 2).

Diagnosis of heatstroke

The diagnosis of heatstroke requires CNS dysfunction and a raised body temperature. The majority of respondents (Figure 1) correctly identified the temperature range that defines heatstroke. While the definition of heatstroke varies between sources, a non-systematic review identified that most sources define a minimum core temperature for diagnosis of 40.0°C or 40.9°C has (Laitano et al, 2019; Yezli et al, 2023) and 40.0°C been adopted by the American College of Sports Medicine (Roberts et al, 2023).

Treatment of heatstroke

The outcomes of patients with heatstroke have consistently been shown to be related to how rapidly their temperature was reduced.

A systematic review investigating the effect on the rate of cooling in EHS identified that a cooling rate of >0.15°C/min was associated with no deaths and a risk of medical complications developing of 0.77%, compared with a mortality rate of 4.41% and complication rate of 22.46% if the cooling rate were <0.15°C/min (Filep et al, 2020). A cooling rate of >0.15°C/min was recommended in a recent consensus statement (Belval et al, 2018).

Rapid cooling is also important in CHS. In one study, cooling to a rectal temperature of ≥38.9°C within 1 hour was associated with death in four of 27 individuals (15%) while, in the delayed cooling group, the mortality rate was four out of 12 (33%), a non-significant improvement (Vicario et al, 1986). In a second study, survivors of CHI were cooled to a core temperature of ≤38.5°C in an average of 2 hours compared with non-survivors, who achieved 38.5°C at 6.45 hours (Pease et al, 2009).

Techniques that provide rapid cooling rates, ideally ≥0.15°C/min in EHS, are therefore important. Immersion in cold water, fanning while being doused in water and the use of wet towels appear to be effective methods (McDermott et al, 2009) (Figure 6). In the survey, 53% of respondents considered that wet blankets and 72% considered that sprayed water would be effective. However, only 29% selected cold-water immersion as a possible treatment, although it is associated with cooling rates of 0.35°C/min and is recommended as the most effective treatment in EHS (McDermott et al, 2009). Ice packs used in isolation are less effective (McDermott et al, 2009).

However, availability of the above methods and the practicalities of performing some of them need to be considered. A majority (68%) of the respondents were working in prehospital roles at the time of the survey, or within the ambulance service, where access to some of these methods may be limited. At organised events, where having to manage EHI is anticipated, there may be greater opportunities to provide more effective methods of cooling, such as ice-water baths.

Priorities of treatment

With regards to treatment priorities, 47% of respondents stated they would actively cool patients with heatstroke before transport, and another 47% stated they would opt to transport with active cooling en route. The National Association of EMS Physicians (Belval et al, 2018) recommends that, in patients with EHS, immediate rapid cooling be undertaken until their temperature is <39.0°C before transportation. If the patient has other life-threatening conditions that necessitate rapid transport or if rapid cooling cannot be achieved, emergent transport to a location where cooling can be achieved or with cooling en route may be reasonable.

A minority of respondents (7%) stated they would cool the patient and then discharge with advice. Heatstroke is associated with a risk of multi-organ failure and death (Walter et al, 2016; Ward et al, 2020), long-term organ failure (Walter et al, 2016; Patel et al, 2023) and a risk of further episodes of heat-related illness, so hospital assessment, even if the patient has been cooled to a normal temperature in the prehospital phase, is generally recommended.

Medications to treat heatstroke

Over 70% of respondents correctly identified that no drugs are deemed useful in the context of managing heatstroke. Of the remaining 29% (19 individuals), the majority (14 participants) thought paracetamol would be useful, followed by nine respondents who thought dantrolene would be useful.

No drugs are recommended in the routine management of heat-related illness or heatstroke.

Dantrolene is a skeletal muscle relaxant used for muscle spasticity and in the management of malignant hyperpyrexia to reduce excessive muscle contraction and heat production. There are similarities between EHS and malignant hyperpyrexia but one review found the use of dantrolene was not associated with improvement in clinical outcomes in EHS (Hadad et al, 2005).

Antipyretic agents such as ibuprofen, aspirin and paracetamol may be useful in fevers in sepsis. However, the mechanism of fever in heat-related illness is different from that in sepsis; in addition, antipyretics may worsen the coagulopathy as well as hepatic and renal injury associated with heat-related illness (Walter et al, 2016) and should therefore not be used.

Demographics of patients most at risk from classic heat illness

Almost 70% correctly identified that older people are at the most at risk of dying from CHI (Centers for Disease Control and Prevention (CDC), 2022).

They may be more at risk than younger adults because they have lower cardiovascular physiological reserves, a diminished sense of thirst and compromised thermoregulatory systems resulting from senile degeneration (Walter and Carraretto, 2016). In addition, various medications, commonly taken by older people, such as diuretics and antihypertensives, may increase the risk of heat-related illness (Walter and Carraretto, 2015; Walter et al, 2016).

Older people may not develop classic signs of heat-related illness or report symptoms in the same way as younger adults, so a higher index of suspicion from clinicians is required (Bouchama et al, 2022; Yezli et al, 2023).

Heatstroke risk by sex

Of the respondents, 41% answered correctly that males are more likely to be affected by heatstroke than females.

A systematic review found that the incidence of women with heatstroke was in a range of 0.10–0.26 per 1000 person-years, almost half the incidence in men (0.22–0.48 per 1000 person-years) (Alele et al, 2020). The reasons for this are not clear, but may be related to endocrine or thermoregulatory differences, differences in muscle bulk and heat production or the protective effects of oestrogen (Chen et al, 2006).

In addition, this may be related to differences in work or employment patterns between the sexes; men may be exposed to higher temperatures during their work, for example, in the fire service, a predominantly male occupation (HM Government, 2022).

Organ failure from heatstroke

Heat-related illness is associated with thermal damage to a wide range of organs, which is not always appreciated by clinicians. Heatstroke can cause dysfunction of the kidney, liver, heart, central nervous system and blood (Walter et al, 2016).

Most respondents (95%) agreed that heatstroke can lead to renal failure. Renal dysfunction is common in both CHS (Yezli et al, 2023) and EHS (Sithinamsuwan et al, 2009; Satirapoj et al, 2016; Wu et al, 2021), and may be severe enough to require renal replacement therapy (Sithinamsuwan et al, 2009; Satirapoj et al, 2016; Kaewput et al, 2021; Wu et al, 2021). There is also a risk of chronic kidney disease developing, reported to be at a rate of 8.8% over 13 years, around double the normal rate (Tseng et al, 2020).

A smaller proportion of respondents were aware that heatstroke can also cause dementia (8%) and spinal cord damage (11%). A wide range of short-term and long-term neurological and cognitive symptoms and dysfunction have been described in both EHI and CHI (Walter et al, 2016).

Liver failure is a recognised complication from both CHI and EHI and may be severe enough to warrant transplantation (Coenen et al, 2017; Ichai et al, 2019).

Shock and hypotension may be present in patients presenting acutely, and electrocardiogram changes are common, being reported in over 61% of patients with CHI in one series (Yezli et al, 2023). There may also be an increased long-term risk of ischaemic heart disease (Tseng et al, 2019) and heart failure (Wang et al, 2019).

Mortality from classic and exertional heatstroke

Both forms of heatstroke are associated with a risk of death. In patients requiring intensive care with CHS, mortality is estimated at 63.2% (Bouchama et al, 2022), higher than the 20–40% estimated by the majority of respondents in this survey (Table 2).

In patients admitted to intensive care with EHS, the mortality is lower, estimated at 26.5% (Bouchama et al, 2022); this was the commonest answer from the respondents.

The difference in mortality may be related to demographic differences. Exertional heatstroke more commonly affects younger, fitter individuals; CHS more commonly affects older patients who, as discussed above, are at higher risk of death.

Accuracy of temperature measurement

It must be noted that peripheral and core temperatures are different. The peripheral temperature is that of the skin, which can be affected by blood flow to the skin and environmental temperature. Commonly used sites include the mouth, ear and skin. The core temperature refers to the temperature of the deep body tissues, such as the brain and heart. It is commonly measured in the oesophagus or rectum.

Oral temperature measurement is easily carried out, but factors such as probe placement, ambient air temperature and fluid ingestion may influence readings. Oral temperature measurement may be inaccurate; it can under-read by >0.50°C at normal temperatures and by >1.5°C at temperatures approaching 39°C (Mazerolle et al, 2011).

Tympanic or aural thermometers use infrared lasers to measure the temperature of the external auditory canal but, as with oral temperature measurement, tympanic thermometers can underestimate raised core temperatures, with a mean difference of 1.72°C when >39°C in one study (Huggins et al, 2012), which may hinder recognition or treatment.

Central or core temperature measurement gives a more accurate assessment of core body temperature than peripheral (Lefrant et al, 2003). Rectal temperature measurement differed from true core temperature by −0.07 ±0.40°C) and oesophageal temperature measurement by +0.11 ±0.30°C in one study (Lefrant et al, 2003); however, the latter may not be as readily available or practical in the prehospital setting.

More than half of respondents selected rectal measurement and 32% oesophageal as the most accurate measurements. Both would be considered to have similar accuracy and, if available, are the recommended sites. Tympanic, oral and axillary measurements, selected by 15% of respondents, are generally less accurate.