Susceptibility to exertional heat illness and hospitalisation risk in UK military personnel

Abstract

BackgroundSusceptibility to exertional heat illness (EHI) is considered multifactorial in nature. The aims of this study were to (1) review traditional susceptibility factors identified in cases of EHI and (2) determine how they are related to risk of hospitalisation.MethodsReview of an electronic database of EHI reported in the British Army between 1 September 2007 and 31 December 2014. Cases were categorised by demographic, situational and susceptibility variables. Univariate and multivariate logistic regression was performed for the OR for hospitalisation by risk factor.Results361 reports were included in the analysis. 33.5% of cases occurred in hot climates, 34.6% in temperate climates during summer months and 31.9% in temperate climates outside of summer months. Traditional susceptibility factors were reported in 193 but entirely absent from 168 cases. 137 cases (38.0%) were admitted to hospital. Adjusted OR for hospitalisation was lower for recruits (OR 0.42, 95% CI 0.18 to 0.99, p<0.05) and for personnel wearing occlusive dress (OR 0.56, 95% CI 0.34 to 0.93, p<0.05) or unacclimatised to heat (OR 0.31, 95% CI 0.15 to 0.66, p<0.01).ConclusionsThe global, year-round threat of EHI is highlighted. Absence of susceptibility factors in nearly half of reports highlights the challenge of identifying EHI-prone individuals. Paradoxical association of traditional susceptibility factors with reduced hospitalisation risk may reflect the contemporary contexts in which severe EHI occurs. These findings also suggest a need for better evidence to inform guidelines that aim to prevent severe EHI concurrent to reducing overall morbidity.

Heat Adaptation in Military Personnel: Mitigating Risk, Maximizing Performance

“…It is less clear whether risk of more severe illness, such as heat stroke, is substantially ameliorated in the heat adapted phenotype (Lim and Mackinnon, 2006). An increased hospitalization risk for heat illness (as a surrogate for severity) has been reported in unselected military personnel considered acclimatized by attending physicians (Stacey et al, 2015). Hospitalization (Carter et al, 2005), and heat stroke deaths (Malamud et al, 1946) are less prevalent in military recruit populations originating from hotter regions, as opposed to cooler.…”

“…When an episode of heat illness occurs during, or soon after, strenuous physical exertion, it may be termed Exertional Heat Illness (EHI). This has been the predominant form of heat illness to affect British Army personnel in recent history, with EHI representing 96% of military cases reported by military doctors between 2009 and 2013 (Stacey et al, 2015) and continuing to make up the majority of referrals for specialist assessment. Most United Kingdom cases are incapacitated during training in temperate climates (Stacey et al, 2016).…”

The Impact of Mild Heat Stress During Prolonged Running On Gastrointestinal Integrity, Gastrointestinal Symptoms, Systemic Endotoxin and Cytokine Profiles

“…Cooling behaviours such as consumption of cold fluids, application of ice packs, fanning, water spraying, and/or reduced workload are common practices during physical exertion in hot ambient conditions ( ≥ 35 °C ambient temperature (T amb )), with the intention to mitigate increases in core body temperature and reduce the risk of heat-related illness [1,3,6,42]. Such cooling behaviours may not be of prime concern during physical exertion in milder ambient conditions (~30 °C T amb ), resulting in similar increases in core body temperature (i. e., ≥ 39 °C) and cases of exertional heat illness [8,38]. In association with ambient temperature, high relative humidity (i. e., ≥ 70 %) can impair heat dissipation thereby increasing thermal stress and contributing to high core body temperatures during low-to moderate-intensity exercise [30].…”

Thermoregulation and markers of muscle breakdown in malignant hyperthermia susceptible volunteers during an acute heat tolerance test

“…2 Even in races in the United Kingdom, EHI is a significant occurrence: in the 2009 Great North Run, 55 runners were admitted to the field hospital with deep body temperatures exceeding 41 °C. 3 In the British Army, 361 cases of EHI were reported between 2007-2015 of which 137 were admitted to hospital, 4 and in 2013 the deaths of three soldiers on a military training exercise in the Brecon Beacons were attributed to EHI. 5 It has been suggested that a skeletal muscle metabolic defect, similar to that responsible for malignant hyperthermia (MH) susceptibility could explain EHI in individuals with no obvious predisposing factors.…”