Outcomes of UK military personnel treated with ice cold water immersion for exertional heat stroke

Introduction: Despite mitigation efforts, exertional heat stroke (EHS) is known to occur in military personnel during training and operations. It has significant potential to cause preventable morbidity and mortality. International consensus from sports medicine organisations supports treating EHS with early rapid cooling by immersing the casualty in cold water. However, evidence remains sparse and the practice is not yet widespread in the UK.

Methods: Following changes to enable on-site ice cold water immersion (ICWI) at the Royal Marines Commando Training Centre, Lympstone, UK, we prospectively gathered data on 35 patients treated with ICWI over a 3-year period. These data included the incidence of adverse events (e.g. death, cardiac arrest or critical care admission) as the primary outcome. Basic anthropometric data, cooling rates achieved and biochemical and haematological test results on days 0-5 were also gathered and analysed.

Results: Despite being a cohort of patients in whom we might expect significant morbidity and mortality based on the severity of EHS at presentation, none experienced a serious adverse event. In this cohort with rapid initiation of effective cooling, biochemical derangement appeared less severe than that reported in previous studies. Higher body mass index (BMI) was associated with a lower cooling rate across a range of values previously reported as potentially of clinical significance.

Conclusions: This case series supports recent updates to UK military guidance that ICWI should be more widely adopted for the treatment of EHS. Clinicians should be aware of likely patterns of blood test abnormalities in the days following EHS. Further work should seek to establish the impact of lower rates of cooling and develop strategies to optimise cooling in patients with higher BMI.