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Abstract
This article introduces a practical triage tool designed to assist commanders, jungle training instructors (JTIs) and medical personnel to identify Defence Personnel (DP) with suspected exertional heat illness (EHI). The challenges of managing suspected EHI in a jungle training environment and the potential advantages to stratifying the urgency of evacuation are discussed. This tool has been designed to be an adjunct to the existing MOD mandated heat illness recognition and first aid training.
- exertional
- heat
- injury
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Introduction
Exertional heat illness (EHI) is the term used in the context of a heat illness precipitated during military training. The normal mechanisms of thermoregulation are disrupted, leading to incapacitation as a result of a rise in core body temperature (Tc).1While the military experience of heat illness, its underlying pathophysiology and general risk factors are understood,2 3 the underlying pathogenesis of individual susceptibility remains elusive.4 Collective organisational responsibility, force preparation and preparedness through effective education and military training may help mitigate the risk, but EHI remains a significant source of morbidity and mortality during military training and operations in thermally stressful environments. This may be due in part to the idiosyncratic response of individual Defence Personnel (DP) to thermal stress.5 Commanders remain challenged to provide realistic training to appropriately prepare DP while also reducing risk as much as possible.6 The aim of this article is to introduce a practical triage tool designed to assist commanders, jungle training instructors (JTIs) and medical personnel to identify DP with suspected EHI. The challenges of managing suspected EHI in a jungle training environment and the potential advantages to stratifying the urgency of evacuation are discussed. The authors hope to stimulate a discussion around the triage and early treatment of EHI in the jungle.
Medical support to jungle training
Alongside the operational imperative to deliver combat effectiveness in the jungle, this environment offers a uniquely oppressive physiological and psychological backdrop in which to conduct military training. Operating effectively in this environment requires the highest standards of personal field administration and military tactics. Experiences in Burma and Malaya confirm the unforgiving and physiologically erosive nature of jungle campaigns.7 8 Wet bulb globe thermometerare common in jungle microclimates. The physical effort required to operate in such environments often exceeds the WBGT index limits for key activities including close quarter contact drills and long-range patrolling.1
Typically, medical support to a jungle training exercise will include a medical treatment facility (MTF) colocated at or near the Jungle Base Camp (JBC). Clinical care is led by a Medical Officer supported by Combat Medical Technicians, Paramedics or Nurses. The MTF maintains a supply of ice packs and chilled intravenous fluids. Medical personnel are often deployed across the training area in order to pre-empt and mitigate EHI risk during specific training activities.
Casualty evacuation timelines remain a constant challenge in the jungle; movement from the training area to the MTF may take longer than 60 min. Moving casualties on stretchers through this terrain is difficult, and potentially dangerous to casualties and their evacuation teams. Helicopter medical evacuation is not a panacea. Retrievals are usually limited to daylight hours and may be prolonged, whether using winches (which in themselves expose all parties to significant risk if winching through the jungle canopy) or pre-prepared helicopter landing sites.9 There are also considerable risks associated with helicopter transfer of unstable, heat-injured casualties whose behaviour can become aggressive and combative. Road moves may prove safer, but in many instances can take over 12 hours.
The clinical challenge
Fatigue, thirst, headache, nausea, cramps, lightheadedness and diarrhoea commonly affect those undertaking jungle training. Individuals display idiosyncratic responses to thermal stress, which can make it difficult for Medics and JTIs to distinguish between those DP who are developing the early symptoms of an EHI and those who are ‘only’ fatigued. It is neither safe nor practical to evacuate every suspected case of EHI to a MTF. Accurate measurements of Tc are difficult to obtain. Currently, Tc is recorded using tympanic thermometers or rectally using gloved oral thermometers. To help overcome some of these challenges, an experimental triage tool is proposed to help identify and prioritise DP who may be experiencing EHI.
The EHI triage tool
The EHI triage tool illustrated in table 1 is based on a Major Incident Medical Management and Support (MIMMS) triage sort.10 It incorporates current and extant Joint Service Publication 539 guidance1 on the management of acute EHI. The scoring system combines quantifiable physiological parameters (temperature, pulse rate and respiratory rate) with functional observations (level of consciousness, continence and vomiting). The ranges and thresholds for evacuation have been determined through an iterative process of combining clinicians’ qualitative experience of jungle heat casualties with post exercise analysis of the clinical data from DP evacuated with potential EHI. The physiological scores on the triage card were retrospectively compared against the corresponding biochemical results to identify threshold physiological values and symptom patterns. This information has been used to refine the sensitivity and specificity of the tool. Tc above 40°C has received a relatively low weighting as body temperature alone is an unreliable guide to severity.1 Physiological and functional scores are summed. The total derives a suggested action as shown at the bottom of the tool.
EHI triage tool
Symptomatic DP with a triage score of 0–2 should be carefully monitored and reassessed after 30 min of rest, active cooling and oral rehydration. This 30 min ‘cooling off period’ allows for a treatment phase and a subsequent period of physiological response and clinical trend interpretation. On the basis of the authors’ experience, DPs’ physiological response to early treatment is a strong marker of prognosis. Those who recover fully may continue at risk, but still require close supervision. Depending on their progress, those not recovering fully should either be returned to the MTF for further assessment or potentially evacuated to hospital. DP whose initial triage score is 3 or more should be evacuated to hospital immediately.
In addition to the heat illness recognition and first aid training mandated by the Ministry of Defence (MoD), JTIs receive additional training on how to assess pulse rate, respiratory rate, neurological signs, tympanic and rectal temperatures. A series of medical moulages based on previous clinical cases have been introduced to assure JTIs’ clinical skills and improve their familiarity with the triage tool. After each training cycle, the tool has been refined, using feedback from the training team to improve ease of use and quality of the management advice. Issued as a laminated casualty card, the triage tool guides the user through a structured clinical assessment by prompting for physiological measurements and basic clinical observations. The resulting scores recorded over time provide a trend that combined with the casualty’s progress leads to a suggested course of action. It is the authors’ intention that the triage card provides a contemporaneous prehospital clinical record that can be used to improve casualty care through quality improvement programme.
Discussion
The EHI triage tool has now been utilised within eight cycles of jungle training over a 5-year period. Despite adherence to mandated MoD acclimatisation and training protocols, even DPs who are considered ‘low risk’ sometimes succumb to the thermal stress of the jungle.4 Retrospective analysis of the triage cards for those DP requiring treatment for a suspected heat illness fell into four cohorts. The first were those personnel who had an initial Tc between 38 and 40 degrees and a triage score of 2 or less. This cohort recovered within the 30 min and was deemed fit to continue ‘at risk’. Those individuals who were deemed ‘fit to continue’ did so successfully, neither requiring further medical treatment nor evacuation within the next 24 hours period. The second cohort presented with similar physiological scores that did not normalise during the 30 min treatment and observation period. They were evacuated for further assessment and treatment. Their subsequent blood tests did not reveal any significant biochemical abnormalities. In the authors’ experience, the first two cohorts may represent a group that had suffered exhaustion from exercising in extreme conditions and were not suffering from heat illness. Literature in this field describes subjects reaching a functional ceiling of heart rate as a consequence of exercise induced circulatory stress precipitated by environment stress.11 These subjects recovered quickly once removed from the thermal stress and were able to continuing working. This description closely matches the authors’ own observations in the jungle.
The third cohort presented with similar physiological scores that did not normalise during the 30 min treatment and observation period. They were evacuated for further assessment and treatment. Their subsequent blood tests showed some biochemical abnormalities. The changes in biochemistry did not demonstrate any particular pattern and the magnitude of change did not correlated to the individual’s Tc. Changes were most commonly observed in creatinine phosphokinase and liver function tests. The fourth cohort had an initial Tc between 38 and 41 degrees and a triage score of greater than 3 often with associated physical signs. This small number of individuals was noted to be very unwell and had significant derangement across the spectrum of biochemical markers of heat illness. In after-action reviews, the majority of DPs who had experienced EHI were found to have no intercurrent illness or other known precipitating factors. This observation has been corroborated from elsewhere in the literature.12
In the authors’ opinion, this triage tool is generalisable to all jungle training environments but recognise the limitation that this triage tool has not been validated. There is a need to validate this tool through a rigorous clinical trial. There also remain practical difficulties obtaining accurate Tc in jungle and other prehospital environments. Ongoing biosensor research may reduce these difficulties. In future, -software-based triage algorithms or medical early warning systems (MEWS) could use such data to advise and inform clinicians and commanders.
Conclusion
This article describes the common logistical and clinical challenges facing Commanders and medical staff in delivering safe but appropriately challenging jungle training. The idiosyncratic nature of an individual’s response to thermal stress can make the diagnosis of mild to moderate cases of EHI very difficult. With further refinement, the authors believe that the triage tool could enhance the ability to diagnose EHI and provide appropriate early guidance on evacuation priority. It is envisaged that the EHI triage tool would become a useful adjunct to the MoD’s mandated heat illness recognition and first aid training in all jungle training environments. At present there is no valid and reliable means of assessing individual vulnerability to EHI. It is hoped this triage tool may assist commanders to optimise their training opportunities in austere jungle environments without compromising our duty of care to MoD personnel.
Footnotes
Contributors All three authors contributed to the writing of this manuscript.
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.