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Disaster Responder Heat Stress



Michael Heaney¹, Ian Norton¹,² and Matt Brearley²
Royal Darwin Hospital, Darwin, Australia
² National Critical Care & Trauma Response Centre, Darwin, Australia

Aims: To assess the physiological responses of medical responders to simulated field emergency in tropical conditions, and to provide guidelines to limit body heat storage and dehydration in tropical conditions.

Methods: 10 subjects, all of whom were chronically heat acclimatized health care workers (predominantly doctors and nurses) volunteered to participate in this investigation. Participants were the medical response team of a simulated field emergency conducted at the Northern Territory Emergency Services training grounds, Yarrawonga, NT. The exercise consisted of setting up a field hospital, transporting patients to the hospital, triaging and treating the patients while dressed in their standard medical response uniform in field conditions (mean ambient temperature of 29.3°C and relative humidity of 50.3%, apparent temperature of 27.9°C) for a duration of 150 minutes. An integrated physiological monitoring device worn by each participant measured and logged heart rate, skin temperature (chest) and gastrointestinal temperature throughout the exercise (Equivital, Hidalgo Ltd, Cambridge, UK). Gastrointestinal temperature was transmitted from an ingestible sensor and used as the index of core temperature. Dehydration and hydration status were assessed by monitoring the change between pre- and post-exercise body mass and urine specific gravity (USG). Participants had ad libitum access to fluids via a wearable hydration backpack containing water.

Results: Mean core temperature rose from 37.5°C at the commencement of the exercise to peak at 37.8°C after 75 minutes. The individual peak core body temperature was 38.5°C, with only 2 subjects exceeding 38.0°C. Subjects sweated 544mL per hour and consumed 355mL of fluid per hour, resulting in overall dehydration of 0.67% of body mass at the cessation of exercise.

Conclusions: The combination of the unseasonably mild environmental conditions and moderate work rates resulted in minimal heat storage during the simulated exercise. As a result, low sweat rates manifested in minimal dehydration. When provided with good access to fluids in mild environmental conditions, chronically heat acclimatised medical responders can meet their hydration requirements through ad libitum fluid consumption. Whether such an observation is replicated under a harsher thermal load remains to be investigated.

Contact Disaster Medical Research Manager, Matt Brearley for more information via, (08) 89226422 or 0420899399.