Frequently Asked Questions
What are EHI conditions?
EHI can range from mild to severe or even fatal conditions that occur when the body overheats. Though Service members may be relatively young and healthy, hundreds of military EHI or 'heat casualties', including 1 to 3 deaths, occur each year.
- Milder conditions (not reportable medical events)
- More serious conditions that can lead to permanent damage or be life-threatening (military reportable medical events):
- Heat exhaustion is when core body temperature has become elevated but remains below 104⁰F, observed signs/symptoms include dizziness, headache, nausea, weakness, unsteady gait, muscle cramps, fatigue; can resolve rapidly with immediate cooling interventions (moving to shade, loosening uniform/removing head gear, encouraging drinking but track volume (no more than 1.5 quarts of water over 1 hour).
Rapid intervention is necessary to prevent progression to heat stroke – casualty should be evacuated for further monitoring.
- Heat stroke is a life-threatening medical emergency when the core body temperature reaches 104⁰F or higher, and is most often observed by a change in mental status (confusion, delirium, combative, loss of consciousness), there may be vomiting, weakness, convulsions and chills. Call EMS or for
MEDEVAC and remove all outer clothing and initiate rapid cooling with ice sheets – the faster the body is cooled, the less damage to the brain and organs.
- Cover all but the face with ice sheets
- Ensure the ice sheet is soaked prior to applying to the casualty
- Switch ice sheets every 6 minutes with new ice sheets
- Evacuate immediately
- Hyponatremia, though not a reportable medical event, is also a life-threatening medical emergency. This condition occurs when too much water has been consumed resulting in a dangerous imbalance to the body’s chemistry. Like heat stroke, mental status changes may be noted and there may be repeated vomiting (clear vomit). Additional signs may include distended/bloated abdomen and large amounts of clear urine.
-
It is important to differentiate from heat stroke so determine if a casualty has consumed excessive water or fluids and/or had poor food intake.
- Verify hydration and sodium intake and call EMS or for
MEDEVAC
- Do
NOT give more water or IV fluids
- If awake, allow casualty to consume salty foods
- Evacuate immediately
What are risk factors for EHI?
In addition to the outdoor climate, the level, amount and frequency of vigorous activity, type of clothing and heavy gear, and individual health factors will impact how likely a person is to becoming a heat casualty:
- High heat is a primary EHI hazard,
so most EHIs occur between May and September, especially when the outside temperature is over 75° Fahrenheit (F). But heat causalities occur throughout the year.
Temperature, sunlight, humidity, and wind speed all affect heat illness risk. To combine these elements into a single Risk Category to allow unit leaders to manage operational risks, the military uses the Wet Bulb Globe Temperature (WBGT) index
to create Operational Risk Heat Categories. Leaders balance heat stress risks faced during their missions. Operational Risk Management of heat risks includes:
- Identify the hazards
- Know the WBGT
- Know the risk factors for heat illness
- Assess hazards
- Use the WBGT index to plan training activities
- Factor in training event, uniform/equipment requirements, location and time of day
- Know the acclimatization and profile status of your personnel
- Factor in previous days' condition, activities, and recovery time
- Develop controls
- Estimate heat Risk Category and follow appropriate work/rest guidance (link)
- Establish heat illness procedures and training leadership and all personnel
- Prepare water, medical, and evacuation support
- Implement controls
- Adjust activity distance, duration, time, pace, and/or load
- Provide water and/or electrolyte drink
- Avoid back-to-back strenuous days in the heat
- Supervise and evaluate
- NOTE: The WBGT is used by the military to determine “Flag Day" levels of risk by installations. Some installations are at higher risk than others due to routinely high WGBT, but –
- WBGT is required by military doctrine to be taken throughout the day at specific times and locations of an outdoor military activity to assess risk. This is because WGBT varies throughout the day AND can vary substantially at different locations on an installation.
- The amount of time exposed and number consecutive days of strenuous activities in high heat increases the risk of an EHI.
- Individual factors that increase susceptibility to heat illness include:
- Having had a prior heat illness
- Certain health conditions
- Poor fitness level (low aerobic fitness, and/or excessive weight)
- Certain medications
- Poor nutrition and inadequate hydration
- Excessive motivation (ignoring personal signs of physical limits)
What are the heat illness impacts to military readiness?
Heat illness, and dehydration from vigorous activity in heat, is a threat to individual health and to military operational success. Some supporting facts:
- Individually –
- Losing as much as 4% of body weight from dehydration can degrade physical performance.
- Every 1% loss of body weight increases core temperature (0.10-0.23⁰C or 0.18-0.40⁰F), thereby increasing risk of a more serious heat illness.
- Unit strength –
- Each year thousands of military heat illness casualties require medical attention
- In addition to medical care, the heat illnesses experienced by service members result in many thousands of lost/limited duty days each year
Resources
Department of Defense Guidance
Military Policy/Doctrine
Technical Journal Articles
- Exertional Rhabdomyolysis: Epidemiology, Diagnosis, Treatment, and Prevention (Knapik, 2016)
- Statement of the 3rd International Exercise-Associated Hyponatremia Consensus Development Conference (Hew-Butler, 2015)
- Within-Year Exertional Heat Illness Incidence in US Army Soldiers, 2008-2012 (APHC(P), 2015)
- Impact of Arm Immersion Cooling during Ranger Training on Exertional Heat Illness and Treatment Costs (DeGroot et al, 2015)
- Exertional Heat Illness and Hyponatremia: An Epidemiological Prospective (Carter III, 2008)
- Predictors of Hospitalization in Male Marine Corps Recruits with Exertional Heat Illness (Gardner, 2004)
- Hyponatremia Associated with Overhydration in U.S. Army Trainees (O'Brien, 2001)
Other Government Sites
