Hydration. Dehydration is an important risk factor for EHI. Sweat maintains thermoregulation by dissipating heat generated during exercise; however, it also contributes to body water losses. Furthermore, intravascular depletion decreases stroke volume, thereby increasing cardiovascular strain. It is estimated that for every 1% loss in body mass from dehydration, body temperature rises 0.22°C in comparison to a euhydrated state.6 Dehydration occurs more rapidly in hot environments, as fluid is lost through increased sweat production.7 After approximately 6% to 10% body weight volume loss, cardiac output cannot be maintained, diminishing sweat production and blood flow to both skin and muscle and causing diminished performance and a significant risk of heat exhaustion.7 If left unchecked, these physiologic changes result in further elevations in body temperature and increased cardiovascular strain, ultimately placing the athlete at significant risk for development of EHS.
Adequate hydration to maintain euvolemia is an important step in avoiding possible EHI. Multiple studies have shown that football players experience a baseline hypovolemia during their competition season,6 a deficit that is most marked during the first week of practices.17 This deficit is multifactorial, as football players expend a significant amount of fluid through sweat, are not able to adequately replace these losses during practice, and do not appropriately hydrate off the field.6,18 Some players, especially linemen, sweat at a higher rate than their teammates, posing a possible risk of significant dehydration.6 Coaches and players alike should be educated on the importance of adequate hydration to meet their fluid needs.
The goal of hydration during exercise is to prevent large fluid losses that can adversely affect performance and increase risk of EHI;6 it may be unrealistic to replace all fluid losses during the practice period. Instead, athletes should target complete volume replacement over the post-exercise period.6 Some recommend hydrating based upon thirst drive; however, thirst is activated following a volume loss of approximately 2% body mass, the same degree of losses that place athletes at an increased risk for performance impairment and EHI.4,6,11,12 Individuals should have access to fluids throughout practice and competition and be encouraged to hydrate as needed.6,12,15 Furthermore, staff should modify their practices based upon WBGT and acclimatization status to provide more frequent hydration breaks.
Hyperhydration and Salt Intake. Of note, there are inherent risks to hyperhydration. Athletes with low sweat rates have an increased risk of overhydration and the development of exercise-associated hyponatremia (EAH),6 a condition whose presentation is very similar to EHS. In addition, inadequate sodium intake and excessive sweating can also contribute to the development of EAH. EAH has been implicated in the deaths of 2 football players in 2014.1,6 Establishing team hydration guidelines and educating players and staff on appropriate hydration and dietary salt intake is essential to reduce the risk of both dehydration and hyperhydration and their complications.6Intra-Event Cooling. During exercise, team physicians can employ strategies for cooling athletes during exertion to mitigate their risk of EHI by decreasing thermal and cardiovascular strain.4,19 Cooling during exercise is hypothesized to allow for accelerated heat dissipation, where heat is lost from the body more effectively. This accelerated loss enables athletes to maintain a higher heat storage capacity over the duration of exercise, avoiding uncompensated heat stresses that ultimately cause EHI.19
Some intra-event cooling strategies include the use of cooling garments, cooling packs, and cold water/slurry ingestion. Cooling garments lower skin temperature, which in turn can decrease thermoregulatory strains;4 a recent meta-analysis of intra-event cooling modalities revealed that wearing an ice vest during exercise resulted in the greatest decrease in thermal heat strain.19 Internal cooling strategies—namely ingestion of cold fluids/ice slurry—have shown some mild benefit in decreasing internal temperatures; however, some studies have demonstrated some decrease in sweat production associated with cold oral intake used in isolation.19 Overall, studies have shown that combining external (cooling clothing, ice packs, fanning) and internal (cold water, ice slurry) cooling methods result in a greater cooling effect than a use of a single method.4
Tertiary Prevention
The goal of tertiary prevention is to mitigate the risk of long-term adverse outcomes following an EHS event. The most effective means of reducing risk for morbidity and mortality is rapid identification and treatment of EHS as well as close evaluation of an athlete’s return to activity in heat. This process is spearheaded by an effective and well-rehearsed emergency action plan.
Diagnosis and Management
Rapid identification and treatment of EHS is crucial to minimizing the risk of poor outcomes.7 Any delay in the treatment of EHS can dramatically increase the likelihood of associated morbidity and mortality.20