Exertional Heat Stroke


When their body temperature rises to dangerous levels, it can quickly become a life-threatening situation.1

What is Exertional heat stroke (EHS)?

EHS is one of the most severe of all heat-related illnesses2

  • EHS is a life-threatening medical emergency that occurs when a victim’s core body temperature is raised to dangerous levels due to physical activity.1,3-5
  • It is a hyperthermic and hypermetabolic crisis, associated with a rapid onset of central nervous system (CNS) dysfunction, which may lead to organ failure and death.1,3,6,7

EHS is not classic heat stroke

Exertional (EHS)

Primarily due to physical activity and environmental factors8,9

Onset to crisis within hours10

Often strikes relatively healthy people1,4

Classic (CHS)

Primarily due to heat exposure8

Onset to presentation within days1,10

More common in elderly, vulnerable populations1

EHS is both a hyperthermic and hypermetabolic condition in which calcium dysregulation may cause organ and neurologic damage5,11

The dysregulation of intracellular calcium, a key chemical messenger, may play a significant role in the neurologic and physiologic damage characteristic of EHS.11-13


Hyperthermia triggers intracellular calcium dysregulation, resulting in the neuronal dysfunction and death that is reflected in the clinical presentation and neurologic sequelae of EHS.11-13

Skeletal muscle cells:

Intracellular calcium is a critical messenger in the contraction of muscle. The hypermetabolism in EHS is marked by an uncontrolled escalation of intracellular calcium that causes a cascade of cellular events that can lead to severe muscular damage.11,14

In EHS, heat-dispelling mechanisms are overwhelmed by endogenous heat production causing an increase in core body temperature and metabolic demand.3,11

Who is at risk of developing ehs?

Although EHS can be a threat to anyone who exerts him or herself, some people are at higher risk than others

There’s no telling which physically active person EHS may strike, but we do know why it occurs3,8

Risk factors include3,8:

  • Hot-humid environment
  • Exercise intensity and duration
  • Inadequate heat acclimatization/poor physical fitness
  • Previous heat-related incident
  • Existing medical conditions
  • Currently taking medications
  • Dehydration

Despite knowledge of EHS risk factors, rates continue to rise2,8,18


CNS dysfunction is often the first sign of EHS2

Signs and symptoms include2,3:

  • Dizziness
  • Unusual behavior
  • Confusion
  • Change in personality
  • Irritability
  • Seizures
  • Collapse
  • Aggression

Immediate recognition and treatment are critical for survival and for reducing neurologic sequelae3,5,6

  • Without treatment, EHS victims can die within 1 hour of collapse7
  • Any delay in treatment can result in significant organ dysfunction, long-term neurologic damage, and death5,6,19
  • Treatment for EHS should be initiated if a victim receiving treatment for heat exhaustion does not improve within 20 minutes20

EHS is a cascading medical emergency1,21

  • The body’s inflammatory and hemostatic responses to heat stress can cause multi-organ failure if not treated rapidly and resolved14,19,21
  • Neuronal cell death begins above 104°F, and complications increase the longer a victim remains at or above this temperature13

The longer body temperature remains high, the greater the risk of complications, which in some cases may progress to multi-organ failure and death.13


Rapid, external cooling is a critical part of saving an EHS victim’s life5

Emergency departments use a variety of cooling techniques to treat EHS, but there are no universal guidelines.

External cooling may include5:
  • Ice packs
  • Evaporative cooling
  • Cooling blankets
  • Ice baths

External cooling doesn’t specifically address the hyperthermic and hypermetabolic crisis occurring in the brain2,5

  • Even after external cooling, internal body temperature can remain elevated5
  • Normalizing body temperature by cooling does not always prevent progression to multi-organ dysfunction21
  • Cognitive changes can develop 1 to 2 hours after a hyperthermic event ends13

Severe organ damage can still occur despite external cooling2,5

What is the impact of ehs?

As seen in two retrospective studies:

Surviving EHS does not mean the brain is safe from damage5:

  • Elevated temperatures in the brain may have immediate neurologic effects that persist past the acute EHS episode1,3,5
  • Even after external cooling, nearly 1/3 of cases had neurologic impairment at their 3-month follow-up5

Nearly 40% of EHS cases in the study ended in death or had poor long-term outcomes5

Long-term outcomes can include5,22:

  • Neurologic impairment
  • Liver failure
  • Renal failure
  • Hemorrhagic abnormalities

Victims who survive EHS can suffer from its long-lasting effects5

The following profiles are based on hypothetical patient scenarios and are not intended to represent actual patients. Choose a person to discover how their EHS story unfolded.

The Athlete

It was a 95°F day when Steve, a 21-year-old college football player, returned to preseason 2-a-day practices for his team. Steve had missed several days of practice due to an upper respiratory infection. Following a grueling morning workout, Steve began his afternoon with agility training and full-contact drills. Toward the end of practice, Steve began showing signs of confusion and agitation. He struggled to execute drills correctly and had to be prompted to begin. When coached regarding his performance, Steve was irritable and short-tempered. Concerned about his uncharacteristic behavior, trainers noted Steve was extremely hot to the touch. They found that his heart rate was elevated, and he had an oral temperature of 103°F. Steve was brought to the training room to receive cooling treatment, but became aggressive with his trainers and refused cold-water immersion. That’s when an ambulance was called.

At the hospital:

Forty minutes later, Steve arrived at the ER. EMS reported tachycardia and tachypnea, along with a rectal temperature of 104°F. Due to his extreme agitation and aggressiveness, benzodiazepines were administered and then an IV line was put in to administer fluids. The ER medical staff immediately initiated cooling with fans and misting. Within 2 hours, Steve’s body temperature returned to normal and he was transferred to the ICU for observation. While there, he remained confused and appeared to have had a tonic-clonic seizure.

3 months later:

Steve's overall condition is stable, but his neurological functioning did not fully recover. He is disoriented at random points throughout the day. He has no recollection of the day he had EHS, and now experiences memory impairment and mood swings. Steve's overall performance is diminished, mostly impacting his academic and social life. Also, it is not clear if Steve will ever be able to play college-level football again.

The Outdoor Worker

John was a 40-year-old overweight construction worker. After several months of unemployment, he returned to work for a large commercial roofing company. He was happy to be earning a paycheck again, even if it meant 8-hour days and overtime. His third day back on the job—a humid 90°F day—John spent the morning shingling a roof in the sun. At lunch, he mentioned to his coworkers that he felt light-headed and weak. Later that day, they noticed John was breathing heavily and acting confused. His coworkers reported his behavior to their supervisor, who observed John for a short time and then called an ambulance. By the time the ambulance arrived 20 minutes later, John had lost consciousness. Upon arrival, the EMS crew assessed John and concluded he had a Glasgow Coma Scale* (GCS) score of 6 (Eye response=2, Verbal response=1, Motor response=3).

At the hospital:

Forty minutes later, John arrived at the hospital with a rectal temperature of 105°F. He presented with elevated heart and respiratory rates and low blood pressure. EMS had performed an endotracheal intubation en route to protect the airway and had begun supplemental oxygen. They also initiated cooling via ice packs. Upon arrival to the ER, evaporative cooling measures were initiated with misting and fans. He was also given IV fluids. It took 1 hour for his temperature to come down to 101.4°F and, by that time, his labs indicated significant organ damage. Also, signs of brain edema on a head CT scan were noted by the radiologist. Despite efforts to manage his EHS and resulting complications, John was pronounced dead just 12 hours after the incident was first reported.

*The Glasgow Coma Scale (GCS) is a common scoring system used to evaluate the level of consciousness following acute brain injury.

The Firefighter

It was 9 AM on an 83°F day when Tony, a 32-year-old firefighter, responded to a structure fire. Tony was at the end of a long night shift, which had followed a full day of strenuous training. He hadn’t slept well and was mildly dehydrated. After 40 minutes of climbing and heavy lifting at the scene, Tony started to feel unsteady. As he exited the building, he lost his balance and fell. Other first responders helped Tony to his feet, but he was unable to retain his balance on his own. He complained of muscle cramping and fatigue. His mask and protective gear were removed. Tony was sweating, had hot skin, and was breathing rapidly. An ambulance was already on the scene. EMS recorded a rectal temperature of 104°F, tachycardia, tachypnea, and low blood pressure. EMS also recorded a Glasgow Coma Scale* (GCS) score of 11 (Eye response=4, Verbal response=3, Motor response=4). En route to the hospital, Tony was given a cooling vest.

At the hospital:

Upon arrival to the ER 20 minutes later, Tony’s baseline rectal temperature was 103°F, and he was disoriented. Emergency department medical staff commenced evaporative cooling using misting and fans. IV fluids were initiated; however, Tony developed rhabdomyolysis and acute renal failure, requiring admission to the hospital.

6 months later:

Tony sustained kidney and significant muscle damage and now requires physical therapy. Although Tony survived EHS, his career as an active firefighter is over.

*The Glasgow Coma Scale (GCS) is a common scoring system used to evaluate the level of consciousness following acute brain injury.

The Soldier

It was 8 AM on an 80°F day when Tara started her daily drills. After an intense workout alongside her unit, she began an 8-mile run at 11 AM. The previous day, Tara had felt ill with nausea and diarrhea. She avoided drinking and eating to prevent vomiting.

Although she was an experienced runner, on mile 6 her fellow soldiers saw Tara stumble repeatedly, become disoriented, and collapse. She regained consciousness, but her speech was incoherent. She was unable to regain full balance and had to be assisted into a vehicle. Tara was transported to the emergency medical unit on the base 5 minutes away for further assessment and treatment.

At the emergency medical unit:

Upon arrival, Tara’s rectal temperature was recorded at 104°F, and she was experiencing CNS dysfunction as evidenced by a Glasgow Coma Scale* (GCS) score of 11 (Eye response=3, Verbal response=3, Motor response=5). Her heart rate and respiratory rate remained elevated. She received immediate cooling with cold-water immersion. She was breathing on her own and did not require endotracheal intubation. Her body temperature dropped to 101°F within 1 hour. She was admitted to the hospital overnight for observation.

2 months later:

Tara is showing no lingering effects from her EHS episode. She has rejoined her unit, but takes precautions before drills and other strenuous physical activity.

*The Glasgow Coma Scale (GCS) is a common scoring system used to evaluate the level of consciousness following acute brain injury.