CPR Seattle Blog

Learn more about Safety, CPR and First Aid

Heat Exhaustion and Heat Stroke: What’s the difference?

There are several stages of heat-related illness that we discuss in the American Heart Association Heartsaver First Aid course. While anyone can suffer the effects, this is especially dangerous for those who may be in high-risk groups, such as children under 4, adults over 65, those with diabetes, heart disease, or mental illness. Persons taking certain medications such as diet pills, blood pressure medications, antidepressants (Prozac, Zoloft) or drugs such as LSD or Ecstasy are also at a higher risk. Those who live in urban areas may experience the “heat island effect”, where concentrations of roads and building absorb heat during the day and then slowly release it a night, resulting in higher nighttime temperatures.

There are usually two stages of heat-related illness (hyperthermia) referred to by name; “heat exhaustion” and “heat stroke”.

Heat exhaustion (also referred to as heat prostration, or heat stress) is a heat-related illness that can develop after exposure to high temperatures. It is often accompanied by dehydration. Generally, heat exhaustion occurs because of water depletion or salt depletion.

When in high temperatures, the body can lose up to 2kg per hour in sweat, over several hours. The fluid that the body sweats comes from blood plasma. When overheating begins, blood vessels in the skin dilate, drawing blood into them. Sweat glands move the plasma to the skin for evaporation and cooling.

High activity exacerbates the problem – the blood required for cooling is now also being demanded by the muscles doing the work. Initially, this can cause fainting, as the blood pressure needed to get blood to the brain can’t be maintained. Sometimes, those persons experiencing overheating pass out not while exerting themselves, but when they stop to rest – the muscle activity in the lower body prevents blood from collecting in that area.

The signs of Heat exhaustion can include (but are not limited to):

  • Muscle or abdominal cramps
  • Confusion
  • Pale skin
  • Profuse sweating
  • Dark-colored urine (a sign of dehydration)
  • Dizziness
  • Rapid heartbeat/fast, weak pulse
  • Fainting
  • Fatigue
  • Headache
  • Nausea, vomiting, or diarrhea

If these symptoms are observed, it is essential to get the victim out of the heat and allow them to rest. Hydration with plenty of fluids (no caffeine or alcohol) and the removal of tight or unnecessary clothing will assist in recovery. If it is possible to get the victim into a cool shower or bath, do so. Other measures such as cool, wet towels and fans can also be used to help cool them down. If these measures do not provide relief in 15 minutes, then activate emergency services, as heat stroke may be developing.

Heat stroke (also known as sun stroke) can occur when milder heat-related illnesses are not alleviated and exposure to high temperatures is prolonged.  Heat stroke is defined by a high core body temperature (sometimes greater than 105 degrees Fahrenheit) with complications affecting the nervous system. This condition constitutes a medical emergency – if anyone suspects heat stroke in a victim, 911 should be notified immediately. Basically, the body’s temperature control system fails because it cannot effectively dissipate the heat that it is absorbing.

As the competition for blood by the various parts of the body increases, the internal organs end up on the losing side. Cut off from their support system, they don’t get oxygen replenishment or glucose for fuel, and waste products aren’t carried away. Bacteria may start to leak into the blood, digestive organs shut down, and widespread inflammation results. Altered consciousness, coma, and even death can result.

Symptoms of heat stroke can include:

  • Hot, dry skin (the blood vessels are dilated to increase heat loss)
  • Nausea/vomiting
  • Severe muscle cramping
  • Headaches
  • Low blood pressure
  • Fainting/dizziness
  • Confusion, disorientation, altered behavior
  • Rapid heart rate (tachycardia)
  • Seizures (especially in children)
  • Rapid, shallow breathing
  • Unconsciousness

While waiting for emergency services to arrive, move the heat stroke victim to a cool environment (preferable air-conditioned) and remove any unnecessary clothing. If possible, immerse the victim in cool or cold water up to chest level (remove them from the water once they exhibit signs of recovery). If that isn’t possible, then douse the skin with water and fan the victim vigorously. Ice packs (or packages of frozen vegetables from the freezer) should be applied to the victim’s neck, back, armpits and insides of the thighs.

Sensitivity to heat may be noticed in the week following recovery from heat-related illnesses; it’s best to avoid hot weather and excessive exercise until a doctor gives the all-clear.

The best way to avoid these conditions is to limit exposure. Wearing light-colored, loose clothing will help reflect heat and allow for evaporation. Drinking extra fluids (again, no alcohol or caffeine), especially during exercise or heavy work, will help reduce dehydration. Even better is to put off such activity until the temperature has dropped to safer levels. Stay safe by paying extra attention to the heat index – the combination of air temperature and relative humidity – and limit activity when the index is over 90 degrees.


Published on November 15, 2016