Heat Illness Print

Heat illness is a serious problem in sports and is the second leading cause of death in athletics behind head and spinal trauma. Many sports require vigorous activity in high heat, high humidity environments and therefore subject their participants to the risks of heat illness. Sports that require bulky uniforms and layered padding, such as football, are particularly risky.

The human body has an amazing capacity to adapt to its environment. The body responds to heat by sweating, vasodilation and exchanges heat with breathing. Sweating is a very efficient mechanism to regulate heat in that water conducts heat 25 times faster than air. However, this rapid loss of heat comes at the expense of lost electrolytes that must be replaced.

The best way to avoid heat illness is through acclimatization, avoiding vigorous activity in extremes of heat and humidity, fluid and electrolyte replacement and frequent rest to allow the body to cool. Acclimatization takes from 3 weeks to 2 months and has the advantage of making the body more efficient in dealing with excess heat. Changes that occur include:

  • Metabolic efficiency is enhanced to increase aerobic metabolism in skeletal muscle, which produces less heat than anaerobic metabolism.
  • Sweating is initiated at a lower core temperature and volume increases from an avg. of 1.5 liters per hour to 3 liters per hour.
  • Increased stroke volume and cardiac output in the heart to decrease the heart rate.
  • Enhanced retention of sodium by the kidneys and sweat glands

When vigorous activity is undertaken in extreme environments, frequent rest periods are necessary. Rest periods should be at least 20 minutes long to allow absorption of fluids. In general, rest in a cool place with fluid replacement containing electrolytes is best. "Salt pills" are usually not necessary as most "sports drinks" contain electrolytes, and any remaining deficiencies can be replaced at meals.

When the body becomes dehydrated, the loss of water can be measured by loss of body weight. A 3% loss of body weight requires immediate fluid replacement. A 5% loss precludes further participation and a 7% loss requires immediate medical attention.

Predisposing Factors

  • Lack of acclimatization
  • Extremes of heat and humidity
  • Inappropriate clothing such as heavy pads or uniforms
  • Insufficient rest and fluid replacement
  • Obesity
  • Anticholinergic drugs that decrease sweating
  • Young age

Heat Illness Syndromes

Prickly Heat: Prickly heat is a reddish rash that develops in skin that is exposed to constant moisture such as unevaporated sweat. This condition is self limited and requires only several days in a cool dry environment.

Heat Edema: This is a condition that present with swelling in the hands and feet when held in a dependent position. This is also a self limited condition that responds to cooling and elevation.

Heat Tetany: This condition manifests as muscle spasms, usually in the hands and fascial muscles, caused by metabolic disturbances from hyperventilation. This hyperventilation leads to decreased levels of carbon dioxide which changes the pH of the body, altering the calcium level in the blood. The change in calcium concentration leads to muscular spasms. This condition requires immediate cooling of the body with adequate fluid replacement.

Heat Syncope: Postural hypotension and fainting can occur from massive vasodilation and blood pooling. This can generally be treated by rest and fluid replacement in a cool environment.

Heat Cramps: When athletes exercise in hot environments, profuse sweating causes massive losses of water and electrolytes. When sodium is lost and not replaced, working muscles begin to cramp. This must be treated with rapid rehydration and electrolyte replacement, sometimes requiring intravenous fluids. This should not be treated with "Salt pills’ due to the possibility of gastric irritation and vomiting.

Heat Exhaustion: Patients present with nausea, vomiting, loss of appetite, headache, dizziness and weakness. They often have a rapid heart rate, low blood pressure, irritability and may lose consciousness. This is a serious condition which requires immediate cooling and fluid replacement to prevent heat stroke.

Heat Stroke: Patients present with a very elevated core temperature, sometimes above 105 degrees. Central nervous central dysfunction is common which may lead to seizures or even coma. At this point, the body has lost its ability to regulate heat and rapid deterioration occurs. The marked elevated temperatures, critical dehydration and electrolyte imbalances damage cells and may even lead to generalized bleeding as normal blood clotting fails. This is an extremely critical condition and has a reported mortality rate of 10 to 80%. Treatment requires immediate cooling by removing the clothing and moving to a cool environment. Ice should be applied to the torso and extremities and the body should be covered in cool rags. Immediate medical attention is warranted and fluid replacement will require hospitalization.

It should be noted that the above syndromes represent a continuum from mild to very severe. As the dehydration and electrolyte imbalances progress, mild symptoms can rapidly become life threatening, so it is important to recognize the early signs of heat illness, so intervention can disrupt this dangerous cycle.

Orthopaedic Sports Medicine, Nashville, Dr. Allen F. Anderson, Heat Illness, Fig. 1

Figure 1

Orthopaedic Sports Medicine, Nashville, Dr. Allen F. Anderson, Heat Illness, Fig. 2

Figure 2

© Allen F. Anderson, M.D. 2017