Heat Related Illness
What is Heat Related Illness?
Heat related illness occurs when the body is unable to adequately preserve a constant internal temperature due to both intrinsic and environmental stressors. It encompasses a wide range of issues from simple heat edema and heat rash to the life threatening condition of heat stroke.
It is estimated that up to 400 deaths a year occur due to heat related illnesses and is felt to be the 3rd most common cause of death in athletes behind cardiac and head/neck injuries. The majority of heat related problems present as cramps and or edema. Cases of heat exhaustion and heat stroke are more rare, but also much more serious.
What are the different types of Heat Related Illnesses?
As mentioned Heat Related Illnesses span a wide spectrum of problems and severity. It is also important to note that this spectrum is not necessarily a continual progression. Heat Related Illnesses include heat edema/rash, heat cramps, heat syncope, heat exhaustion, and finally heat stroke.
What is the normal response to heat?
The body produces about 20 times more energy at maximum exertion versus rest and the majority of this energy is converted to heat. The body responds to even a 1 degree Celsius increase in core temperature. The body attempts to regulate body temperature through a variety of methods including peripheral vasodilatation, diverting of blood from the internal organs to the skin to promote cooling, sweating, increased breathing, and an increase in the blood being pumped by the heart. The body’s perception of exertion is increased with increasing humidity and temperature meaning that the body reaches an exhausted state sooner. The body’s ability to cool itself is dependent on a gradient of temperature and moisture between itself and the environment. This means that as the temperature and humidity of the environment increase, the body’s ability to cool itself decreases.
What are the normal cooling methods used by the body?
The main methods of heat exchange employed by the body are conduction, convection, radiation, and evaporation. Conduction involves cooling by direct contact with cooler objects. Convection depends on cool air surrounding the body. It is dependent on airflow and circulation making domes and areas with decreased wind problematic. Radiation involves direct release of heat into the environment but is reliant on body temperature being higher than ambient temperatures. Evaporation is the most effective of the four methods and includes perspiration.
Who is at risk for Heat Related Illness?
Heat related illness is a concern for any athlete. Rectal temperatures up to 107.4 degrees Fahrenheit have been documented in soccer players, football linemen, and runners, all of whom were asymptomatic at the time. Certain variables that may be of concern include environmental stresses, the individual’s level of acclimization to the environment, as well as medications, patient age, and any co-morbid conditions the patient may have.
What are the symptoms of Heat Related Illness?
Heat Edema involves dependent soft tissue swelling of the extremities. It is often caused by vasodilatation and prolonged standing. It is rare to see in the well-conditioned athlete, but may be present in those not acclimatized to the environment.
Heat Rash is caused by occlusion of sweat ducts causing the leakage of sweat into the surrounding tissues. This leads to a burning and itching rash. It is seen in patients with excessive sweating. It is often seen in areas that are constricted by clothing such as the waist, trunk, axilla and groin.
Exertional heat cramps present as painful spasms in the upper extremities, abdomen, quadriceps, hamstrings, and calf muscles. They often occur following prolonged, strenuous exercise in excess of 2 hours and especially in hot environments and often in association with muscle fatigue. It is frequently seen in football, tennis, soccer, and long distance running. There is no evidence that heat cramps are a predictor of heat exhaustion or heat stroke. They are felt to be due to sodium loss, fluid loss, and inadequate electrolyte and fluid replacement.
Heat Syncope is classified as syncope or near-syncopal episodes seen after significant exertion once stopped, with prolonged standing, or rising from a seated or lying position. It is felt to be due to dilatation of the peripheral vessels, loss of lower extremity muscle contraction and pooling of blood in the veins. It can occur during the cool down phase of exercise and therefore it is recommended to keep athletes moving after activity such as after a marathon. Symptoms usually resolve with return of blood to the central circulation.
Heat Exhaustion presents with symptoms of fatigue, dizziness, nausea, fainting, committing, headache, and weakness. Heavy sweating and cold, clammy skin are often seen. Core body temperatures are in the range of 98.6-104 degrees Fahrenheit. The neurologic status is stable and patients demonstrate normal mentation, an important distinguishing factor. Symptoms usually resolve rapidly with proper treatment. Left untreated, heat exhaustion can progress to heatstroke and therefore must be recognized and treated early.
Heat Stroke is the most serious of the constellation of heat related illnesses. It is life-threatening if left untreated. The classic triad of symptoms includes core temperatures in excess of 104 degrees Fahrenheit, profuse sweating, and neurological disturbances such as difficulty walking, confusion, irritability and coma. There are many risk factors for heat stroke including environmental as well as individual factors. Use of certain medications or supplements, alcohol use, obesity, improper clothing or equipment, and deconditioning may all predispose an individual.
How are Heat Related Illnesses treated?
Treatment for these problems is somewhat problem dependent. The mainstay of treatment for all of the disorders is to attempt to remove the individual from the causative factor and attempting to lower their body temperature. Rest, hydration, and cool mist techniques are treatment techniques for the more benign conditions. Heat exhaustion and heat stroke require more aggressive treatment involving oral fluids if possible and or IV fluids for cooling and rehydration. Total body cooling is required for heat stroke including ice water immersion techniques, ice packs to the neck, axilla, and groin, as well as monitoring of core temperature and vital signs. Early transfer to a medical facility for further cooling and evaluation is also required.
How can Heat Related Illness be prevented?
The cornerstone of treatment for all of the heat related illnesses is prevention. Appropriate hydration and acclimization to the environment is very important. Education of parents, coaches, and trainers of the warning signs to look for can also make a big difference in recognition of problems early. The use of more gradual training programs by athletic teams, especially at the beginning of the season, has also been promoted recently.
L. Armstrong et al. Exertional Heat Illness during Training and Competition. ACSM position statement 2007.
Casa, D.J., et al. Curr Sport Med Rep 2005, 4: 115-127.
Bergeron, M.F, McKeag, D. et al. Youth Football: Heat Stress and Injury Risk. Med Sci Sports Exerc 2005 Aug 37 (8): 1421-1430.
Eichner, E.R. Heat Illness in Football. Presented at AMSSM Annual Meeting, 2005 April, Austin, TX.
Wexler, R. Evaluation and Treatment of Heat-Related Illness American Family Physician. June 1, 2002.
Pratt, A. Putting the Chill on Heat-Related Illness. Contemporary Pediatrics. June 2005, vol 22, no. 6.
Coris EE et al. Heat Illness Symptom Index (HISI): a novel instrument for the assessment of heat illness in athletes. South Med J. 2006 Apr; 99(4): 340-5.