Heat Exposure Syndromes and Fluid Replacement - Part I
Heat stroke deaths still occur in high school football and college wrestling. It can also occur in other sports during the hot summer months. Environmental heat-induced deaths can be prevented. In recent years, educated coaches have significantly helped in decreasing the incidence of heat-related deaths in athletes. This article will detail some of the causes of dehydration and heat illnesses as well as preventative measures that the athlete, his family and the coaching staff can undertake.
Sweating and Electrolyte Loss
Sweating begins when the body is challenged by elevated environmental temperature. Sweat production increases sharply with increasing temperature and can result in loss of more than 10 liters of fluid in 24 hours. Sweat rate can reach 2 liters per hour during intense activity in warm weather.
Sweating is an efficient means of cooling the body when the humidity is low. When humidity rises, the evaporation of sweat decreases; no heat loss results from sweat that drips off or remains in clothing. Although pouring water over the head and neck may feel good, this practice does little to reduce body temperature because skin is usually already covered with sweat. Athletes must be encouraged to put more fluid in their stomachs than on their heads.
Sodium, chloride, and to a lesser extent, potassium and magnesium are lost in sweat. Salt tablets are not recommended without the supervision of a physician. The American diet provides more than enough sodium to replace losses.
Sodium rich foods include pizza, ham and potato chips.
Potassium rich foods include citrus fruits, juices, melon, strawberries, tomatoes, bananas, potatoes, meat and milk.
Dehydration (less than 2% of body weight) will impair performance and increase the risk of heat illness. Adequate food intake is essential to maintain normal hydration and prevent an abnormal rise in body temperature. The average adult requires around 2½ liters of fluid each day. The average athlete requires an additional 1 1/2 liters to 2 liters of fluid per hour of exercise. Therefore, athletes must conscientiously consume fluids before, during and after an event, or practice to ensure normal hydration. Since thirst is not a good indicator of dehydration, the athlete should be weighed before, during, and after training and competition. This will allow for more accurate determination of fluid loss. The athlete should ingest a fluid volume that is 125% of sweat loss (1 liter of sweat equals 1.25 liters of fluid intake).
Athletes should avoid consuming excessive protein, caffeine and alcohol because these substances will increase urine output, and result in further dehydration.
Heat Exposure Syndromes
- Heat cramps may be caused by excessive muscle fluid loss and electrolyte imbalance. Heat cramps usually occur in those who sweat profusely, usually before acclimating to hot weather and usually occurs in legs, arms and abdominal muscles.
- Heat exhaustion is next in severity with regard to heat exposure syndromes. It is caused by inadequate cardiovascular response to the circulatory stresses of heat exposure. Blood volume is insufficient to respond to demands of increased flow to skin, muscle and viscera. Peripheral vascular collapse (shock) occurs. Heat exhaustion can result from salt depletion or more commonly, water depletion. Symptoms will include weakness, headaches, nausea, vomiting and even unconsciousness.
- Heat stroke is the least common; however, it is the most serious heat illness. Heat stroke is failure of all of the body’s neurologic cooling mechanisms resulting in severe hyperpyrexia (body temperature greater than 105 degrees Fahrenheit or 41 degrees Celsius). Heat stroke is a true emergency with very high mortality. Heat stroke death can even occur at ambient temperatures as low as 70 degrees Fahrenheit. Treatment is immediate cooling by immersing the athlete in a bathtub filled with ice cooled water, wrapping with wet sheets or compresses, or cooling with fans during the transport to the hospital.
In part II, I will discuss some preventative measures and hydration protocols that is recommended for coaches, athletes and families.
For more information log on to www.drjabbour.com.
Dr Jabbour is the team physician and sports injury advisor to Cascia Hall High School, Tulsa Crude United States Hockey League and Oklahoma Region Volleyball Association.
Heat Exposure Syndromes and Fluid Replacement - Part II
Reducing Risks of Heat Stress
- Acclimatization describes the body’s physiologic adaptation to heat stress. It also describes the increased capacity to work in the heat. There is controversy if acclimatization occurs in days or months, most researchers believe that acclimatization occurs in 4 to 7 days with as little as 90 minutes of exposure to heat per day.
- Pre-season conditioning: Physically fit athletes require much less acclimatization in high heat and humidity then those who are not well conditioned.
- Coaching techniques can significantly lessen the risks of heat illness. Workouts in light weight, porous and light-colored clothing with short sleeves and short socks are usually recommended. Perspiration soaked uniforms should be changed during the practice session, and skin should be exposed to air and helmets removed as often as possible. Early morning or late afternoon practices are recommended when weather is not hot and humid. During practices in late a.m. or early p.m., players must be acclimatized to these conditions. Practices should be shorter and less intense with less clothing or uniforms and more frequent rests and fluid breaks in shaded and breezy areas. Athletes who have lost 2% of body weight should be excluded from practice.
- Fluid replacement: Unrestricted fluid intake during practices and games is encouraged. Ideally, the rate of fluid replacement should approximate rate of sweat loss, which can be checked with daily weighing. A well hydrated athlete can work longer, harder and more safely than one who is dehydrated.
- If a sports drink is not available, plain water is a good thirst quencher. However, ingesting water only will turn off the thirst mechanism prematurely, thus reducing voluntary fluid intact. Sports drinks are the preferred beverage when athletes are working hard and sweating profusely. The sweeteners and flavor of the sports drink may encourage voluntary fluid intake. The carbohydrate in the sports drinks supplies energy to active muscles and the electrolytes help maintain fluid intake and fluid retention.
- Replacement of sweat losses: If sweat losses are not replaced, body temperature rises, leading to exhaustion, heat stroke and perhaps, death. Sweat losses are tracked by decreases in body weight. One pint of sweat equals one pound of body weight. Fluid loss as little as 1% of body weight can cause body temperatures to rise. Fluid loss of 3% to 5% of body weight stresses the cardiovascular system and impairs the ability to dissipate heat. At 7% fluid loss, collapse is likely. Although athletes commonly dehydrate 2% to 6% during practice in the heat, this level of dehydration is both detrimental to performance and potentially dangerous.
- Monitoring hydration status: Athletes need to record nude dry body weights before and after practices. Each pound lost during practice represents 1 pint of fluid loss that must be replaced before the next practice. Indicators of dehydration, include dark, yellow urine, decreased urinary frequency, rapid resting heart rate and prolong muscle soreness.
The ultimate goal of fluid replacement in sports is to start exercises hydrated, drink plenty of fluid during exercise, and to re-hydrate before the next session. Two hours before activity, the athlete should consume at least one pint of fluid. Athletes should limit caffeine intake. Caffeine acts as a diuretic; thereby, causing more urine output than what has been taken in. During activity, athletes should be given time to drink fluids. They should start drinking before they are thirsty and should be reminded to continue to drink at regular intervals. Although cool water is an ideal fluid replacement, sports drinks can also be consumed. If athletes find flavored drinks more palatable then plain water, they may drink more. Sports drinks contain carbohydrates and water electrolytes. The sugar content is about 6% to 8%, which allows more rapid absorption of water.
After activity, total fluid intake should exceed 1 pint per pound to prepare the body for the next bout of exercises.
Summary of Fluid Replacement Guidelines
- Drink 16 ozs. of cool beverage 2 hours before work out.
- During activity, drink frequently 6 to 8 ozs. every 15 minutes.
- Provide cool beverages at 50 to 70 degrees Fahrenheit.
- Athletes need to be reminded to drink during activities (thirst is not a good indicator of dehydration).
- After work outs, replenish fluids at the rate of 1 pint for every pound lost. Weight should be back to normal prior to next work-out (weight loss early in the season is miss-identified as fat loss: fat loss does not occur this rapidly early in season).
- Cold water or cold sports drinks can be utilized.
Dr Jabbour is the team physician and sports injury advisor to Cascia Hall High School, Tulsa Crude United States Hockey League and The Oklahoma Region Volleyball Association.