Heat disorders and the athlete

Heat illness is one of the most common causes of disability in sport. The consequences of a major heat related disorder can be catastrophic. The approach to prevention and care of heat illness has changed greatly in the last 15-20 years.

The AFCA documented 39 deaths from heat illness in the years 1964-1973. However, in the decade from 1974-1984 there were only 15 reported fatalities from heat. The reasons for this decline are many; education of coaches and trainers, free availability of water during practices, clothing changes, and a more complete understanding of the water-electrolyte cycle in the body.

The average adult male has 60 % of his body weight in water. The body requires an approximate intake of 2300 ml [ 2.4 qts ] of water per day. He will eliminate approx. 1100 ml in the urine, and 900 - 1200 ml through the skin and lungs.

Certain changes take place in the cardiovascular system in response to increased heat stress. Increase in the cutaneous venous volume. This enhances the heat loss from the skin but hampers the effective central blood volume.

A fall in blood pressure is avoided because of a reduction in the renal and splanchnic [visceral] blood flow. This physiological change accounts for the complications involving the kidneys, liver, and other organs in severe heat illness cases.

Depending on how long the body is subjected to the high levels of increased core temperatures, coupled with the changes in the CV system, this system will begin to fail.

The more acclimatized and conditioned and athlete, the greater his/her percentile of water to body weight. This is how the body fights the possibility of fluid dehydration.

Salt depletion can also become a problem in the person subjected to heat stress. Because of low dietary NaCl, & high losses of NaCl due to fluid loss, the level of extracellular fluid is reduced as well as cardiac output and blood pressure. This condition is not characterized by thirst or relieved by ingesting salt free fluids, it can only be treated with IV fluids or the ingestion of a 10% saline solution.

Water dehydration is characterized by thirst and oliguria. This condition can be relieved by the ingestion of water. Water depletion with a normal decline in the total body water does not produce peripheral vascular collapse because the plasma volume contributes only 1\12 of the total fluid deficit. Water depletion is more common than salt depletion, however, differentiating between the two can be difficult because their symptoms are so closely matched.

The athlete that is acclimatized may loose 3.5 ml of water per hour. This rate of loss over a 3-4 hour period may account for 4-6 % of the athletes total body weight. The athlete may require 4000 ml plus of fluid intake to replace what is lost during practice or competition.

The healthy acclimated person may have 10 grms \ NaCl per liter. The person with heat exhaustion may still have 6 grm per liter. The patient will conserve salt by decreasing urinary excretion. The patient with heat cramps will also not show dramatic changes in their serum sodium levels.

The fluids that are consumed should be cold with sodium concentrations under 9.5 meq [ 218 mg,] 9.5 meq [ 337 mg ] of chloride, and 4.7 meq [ 183 mg ] of potassium. The sugar [ free sucrose and glucose ] levels in a " sport drink " should not exceed 8 %. levels over this have shown to increase the gastric emptying times. [ ACSM position statement ]. there is some recent research dealing with glucose polymers and their providing energy through a drink without significantly delaying the stomach emptying time. This author feels that more research is needed. The use of an electrolyte solution for the locker room for the purposes of prehydration and the continuation of freely attainable fluids is critical for fighting the heat illness problem.

The emphasis on emptying time is important because very little water is absorbed through the stomach. The majority of fluid is absorbed in the intestine. Cold fluids empty faster than do warm or luke warm ones. The myth that cold fluids causes gastric distress are unfounded, gastric distress is caused by the volume of fluid consumed.

The cellular changes that occur from heat illness must be understood to better combat the problem. The osmolarity or the regulation of the water balance is controlled by the ADH hormone. [antidiuretic hormone] The sodium level is maintained by aldosterone. A substance found in the adrenal cortex.

Extracellular changes include increasing the permeability of the cell to the sodium ions and the stimulation of the sodium pump, however, this further depletes the energy level of the cell. The sodium pump increases the intracellular acidity which stimulates the Na+, -h exchange. It increases the extracellular sodium and thus membrane permeability. It increases the frequency of neural stimulation which increases the sodium-potassium flux across the nerves.

Potassium is responsible for the ICF ion levels, the regulation of intracellular osmolarity, promotes nerve impulses, muscle function, and heart muscle function. It moves out of the cell under conditions of heavy work or exercise.

The body tends to conserve NA+ at the expense of losing K+. Losses of k+ are often increased by diarrhea, vomiting, and poor dietary replacement.

Calcium maintenance depends upon the proper intake if dietary calcium, the availability of Vitamin D and the level of blood phosphorus. Changes is the levels of calcium in the body are noted with increased nerve irritability, decreased blood clotting times, and changes in membrane permeability.[loss increases the permeability]

Magnesium also is an important electrolyte with functions of maintaining nerve irritability, carbohydrate metabolism, and helps in the regulation of blood phosphorus.

Heat illnesses can be divided into 4 types, they are in order of occurrence:

Heat cramps, Heat syncope [ fainting or weakness ], Heat exhaustion, and Heat stroke.

Rest, ice packs to the affected muscle, application of mild counter pressure to the affected group and fluid replacement. If cramping symptoms persist, then replacement of fluids via IV administration may be needed.

Many people may think that it is the under conditioned and non acclimated athlete that cramps in the early season. While this may be true in some cases, the majority of elite athletes that cramp due so because they are low in body fat, (thus reducing their extra fluid stores) and highly conditioned, (thus increasing their muscle efficiency and increasing their heat output). These athletes lose fluid faster than non acclimated athletes because their bodies are accustomed to the extra cooling needs.

Weakness, tiredness, dizziness, faintness, weak-rapid pulse, decreased blood pressure.

Stopping activity, remove the athlete from direct sunlight, application of cold towels, water replacement, and using a fan to help cool the patient.*

Extreme weakness, pale faced, profuse sweating, slightly elevated body temperature [ may be normal ] thirst, oliguria [ reduced frequency of urination ], delirium, and unconsciousness

Cool the body, fluid replacement, electrolyte replacement, remove from sun and outside heat. Possible intravenous fluid replacement. Extended rest. Use fans to help cool the body. The heat exhaustion patient may require hospitalization.

Faintness, exhaustion, staggering, headache, nausea, possible unconsciousness, elevated body temperature, strong rapid pulse with low blood pressure, hot dry skin.

[ recent literature, Phys. and Sports Med. 6\89, suggests that the temperature for the water in the case of total body immersion should be between 60-70 degrees. This does not cause shivering or drive the temperature higher in an attempt to heat the body, if ice baths are to be used, there must be attendants to constantly massage the body. There is also some discussion as to using niacin to dilate the capillaries. Valium is also by some physicians to control the shivering and muscle spasms.]

The athletic trainer should have their athletes weigh in before every practice and weigh out after every practice. This must be a team requirement.

If the athlete losses more than 5% of their total body weight over the course of the days practice, he / she should be held out until that weight returns.

Beware of the athlete that losses 1 or 2 lbs each day. This athlete is slowly becoming dehydrated and will be a problem in the 3rd or 4th day of practice.

Encourage pre-hydrating by drinking 32oz. Of fluids before practice and games. The athlete should consume approx. 16 oz. Every 30 minutes of activity. The use of Gatorade will replace needed electrolytes and supplement some carbohydrates for needed caloric input during sustained physical activities.

Watch suspected players carefully, remove shoulder pads and helmets for conditioning. Give unrestricted water.

Restrict practice, add additional water breaks, reduce or eliminate conditioning

When the dry bulb temperature and the wet bulb temperature add up to 150 or more, your athletes are exposed to a higher risk for heat illness.

3. Allow your athletes time to become acclimated to the heat this may take 7-12 days. Encourage them to work in the heat and do some fitness related activity during the summer.

7. Stress prehydration to your athletes. Athletes will drink only to satisfy their thirst, not to replace fluid loss. Pre hydration with Gatorade and Rehdralyte (Ross Labs) has proven very beneficial to our athletic population.

Located outside of the Walsh Sports Medicine Complex
the "Gatorade" bar provides athletes with Gatorade,
Water and GatorLode for carbohydrate replenishment.

8. Restrict soft drinks and iced tea during heat stress time of the year, they can lead to increased urination and slowed gastric emptying times.

11. Know what medications your athletes are taking. Some can dehydrate the body.

The time required for rehydration may range from 12 to 48 plus hours depending upon the degree of dehydration.