Heat Related Illness

Heat related illnesses range from "heat exhaustion" which in its most severe form is called "heat stroke", "dehydration", and "hyponatremia (low blood sodium)." All are preventable requiring knowledge, preparation, and appropriate clothing and exertion when the temperature goes up. Usually seen with high level of activity.

Physiology:

• • Heat Exhaustion (Heat Stoke): Related to heat and a rise in body temperature. May be mild with sweating and thirst, to severe (heat stroke) in which high body temperature can have life threatening effect of the brain and body tissues. There is almost always a degree of dehydration.

  • Predisposing factors included: age (the young and older individuals), obesity, and certain medications such as Beta Blocker for the heart, antihistamines and anti-depressants.

  • Dehydration: Occurs when more water and salt (both) are lost then are replaced by intake. Normal loses through urinating, sweating and breathing amount to 1.5 to 3 liters per day. When exercising in heat, losses can reach 2 to 3 liters or more an hour.

  • Risks factors include: age (older individuals), underlying medical problems, and certain medications such as diuretic, anti-depressants, pain medication.

  • Hyponatremia (low blood sodium): This occurs during sweaty exercise when food has been eaten but mostly plain water has been drunk. A dilutional effect occurs in the blood, lower sodium. This can lead to edema (water flowing out of vessel), especially affecting brain tissue and causing symptoms.

Differential diagnosis: Heat illness and dehydration often occur together.

Treatment: It is difficult for most non-medically trained individual to distinguish heat exhaustion from dehydration, however, treatments in the field are somewhat similar. With hyponatriema the signs and the history of plain water intake and little salty foods make this differential easier.

*I suggest that individual with even mild symptoms that abate quickly still do not cycle home. Rather, send someone back to get a car and transport them to the parking lot to continue treatment and rest in a shady spot while you call their emergency number.

Prevention:

• • Exercise in the cool of the morning or late afternoon on hot humid days.

  • Limit your pace and difficulty of your route in heat and humidity.

  • Wear light-color clothing.

  • Drink sensible, using a sports drink and drinking and eating as you go. The new idea of waiting until you're thirsty to drink in order to prevent hyponatremia (low blood sodium) is not my choice. Rather I prefer to continually sip a sports drink and carry pretzel and sports bar in my back pocket. I consume no more the 21 ounces of fluid an hour (your stomach can't absorb more than that an hour) and continually eat.

  • Be cautious if you're at increased risk (over weight, underlying medical conditions, on certain medications, etc.).

  • Stop with the first signs of any symptoms above.

Addendum:

• 1. During training, weigh in before and after a workout and learn to adjust fluid intake to minimize weight loss. If weight loss does occur, re hydration after activity is critical; drink 20-24 ounces of fluid for every pound of weight loss (not all at once). Also, eat foods with a high water content (fruits & vegetables).

  2. Be cautious if only replacing with only water. In such cases drink only when you're thirsty so as not to dilute your sodium and become hyponatremic (low blood sodium).

  3. Remember, it takes time to get acclimated to the warm weather.

Heat Stroke

Cause: Inability of the body to cool the individual.

Symptoms:

• • Usually with high activity in hot conditions,

  • Stops sweating and hot to touch.

  • May be associated with headache, dizziness, confusion (altered LOC), exhaustion, seizure, loss of consciousness.

Treatment:

• Call 911

  • Treat as in heat exhaustion. Do not give anything by mouth unless patient is conscious and can swallow,

• .

References

• 1. Backcountry First Aid and Extended Care, Buck Tilton, MS, WEMT, 5th Ed., 2007, Falcon Guides, ISBN: 987-0-7627-4357-5  

  2. First Aid and Wilderness Medicine, Drs Jim Duff and Peter Gormly, 11 Ed, 2012, KHL Printing, ISBN: 978 1 85284 

  3. First Aid, CPR, and AED, Advanced, Alton L.Thygerson, et al., 6th Ed., 2012, American College of Emergency Physicians, ISBN: 978-1-4496-3505-3 

  4. Dehydration and Heat Stroke   John Hopkins Medicine

  5. Dehydration, Heat Stroke, or Hyponatremia? The Recognition, Treatment, and Prevention of Hyponatremia Caused by High Exercise Outdoor Activities.   Education Resources Information Center (ERIC,) sponsored by the Institute of Education Sciences of the United States Department of Education.

  6. HEAT STROKE IN SPORTS: CAUSES, PREVENTION AND TREATMENT   by E. Randy Eichner, M.D.Gatorade Sports Science Institute,

  7. Heatstroke   Mayo Clinic

  8. Hyponatremia   Mayo Clinic

  9. Hyponatremia: Low Sodium Levels   eHealthStar (evidence based health articles)