Risk Management Heat Stress
In May of 2005, at the end of a 7-mile training run, a female hotshot crewmember became disoriented and began to show signs of heat-related stress. Emergency services were summoned and she was transported to the regional medical center.
During the months before the fire season, the crewmember participated in daily runs as long as 4 miles. Two days before the training run, the crewmember drove 14 hours, rested overnight, and drove 4 more hours to her duty station. That afternoon and evening, she consumed 32 oz of water. The next morning she met with the crew for a 7-mile training run at an elevation of 5,200 ft when the temperature was 71 °F. She did not eat breakfast before the run, but she did consume another 32 oz of water.
After 6 miles of running with the crew, the female crewmember "began to sprint ahead of the group." When she returned to the base, she began to suffer from "tunnel vision," and couldn't find the barracks. An emergency medical technician trainee and another employee saw the crewmember in distress and went to her aid. They found her to be extremely disoriented and acting irrationally, trying to climb a fence to get to a creek. Her color was "bad" and her pupils were fixed. They called 9-1-1 and began first aid. The crewmember was transported to the regional hospital, stayed overnight, and was released the next day.
The firefighter was determined to be suffering from a classic case of a heat disorder. While she had consumed 32 oz of fluid and was physically able to participate in the training run, she was not properly acclimatized to the heat.
Were Other Factors Involved?When considering the causes of this incident, it would help to have additional information, such as blood measures (blood glucose, sodium), recent food intake, alcohol or drug use, medical issues, and so forth. In addition to heat stress, other factors that may have contributed to the difficulties she encountered include altitude, low blood glucose (hypoglycemia), water intoxication (hyponatremia), or a combination of other factors.
Heat Stress—The firefighter came from a moderately warm climate and the morning temperature was only 71 °F. She had been training before the season and the run wasn't that long. Bob Karwasky, an exercise physiologist with the Los Angeles County fire department, noted that the firefighter picked up her pace during the last mile, while performance usually declines with dehydration. (During the 1990s, a hotshot crewmember dropped out after 3 miles of a 4-mile run, wandered in the desert, and died from heat stroke.)
Altitude—The subject gained 2,000 ft in her trip from home to work. The elevation of the run would have a modest effect on performance, and some acclimatization would be required to minimize the effects of the elevation change. Yet the subject was able to increase her pace during the last mile.
Hypoglycemia—The brain uses glucose in the blood for fuel. Symptoms of low blood glucose include nervousness, faintness, confusion, inappropriate behavior, and visual disturbances (such as tunnel vision). Low blood glucose can lead to coma and seizures. The subject didn't eat on the morning of the run. Individuals prone to hypoglycemia should eat on a regular basis, especially before vigorous activity.
Hyponatremia—Excess water intake (water intoxication) can disturb the body's fluid-electrolyte balance and lead to an abnormally low level of plasma sodium (less than 135 mmoles/L). The risk is more pronounced during long-duration exertion in the heat, in events like marathons, triathlons, and prolonged hard work (such as wildland firefighting or military training). When excess water intake is combined with loss of sodium in sweat, the risk of hyponatremia grows (sodium loss for a participant in the Ironman triathlon could approach 1 gram per hour during a 12-hour event). A moderate decline in plasma sodium may cause gastrointestinal symptoms or nausea. A more pronounced drop may cause unusual fatigue, confusion, disorientation, a throbbing headache, vomiting, wheezy breathing, and swollen hands and feet. Seizures, coma, and death are possible if plasma sodium reaches very low levels (less than 120 mmoles/L).
Those at greatest risk are small, slower athletes; those who sweat a lot; and those who lose lots of salt, drink lots of water before and during an event, and fail to replace electrolytes, especially sodium. Twenty-six cases of hyponatremia were diagnosed during several San Diego marathons. The average finishing time for runners experiencing hyponatremia was 5 hours and 38 minutes, a relatively slow time. Nine U.S. Marine recruits experienced hyponatremia on the same day, drinking 10 to 22 qt of water over a few hours of exertion. All survived after emergency treatment (Military Medicine, 2002).
You can drink too much water!
See the Field Notes section for advice on avoiding hyponatremia and acclimatizing to heat. While we are on the subject of heat-related problems, let's consider another uncommon but serious condition, rhabdomyolysis.
RhabdomyolysisExertional (exercise-induced) rhabdomyolysis is most frequently reported in military personnel (0.3 to 3.0 percent) and in law enforcement and firefighting trainees (0.2 percent) during hot, humid conditions. Damage occurs to muscle membranes, allowing cellular components (such as creatine kinase, myoglobin, and potassium) to leak out. Rhabdomyolysis can lead to renal failure, irregular heartbeats, and even death. Risk factors include sedentary lifestyle, high ambient temperatures, and intense exercise. Military and fire department records indicate that the risk goes down as fitness improves (Physician and Sportsmedicine, 2004). Persons taking cholesterol-lowering statin drugs may be at a higher risk for rhabdomyolysis. See the Field Notes section for advice on avoiding this uncommon condition.
