Heat Exhaustion And Exertional Heat Stroke
It is well known that training and competing in the heat can have harmful effects to your health and performance. Everyone knows to stay well hydrated and that acclimatizing to the heat is beneficial, but it has occurred to me that many riders, parents and staff don’t actually understand how heat injuries occur and what to do about them if they happen. In the interest of safety first and performance second, the purpose of this article is to explain what takes place in the body to cause heat exhaustion and exertional heat stroke and the most effective on site treatment for these possibly catastrophic heat injuries.
Think of heat exhaustion and exertional heat stroke (EHS) as a continuum of exercise and heat related injury. Heat exhaustion is first and simply means that you have to stop riding or exercising; your body is just too exhausted and cannot continue to do the work required in the heat. Heat exhaustion can usually be treated with body cooling and fluid replacement. The athlete typically recovers on site without hospitalization and further complications are rare. Think of heat exhaustion as your body’s way of preventing you from injuring yourself further.
Heat exhaustion is mainly caused by dehydration. The rising core temperature of your body during exercise in the heat causes profuse sweating as your body attempts to combat this through evaporative cooling. The latest research indicates that this causes central fatigue, which is basically fatigue of your brain and central nervous system. Central fatigue causes the muscles in the blood vessels to relax and lose tone (called vasodilation). Vasodilation increases the total volume of the circulatory system, which is a closed system, so the pressure drops. The resulting cardiac inefficiency leads to a cascade of negative events: less blood flow removing heat from the working muscles, less blood flow bringing oxygen and fuel to the muscles and less blood supply to the brain. Combined with the increased energy cost of working in the heat (especially in those not acclimatized), exhaustion and even collapse follows.
Symptoms of heat exhaustion are not too specific: low blood pressure, high heart and breathing rate and the rider appears sweaty, pale and ashen. Other symptoms include: headache, weakness, dizziness, “heat sensations” on the head or neck, chills, goose bumps, nausea, vomiting, diarrhea, irritability and loss of muscle coordination. Muscle cramps may or may not accompany heat exhaustion.
Riders suffering from heat exhaustion should immediately be moved to a shaded or an air conditioned area. All gear and excess clothing should be removed and the athlete should lay down with his or her legs elevated. Heart rate, breathing rate, rectal temperature and nervous system symptoms should be monitored. Cooling therapy can aid in more quickly returning the athlete to a normal state (see treatment for EHS). Hospitalization and medical supervision are necessary for IV fluid intervention if the heat exhaustion is severe or the athlete cannot keep fluids down, has diarrhea, or symptoms do not improve with the treatments listed.
Next on the severity scale is exertional heat stroke. EHS requires immediate treatment and if not reversed quickly, can cause organ damage, organ failure and death. EHS is caused by elevated body core temperature and is clinically defined by a core temperature of 40°C/104°F. The massive heat produced by working muscles, outside temperature/humidity and other factors overpowers the body’s cooling mechanisms and core temperature rises faster than it can be reduced. Upon reaching a critical level (around 40°C), a catastrophic chain of events can occur. At this temperature, the cell membranes become damaged and cell energy systems cease to work correctly. This leads to collapse of major cell structures and functions. You can apply the simple logic from here: since every organ and tissue in your body is made up of cells; brain, cardiac, renal, gastrointestinal and muscle systems can fail and this cascade of bodily collapse can cause death.
Symptoms of EHS include: disorientation, confusion, dizziness, irrational or unusual behavior, inappropriate comments, irritability, headache, inability to walk, loss of balance and muscle function resulting in collapse, profound fatigue, hyperventilation, vomiting, diarrhea, delirium, seizures, or coma. Beware: EHS symptoms are often confused with concussion symptoms. Also note that EHS victims almost always have sweat soaked, pale skin at the time of collapse. Classic heat stroke (non-exercise related) victims usually have dry, hot and flushed skin. This is a common misdiagnosis – being sweat soaked DOES NOT rule out EHS. Also note that an athlete can suffer from EHS without passing through heat exhaustion first; it is rare but it can happen. Immediate recognition of EHS symptoms is critical for survival; a rectal temperature should be taken in anyone who collapses or shows signs of EHS and immediate care should be given to anyone above or near 40°C.
Immediate whole body cooling is critical for survival in EHS victims. The mortality rate is directly related to how much time the core temperature remains above 40.5°C and how quickly it can be brought down below this temperature. The cooling needs to be done IMMEDIATELY and ON SITE. Do not wait to transport the victim to a medical facility, begin cooling as soon as you suspect EHS! The absolute quickest way to reduce core temperature is a total body immersion in an ice water or cold-water bath. This treatment has the lowest mortality rates. The next best solution is to rotate towels soaked in ice water as they are applied to the head, trunk and limbs while ice bags are applied to the neck, armpits and groin. The least effective treatment is ice bags only on the neck, armpits and groin. IMMEDIATE BODY COOLING is critical for survival. Again, do it without hesitation and keep doing it until rectal temperatures drop below 40.5°C and nervous system functions return to normal, signaling you are out of the death zone. If you know you will be training or competing in an environment that can lead to EHS, keep ice and a suitable container to be used as an immersion tank nearby! Again, this is a life-threatening situation; know the signs, know how to treat, and BE PREPARED!
This past summer has produced especially brutal conditions for both training and racing. A few weeks ago at Red Bud, the motocross community regrettably lost a member due to suspected EHS and undoubtedly more riders and athletes have suffered heat injuries this summer. Heat exhaustion is very common during the summer months; I had a client suffer from it a few weeks ago here at my own track and luckily it wasn’t serious. Please arm yourself with the knowledge to recognize both heat exhaustion and EHS, do more research on your own, and be prepared!
References
Armstrong, Lawrence E., Douglas J. Casa, Mindy Millard-Stafford, Daniel S. Moran, and Scott W. Pyne. “Exertional Heat Illness during Training and Competition.” Medicine & Science in Sports & Exercise 39.3 Mar. (2007): 556-72. Web. 29 July 2011.
Originally published on Vurbmoto.com