The “dog days of summer” are certainly upon us again and incidence of both heat exhaustion and heat stroke are rising. It is important to know the difference between these two heat related illnesses and how to prevent and treat them in the field before one gets to a medical facility.
Heat exhaustion and heat stroke are not distinct illnesses, but instead they are diseases on a continuum. In most cases, exhaustion progresses to stroke if not recognized and treated. However, stroke can be the presenting problem and, due to its degree of severity, it must be recognized and treated aggressively. So, it is important to understand the differences between the two conditions. Before those differences are outlined, it is important to review how the body handles excessive heat. We are built with mechanisms to help us respond to excessive heat. The process of radiation, or transferring heat from the body to a cooler environment, accounts for the greatest degree of heat balance (about 65%), but only works when the body is warmer than the surrounding environment. Sweating contributes another 30%, through the evaporation of the sweat on our skin. If the sweat drips off the body, it does not cool us and only serves to increase the chances of dehydration. These mechanisms are affected by many factors, including age, disease, and medications. Both the old and the young do not have the ability to maximize the processes in the body that assist with radiant heat loss. Certain diseases, such as cardiac and thyroid diseases, also interfere with this method of temperature balance. Both prescription medications and illegal street drugs can also interfere in radiant heat loss and sweating. All of this shows us that it is quite easy to find oneself in a situation of heat illness.
Heat exhaustion presents with flu-like symptoms, including headache, vomiting, muscle cramps and lack of appetite. The individual with heat exhaustion is still sweating and their temperature may be normal, but is almost always less than 106 degrees Fahrenheit. Heat stroke will have the same flu-like presentation and sweating may or may not be present. The key important difference is the presence of central nervous system (CNS or brain) dysfunction. Those with heat stroke may be confused, delirious, unable to walk, have seizures or be comatose. It is this CNS abnormality that must be recognized as soon as possible, so that appropriate treatment can be instituted. Those with heat exhaustion should be allowed to rest in a cool spot, given fluids, given foods with glucose and general supportive care. Those with stroke need aggressive pre-hospital treatment. Their clothes should be removed and their skin sprayed with liquid and fanned to promote heat loss. If available, ice bags should be placed on areas where large blood vessels come near the skin surface (neck, axilla, groin, scalp). They should not be given anything orally, due to the CNS dysfunction. Lastly, if you are the person in charge of the backcountry group where an individual has heat stroke, you should call for medical evacuation due to the seriousness of this condition.
Like many other illnesses, the phrase “an ounce of prevention is worth a pound of cure” applies in this situation. Most of us know how to prevent heat illness: Drink lots of fluid, wear heat dissipating clothing, avoid the sun when possible, avoid hard work or exercise in the heat of the day. But, when those avoidance techniques fail, knowing the difference between heat exhaustion and stroke can save a life. And back to those “dog days of summer”: it turns out that phrase has nothing to do with sultry hot days. This was a phrase the Greeks and Romans used regarding the position of the dog star, Sirius, in the summer sky. The “dog days” occurred around the day when Sirius appeared to rise just before the sun, in late July. They referred to these days as the hottest time of the year, a period that could bring fever, or even catastrophe. Heat illness can occur at any time of the year, but certainly the phrase lives on in our culture.