You may be thinking, Scott, its April why are you talking about heat, its COLD where I am, and I just wanted to get ahead of this unusually mild winter and expected extreme summer, besides I always enjoy the clinical aspects of treating environmental emergencies, whether it is a cold issue, or a heat related emergency, all offer challenges and diagnostic difficulties. In this article, I will attempt to refresh your memory on the most common heat related illnesses presented to the prehospital provider.

We know that humans are warm blooded creatures and that our survival depends on our body’s ability to maintain a core temperature of between 97° F (36.1° C) and 99.5° F (37.5° C). Our body can maintain our core temperature in some very extreme circumstances, we can survive, unclothed in temperatures from 55° F to 130° F with our core temperature only varying 1 to 2 degrees F.

Let’s look at some physiology, heat is the kinetic energy of molecules in motion, and it is this heat production that helps us control our core temperature. Heat is produced by many of our natural bodily functions, and this is known as our Metabolic Rate. When at rest this is known as our Basilar Metabolic Rate. Heat production can also be enhanced with physical activity, muscle fibers generate heat when working out or shivering when the loss of the body’s heat is greater than its production. Our blood and blood vessels play an important part in regulating our thermodynamics. Blood and blood vessels transport our excess core heat to the skin through an increased chronotropic effect and become vasodilated so that heat loss can occur. Our skin and subcutaneous tissue also play an important role in keeping heat in, the skin will constrict blood vessels and decrease the amount of heat lost to the outside, our subcutaneous tissues act an insulator, and the erector pillar muscles stand up our body hair trapping an insulating layer of air to add to our insulation.

How do we get rid of our excess heat? There are four ways we lose heat: conduction, radiation, convection, and evaporation. When we generate too much heat, we must lose the excess quickly to avoid overheating. Convection is one of my favorites, there is nothing like sitting on your porch and feeling the cooling breeze pass you buy, that in a nutshell is convection, as air currents pass over a warmer object, they pull heat with it. Which brings us to evaporation, as liquid is transformed into a gas it takes heat with it. We normally loose approximately 600ml of body fluids just through normal breathing and evaporation alone! However, as the surrounding environmental humidity increases the efficiency of evaporation decreases.  Then, there is radiation, all living things radiate heat through infrared rays to the environment. In a normal temperate room, the body can loose up to 60% of its total body heat by radiation alone. Finally, there is conduction, or the transference of heat through a gradient of warmer to cooler.

Clinical findings:

Let’s first look at a fever, sure you might think that this is a normal finding in someone with an infection, but this is also a hyperthermic event. The body produces excess heat in the attempt to kill invading viruses, and bacteria. As we know the hypothalamus controls our internal thermometer and has a set point for temperature. Many things can reset this internal thermostat, things such as infection, brain tumors or bleeding in the brain that compress the hypothalamus. When this occurs, it takes several hours for the body to catch up with the new set point. Signs and symptoms can include chills, chattering teeth and the patient complaining of being extremely cold. These effects occur due to the fact that the blood temperature is lower than the set point.

With can classify heat related injuries into five categories.  First, we have heat cramps. This relatively minor condition usually occurs when workers and athletes are functioning in a hot environment and develop an electrolyte imbalance. This is usually treated with rest and rehydration with an electrolyte solution such as Gatorade. Heat Tetany is usually seen when patients are in an extremely hot environment and hyperventilate to help evaporation, an example would be a dog panting. When you hyperventilate you blow down your Co2 which puts you into a state of respiratory alkalosis, causing numbness, tingling, and carpopedal spasms. Treatment is usually related to slowing down the respirations and removing the person to a cooler environment with rehydration. Heat exhaustion is a severe condition requiring rapid intervention. This condition presents with dizziness, headaches, irritability, nausea and vomiting but the patient is usually still sweating. This condition is frequently seen in fire fighters that are wearing heavy turn out gear and are not resting and rehydrating while working. Body temperatures usually range from 102°F to 104°F. Treatment includes removal from the hot environment, rehydration, and rest. Heat syncope is the fourth in our heat related conditions, usually resulting in a postural hypotension. This is due to the body undergoing widespread peripheral vasodilation in an effort to cool down its core. Usually seen with dehydration, treatment is easy: manage the fluid and remove to a cool environment. Finally, the most serious heat related condition is heat stroke. This condition presents with the lack of sweating, a core temperature of over 104.9° F, and altered mental status. This is a true emergency! Treatment includes rapid cooling to a target body temperature of 104° F in either a cool bath, or ice water. Care must be taken not to rapidly cool the patient down below the target temperature as shivering and vasoconstriction may occur causing a rebound hyperthermic event. We would also treat all of the signs and symptoms encountered; whether they necessitate CPR, IV fluids, or medications we would follow the local protocols and treat accordingly.

So, in conclusion, keep cool, drink plenty of water to stay hydrated and if working in a hot environment take a break, your health may depend upon it.

References

Bledsoe BE, ET al Paramedic

Care: Principals and practices, Vol 3: Medical Emergencies. Brady/Pearson Education: Uppersaddle River, NJ