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Summer in the City!

Summer is Upon Us..

You know the usual precautions: drink lots of water, wear light colored loose fitting clothing, seek out shade, and don’t exercise outdoors when it is extremely hot and humid. What you may not know is the physiology behind heat illness, which can help you understand certain drugs and medical conditions that can make someone more susceptible to heat illness.

What is Heat Illness?

Our bodies gain heat from our internal energy processes, and also from the environment: the sun’s rays, sitting on hot sand on the beach, or a hot wind blowing on you. When the total heat your body experiences exceeds what you need to remain at 98.6 degrees internally, corrective mechanisms start to work to shed the excess heat.  Blood vessels in your kidneys and GI tract shut down, your heart rate increases, and blood gets shunted to your skin where the vessels enlarge (you look “flushed”) and heat can now radiate out through the increased skin flow, (just like the sun radiated heat in).  Your brain decreases your internal heat production, and you also start to sweat. Sweating, wherein liquid sweat is evaporated, is a phase change (liquid to gas--remember high school chemistry?) that efficiently carries heat away from your body.

Like any defense mechanism, this only works up to a point. When these protections are overwhelmed by incoming heat, symptoms start to occur.  It is important that you react properly so that the things don’t get worse. Remove the person from direct sunlight, loosen restrictive clothing, and begin cooling as soon as possible. In order of severity, heat illnesses are categorized as follows:

  • Heat cramps: your sweat is salty; if you drink only plain water to rehydrate, you are not replacing the salt, and the salt content in your muscles drops. This causes involuntary contraction, or cramps, usually in a calf, on one side. Drinking water with about ¼ teaspoon of salt per liter will cure this. Use salt tablets if exercising in extreme heat. IV saline also works.
  • Heat syncope: this is fainting from loss of fluids that are not being replaced adequately, coupled with the blood “pooling” in your lower extremities due to the dilation of your veins (which are trying to help shed heat).  The leads to low blood flow to your brain, causing the “faint”. Usually IV fluids and/or spraying on cool water and fanning a patient (which causes effective heat transfer through evaporation) can be curative. Cool compresses may also be used. Thus, both heat syncope and heat cramps may be candidates for urgent care center treatment. 
  • Heat Exhaustion: this is a worsening of the symptoms of fluid loss. Your blood pressure drops, and your central body temperature starts to rise.  You are about to be in big trouble.
  • Heat Stroke: at this point, your brain starts to decompensate. You might be confused, or seize, or slip into a coma.  Without proper care, death comes quickly. Both heat exhaustion and heat stroke require emergency department transfer via EMS.

Who Can be Affected By Heat Illness?

Everyone! However, cardiac patients and the elderly are at higher risk (they can’t increase their heart rates to help shed heat), as are patients on beta blockers, (which also prevent heart rates from going up). Alcohol and fluid pills cause worsening fluid loss, and cocaine and other stimulants increase your internal heat production, all of which make heat exposure riskier.


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