heat+illnesses

clinical home > environmental toc =Heat illnesses = A naked person keeping still in a room at a temperature of 28C will neither gain nor lose heat.

If the temperature rises to between 28C and 32C heat loss takes place from the skin as a result of vasodilatation of blood vessels in the skin: this increases heat loss through radiation.

If the person exerts themselves (and therefore their muscle metabolism generates heat), or if the ambient temperature is above 32C, sweating is required to lose heat. Sweating provides a cooling mechanism by allowing evaporation of the fluid to occur.

**Heat exhaustion and heat stroke occur when the rate of heat loss is less than the rate of heat generation.** This is most likley to occur if: 1) very high ambient temperature 2) exertion taking place 3) impaired physiological compensation (e.g. drugs) 4) humidity high so sweat cannot evaporate

Presentation on heat exhaustion & heat stroke:

Heat exhaustion
Is the most commonly encountered form of heat illness May result from physical exertion in hot environment; cardiovascular system cannot meet combined requirements of muscular, visceral and thermoregulatory blood flow. – Increased demand for cardiac output – Reduced ECF volume <span style="color: #000000; display: block; font-family: Georgia,serif; font-size: 110%; text-align: left; vertical-align: baseline;">Usually both salt and water deplete

<span style="color: #000000; display: block; font-family: Georgia,serif; font-size: 110%; text-align: left; vertical-align: baseline;">Clinical features
<span style="color: #000000; display: block; font-family: Georgia,serif; font-size: 110%; text-align: left; vertical-align: baseline;">Body temperature may be normal: <39 even if collapse (orthostatic hypotension likely) <span style="color: #000000; display: block; font-family: Georgia,serif; font-size: 110%; text-align: left; vertical-align: baseline;">The skin is cool and clammy with sweat <span style="color: #000000; font-family: Georgia,serif; font-size: 110%;">There is **no organ damage** (though may be dysfunction through underperfusion) - in heat //stroke// there is organ damage <span style="font-family: Georgia,serif;">Normal conscious level and neuro examination

<span style="font-family: Verdana,Geneva,sans-serif;">Treatment
<span style="font-family: Georgia,serif;">1) Move casualty to coolest place available (use shade etc) <span style="font-family: Georgia,serif;">2) Remove restrictive clothing and any that will insulate and retard heat loss <span style="font-family: Georgia,serif;">3) Oral rehydration (unless a lot of vomiting) <span style="font-family: Georgia,serif;">4) Evaporative cooling and ice/cold packs on big vessels (neck, axillae, groin)

<span style="font-family: Verdana,Geneva,sans-serif;">Heat stroke

 * <span style="color: #ff0000; font-family: Georgia,serif; font-size: 120%;">Heat + neurological problem = heat stroke until proven otherwise **

<span style="color: #0000ff; font-family: Georgia,serif;">This is a clinical emergency. The mortality rate is high (80%) unless the casualty gets the correct treatment promptly.

<span style="font-family: Verdana,Geneva,sans-serif;">Clinical features
<span style="font-family: Georgia,serif;">1) Temp above 40.5 <span style="font-family: Georgia,serif;">2) Abnormal neurology <span style="font-family: Georgia,serif;">3) Sweating //may// be absent

<span style="font-family: Verdana,Geneva,sans-serif;">Treatment
<span style="font-family: Georgia,serif;">1) RAPID cooling - use knowledge of mechanisms of heat loss from hypothermia to cause heat loss in casualty - method will depend on setting and resources. Immersion may be considered (used by US marine corps) <span style="font-family: Georgia,serif;">2) Avoid oral fluids because swallow may not be safe - give slow IV saline (which should be cooler than the casualty). 1 litre often adequate. <span style="font-family: Georgia,serif;">3) Treat seizures aggressively (they will cause temp to rise further <span style="font-family: Georgia,serif;">4) Suppress shivering with chlorpromazine (shivering generates heat so is undesirable) <span style="font-family: Georgia,serif;">5) Evacate urgently <span style="font-family: Georgia,serif;">6) Monitor core temperature if possible - avoid causing hypothermia; stop sooling when temp between 38 and 39 <span style="font-family: Georgia,serif;">7) Avoid using antipyretics - there may be liver or clotting dysfunction already and these may aggravate those

<span style="font-family: Verdana,Geneva,sans-serif;">video clip about an episode of heat stroke (at end click link to go to part 2)
media type="youtube" key="BiR5PwesF9M?version=3" height="390" width="480"

<span style="font-family: Verdana,Geneva,sans-serif;">link
<span style="font-family: Georgia,serif;">[|emedicine site on heat stroke] <span style="font-family: Georgia,serif;">[|a tragic case of exertional heat stroke] <span style="font-family: Georgia,serif;">[|physical exercise in the heat] <span style="font-family: Georgia,serif;">[|pathophysiology of heat stroke] <span style="font-family: Georgia,serif;">[|prevention of heat illness] <span style="font-family: Georgia,serif;">[|military operations in the heat]

<span style="font-family: Verdana,Geneva,sans-serif;">reading
The chapter on the Marathon des Sables in Mike Stroud's book "Survival of the Fittest" contains a chilling (no pun intended) account of heat stroke (p118)