Wilderness and Rescue Medicine 7th Edition Jeffrey Isaac, PA-C and David E. Johnson, MD

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Wilderness and Rescue Medicine

by reducing heat exposure and production, and by fluid replacement as needed. Although urine output and color are often mentioned as the best field indicators of fluid status, thirst is probably more reliable. Thirst almost always precedes sig- nificant volume depletion and is a good reminder to drink before you have a fluid problem. Heat Exhaustion Heat Exhaustion is the term for heat related ill- ness characterized by elevation of core body temp above 38ºC and abnormal performance of one or more organ systems without injury to the central nervous system. For field purposes, heat exhaus- tion is diminished performance due to heat stress. Heat exhaustion may also signal impending heat stroke. The heat exhausted patient is awake with normal mental status, but complains of nausea, headache, and weakness. The history may reveal inadequate time to acclimatize to a new environ- ment or increased work load. The patient may report low food and fluid intake and reduced urine output. Body core temperature is normal to slightly elevated. Fatigue is the primary problem and there may be some degree of dehydration. If addressed early this is not a serious problem, but it requires imme- diate treatment in the field. The progression of heal illness must be halted and reversed.

General Principles

Severe Hypothermia

No Chance of Survival: • Obvious lethal injury • The chest is frozen • The core temperature is below 10°C • Submerged underwater more than one hour • Airway packed with snow in prolonged avalanche burial Wilderness Perspective

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If an AED is available, we recommend one shock if prompted and one round of medications per protocol if the body core temperature is above 25°C. Rewarming efforts and CPR should be resumed, and a measurable increase in tempera- ture observed, before trying defibrillation and medications again. How long advanced level field resuscitation should continue is the subject of some debate and real field experience is very lim- ited. One hour is probably a generous maximum. Heat-Related Illness Because vital organs work best at a temperature around 37°C, the body conserves only as much heat as it needs to keep it at that temperature and gets rid of the rest. Your primary mechanism for heat dissipation is skin vasodilatation and sweat. When sweat evaporates, it absorbs a tremendous amount of heat energy from the skin surface. This is a very effective cooling system if there is enough blood and sweat to keep it going. The body con- stantly sacrifices fluid to maintain normal tem- perature in hot environments. Like cold response, heat response is a normal process. If heat dissipation is not overwhelmed by heat production and retention the body core temperature will remain within an acceptable range. Eventually, continued heat stress will result in diminished performance and less heat produc- tion, especially in people not acclimated to the conditions. It can take two weeks or more to fully acclimatize to a hot environment. Heat response carries the anticipated problems of heat exhaustion and heat stroke. It can be reversed

General Principles

Heat Exhaustion

Mechanism: • Fatigue from exertion and heat stress • May also involve volume depletion Signs and Symptoms: • Awake, normal mental status, subdued • Sweating, mildly elevated core temperature • Vital sign pattern normal or early compensated volume shock depending on fluid status

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Tr eatment of Heat Exhaustion The treatment is the same as for heat response, just more urgent. Move the patient into a cooler