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

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Wilderness and Rescue Medicine

Evaporation refers to the heat energy absorbed by water as it turns into water vapor. The body uses this very efficient mechanism for cooling in the form of sweat. Water evaporating from the skin will cool your patient very efficiently whether he needs it or not. Radiant heat energy is emitted and absorbed by all objects, including your patient. This is long- wave electromagnetic radiation well below the fre- quency of visible light. This energy is the warmth you feel from sunlight or a campfire. Radiant heat from your body can be absorbed by dense or thick clothing or reflected to you by a foil covering.

a cup of hot tea is minimal compared to the heat that is produced when the patient burns the four tablespoons of honey you put into the tea. Do not delay food and fluids while waiting for your stove to heat up. Most of the time, your rewarming efforts will be successful. Sometimes, the system fails or is over- whelmed by environmental conditions, resulting in a drop in body core temperature. Shell/core compensation persists, shivering continues, and your patient’s mental status begins to decay. Your anticipated problem has become the existing problem. Mild Hypothermia

General Principles

Transfer of Heat Energy

General Principles

Conduction: by direct contact Convection: by wind or moving water Radiation: by long-wave energy Evaporation: by water absorbing energy as it evaporates from skin

Mild Hypothermia

Mechanism : • Heat loss exceeds heat production. • Onset can be acute or sub-acute. Signs and Symptoms: • Early brain failure with mild to moderate mental status changes • Shivering • Shell/core effect • Core temp 35-32°C

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Noncompressible insulation such as a closed- cell foam pad should be used to protect the patient from conductive heat loss to the ground or other cold objects. High-loft, low-density insulation such as a synthetic or down sleeping bag forms a dead air space around the patient, reducing con- vective heat loss and trapping the radiant heat being emitted by the patient. A waterproof vapor barrier around the insula- tion prevents wetting of the package from rain or snow and reduces the evaporative cooling from moisture already on the patient. Support for heat production is equally criti- cal. Your patient needs calories and fluids to fuel shivering. Simple sugars are best at first. They are absorbed and converted into energy quickly. Complex carbohydrates, fats, and protein can be added later to maintain heat production. Adding heat in the form of warm liquids or heat packs is comforting, but not as useful as the calo- ries, hydration, and exercise. The heat energy in

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Rescuers will certainly think of hypothermia in cases of obvious and extreme exposure such as cold-water immersion. Even dressed for cold weather, ice water can kill you within an hour or two. Nobody will miss the diagnosis in situations like this. In most backcountry situations, however, the onset of hypothermia is more often insidious than dramatic. It progresses slowly and quietly in a patient who is just a little cold for a long time. In this case, the problem is easy to overlook. Hypothermia may be the primary problem you are treating or a side effect of environmental con- ditions. It is a common complication in trauma cases in which a patient has remained immobile for hours while waiting for evacuation. It also develops in rescue team members waiting hours for instructions.