Hypothermia

Thermoregulation & Cold Physiology

Hypothermia occurs when a person cannot maintain their normal body temperature in the face of a cold challenge. The cold challenge increases as a person is exposed to progressively decreasing temperature, increasing humidity, and increasing wind. People respond to a cold challenge by increasing their heat production through shivering and maintaining their core temperature through peripheral vasoconstriction. Heat production requires an efficient metabolism and accessible calories. The ability to produce heat via shivering or exercise drops as their available calories become depleted. Fitness, hydration, health, and injury all affect a person’s metabolism and their ability to produce heat.

The onset of hypothermia is variable and depends on the severity of the cold challenge, the length of exposure, and the health of the patient. Acute hypothermia may occur in minutes to hours with cold water immersion regardless of the victim’s health. Subacute hypothermia may occur in hours to days in a mountain or river environment where decreased calories predispose the climber, hiker, or paddler to hypothermia from a moderate cold challenge. Expedition members with predisposing factors (poor health, inadequate nutrition, poor hydration, etc.) can develop a chronic cold response during prolonged exposure (days to weeks) to cool environmental conditions due to limited caloric intake and no glycogen or fat stores. They may easily become hypothermic when presented with a slight increase in the cold challenge.

Notes:

• Someone under your care should never get colder 94 degrees F.
• The heart is electrically unstable below 90º F and prone to cardiac arrest.
• Below 86º F Check pulse for 60 seconds; if not present, recheck after 3 minutes of rescue breathing.
• If a hypothermia thermometer is not available, treat all V, P, U patients as moderately or severely hypothermic.

Cold Response Treatment
Shelter, Insulation & Heat

• Remove wet clothes.
• Add insulating layers.
• Seek shelter.
• Use a solo hypothermia package if patient needs transportation.
• Use a hypothermia package with three people, three bags, and three pads if patient is to remain in camp.
• Add heat packs to patient's core and extremities (hot water in hydro packs).

Food & Water

• Give the patient food to replace lost calories. Begin with simple sugars and carbohydrates; add protein and fats later.
• Give the patient warm water and electrolytes to replace fluid loss via cold diuresis.

Rest vs. Exercise

• If their caloric stores are low and patient has been exercising, require them to rest.
• If they have been immobile in a cold environment (e.g., belaying, sitting in a raft, etc.) and their calories are intact, encourage them to exercise.

Evacuation

• An evacuation may or may NOT be necessary. Reassess cold challenge, route, supplies, equipment and experience in light of the recent incident and consider a Level 3 Evacuation.

Mild Hypothermia Treatment
General

• Treat as per cold response until patient is awake, alert, and warm with intact judgment.

Evacuation

• An evacuation may not be necessary if re-warming is successful and patient is awake, alert, and warm with intact judgment.
• Reassess cold challenge, route, supplies, equipment, & experience in light of the recent incident and consider a Level 3 Evacuation.
• If re-warming is NOT possible or unsuccessful, begin a Level 1 Evacuation.

Moderate Hypothermia Treatment
General

• The heart is electrically unstable below 90 ℉ and prone to cardiac arrest.
• Handle with extreme care to avoid triggering accidental V-fib (cardiac arrest).
• No food or water by mouth.
• No exercise to avoid triggering accidental V-fib (cardiac arrest). Exercise returns cold acidic blood to the core rapidly and catastrophically dropping the core temperature and upsetting the electrical conductivity of the myocardium.
• No rapid external re-warming to avoid triggering accidental cardiac arrest. Rapid external re-warming — hot tub, sauna, etc. — initiates extreme peripheral vasodilation and a subsequent drop in blood pressure that precipitates V-fib.
• Use a solo hypothermia package if transporting or three-person hypothermia package if in camp.

Evacuation

• If re-warming is successful and patient is awake, alert, and warm with judgment intact, begin a Level 3 Evacuation.
• For all other patients begin a gentle Level 1 Evacuation in a solo hypothermia package.

Severe Hypothermia Treatment
General

• Treat as per moderate hypothermia. Complete field re-warming is highly unlikely.
• Assist patient’s breathing (PPV) if P or U when possible.
• No chest compressions if cardiac function is suspected.
• Advanced Life Support drugs and defibrillation are typically ineffective below 86º F. If the patient’s core temperature cannot be determined or is above 86º F (30º C), follow the AED protocols for a normothermic patient. If the patient’s core temperature is below 86º F (30º C) and the device states that shocks are indicated, shock the patient once. If unsuccessful, discontinue use of the AED after the initial shock. Begin CPR and rewarming until the patient’s core temperature has reached 86º F (30º C). For every degree above 86º F (30º C), the likelihood of successful defibrillation increases.

Evacuation

• Begin a gentle Level 1 Evacuation for all severely hypothermic patients in a solo hypothermia package.

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