Environmental Emergencies: Hypothermia
Mechanisms that can cause heat loss:
The primary pathways of heat loss include Conduction, Convection, Radiation, and evaporation. While there are intrinsic factors such as hypothyroidism, or hypothalamic dysfunction, that can cause decreased core temperatures, we primarily see hypothermia associated with environmental exposure. Conductive heat loss occurs when the body exchanges heat with a surface it makes contact with. A good example would be a patient lying on ice. Convection occurs when heat is lost through the motion of an object or the environment around it. Wind chill is an example of this phenomena. Radiation is loss of heat to the surrounding environment, as seen in prolonged exposure to cold ambient temperature. Evaporation occurs when heat is lost as a liquid evaporates off of the body.
The human body compensates with several mechanisms. First, shivering is triggered by the hypothalamus, in an attempt to raise core temperature. Next peripheral vasoconstriction is elevated to shunt blood to the core. Metabolism is increased, utilizing glucose in an attempt to generate heat in response to dropping core temperatures. These mechanisms are effective for a short duration, however all are self limiting, particularly if comorbidities such as diabetes, spinal cord injuries, hypothalamic or adrenal dysfunctions, etc are present. Eventually, compensatory mechanisms may fail.
2 common causes of hypothermia are immersion in water, an exposure to cold temperatures while under the influence of alcohol. Immersion in cold water leads to heat loss via conduction, as the heat from the submerged body is lost to the liquid in contact with it. The longer the immersion, the greater the heat loss.
Alcohol is a vasodilator, which means it inhibits the body’s ability to peripherally vasoconstrict in response to cold. This vasodilation also creates a false sense of warmth when alcohol is consumed. Additionally, alcohol limits the ability of the user to sense cold temperatures, and often leads to prolonged periods of exposure to such environments.
Hypothermia:
Hypothermia is technically defines as a core temperature <35 degrees celsius. We grade it as mild-moderate when the core temp is <35 degrees but >32 degrees. It is classified as severe when core temperature drops to <32 degrees. However, hypothermia is more of a spectrum than a black and white condition. Core temperature is difficult to accurately measure in the prehospital environment. We are better suited to assess our patient’s presentation as a gauge for the true severity of their condition. Hypothermia generally presents as follows:
Mild-moderate: -Severe shivering -Cold skin -Mild alterations in LOA
Severe: -Cessation of shivering -Cold rigid movements (if any) -Profound alterations in LOA or Coma
Tympanic or temporal temperatures may be helpful, but are not meant to be the sole metric for determining severity.
Treatment of hypothermic patients:
Mild-moderate: -Move the patient to a warm environment -Remove wet clothing -Cover with warm blankets -Apply warm packs to back of the neck, axillae, and groin
Severe: -Move to warm environment -Remove all wet clothing -Wrap in dry blankets and sheets (consider foil rescue blankets as well) -BE VERY GENTLE. The heart is very prone to ventricular fibrillation in the setting of severe hypothermia. Sudden movements can cause the heart to strike the chest wall and trigger sudden cardiac arrest.Additionally, avoid intubation or other aggressive airway management which may stimulate the vagus nerve, causing the same effect. -DO NOT ACTIVELY REWARM. This must be done in the controlled setting of the ED.
ALL hypothermic patients can benefit from cardiac monitoring, IV cannulation, and BGL testing if possible. These patients can be hypoglycemic and may need intervention.
Additional considerations:
Although we are focusing on the dangers associated with hypothermia, remember that BLS assessment must be completed as taught in order to properly manage your patients and correct all life threats.
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