Hypothermia

Question 1

What is the pathophysiology of hypothermia?

Answer 1

Hypothermia is a core body temperature below 95°F (35°C). An environmental temperature below 82°F (28°C) can produce impaired thermoregulation and hypothermia in any susceptible person. Therefore people, especially older adults, are actually at risk on a year-round basis in most areas of the world. Wind chill is a significant factor: heat loss increases as wind speed rises. Wet conditions further increase heat loss through evaporation. Weather is a common cause of hypothermia.

Question 2

What are common predisposing conditions?

Answer 2

• Cold-water immersion
• Acute illness (e.g., sepsis)
• Traumatic injury
• Shock states
• Immobilization
• Cold weather (especially for people who are homeless or work outdoors)
• Older age
• Use of medications (e.g., phenothiazines, barbiturates)
• Inappropriate alcohol and substance use
• Undernutrition
• Hypothyroidism
• Inadequate clothing or shelter (e.g., the homeless population)

Question 3

What are mild signs and symptoms?

Answer 3

• Shivering
• Dysarthria (slurred speech)
• Decreased muscle coordination
• Impaired cognition (“mental slowness”)
• Diuresis (caused by shunting of blood to major organs)

Question 4

What are moderate signs and symptoms?

Answer 4

• Muscle weakness
• Increased loss of coordination
• Acute confusion
• Apathy
• Incoherence
• Possible stupor
• Decreased clotting (caused by impaired platelet aggregation and thrombocytopenia)

Question 5

What are severe signs and symptoms?

Answer 5

• Bradycardia
• Severe hypotension
• Decreased respiratory rate
• Cardiac dysrhythmias, including possible ventricular fibrillation or asystole
• Decreased neurologic reflexes to coma
• Decreased pain responsiveness
• Acid-base imbalance

Question 6

What are prehospital care interventions?

Answer 6

• The patient with mild hypothermia needs to be sheltered from the cold environment, have all wet clothing removed, and undergo passive or active external rewarming. Passive methods involve applying warm clothing or blankets. Active methods incorporate use of heating blankets, warm packs, and convective air heaters or warmers. If a heating blanket is used, monitor the patient’s skin at least every 15 to 30 minutes to reduce the risk for burn injury.
• In the case of mild, uncomplicated hypothermia as the only health problem, having the victim drink warm high-carbohydrate liquids that do not contain alcohol or caffeine can aid in rewarming. Alcohol is a peripheral vasodilator; both alcohol and caffeine are diuretics. These effects can potentially worsen dehydration and hypothermia.

Question 7

What interventions are included in hospital care?

Answer 7

General management principles apply to both moderate and severe hypothermia. Protect patients from further heat loss and handle them gently to prevent ventricular fibrillation.

Positioning the patient in the supine position prevents orthostatic changes in blood pressure from cardiovascular instability. Follow standard resuscitation efforts with special attention to maintenance of airway, breathing, and circulation as recommended by the American Heart Association:
- Administer drugs with caution and/or spaced at longer intervals because metabolism is unpredictable in hypothermic conditions.
- Remember that drugs can accumulate without obvious therapeutic effect while the patient is cold but may become active and potentially lead to drug toxicity as effective rewarming is under way.
- Collaborate with the health care provider to consider withholding IV drugs, except vasopressors, until the core temperature is above 86°F (30°C).
- Initiate CPR for patients without spontaneous circulation.
- For a hypothermic patient in ventricular fibrillation or pulseless ventricular tachycardia, one defibrillation attempt is appropriate. Be aware that defibrillation attempts may be ineffective until the core temperature is above 86°F (30°C).

Treatment of moderate hypothermia may involve both active external and core (internal) rewarming methods. Applying external heat with heating blankets can promote core temperature “after-drop” by producing peripheral vasodilation. After-drop is the continued decrease in core body temperature after the victim is removed from the cold environment; it is caused by the return of cold blood from the periphery to the central circulation. Therefore the patient’s trunk should be actively rewarmed before the extremities. Core rewarming methods for moderate hypothermia include administration of warm IV fluids; heated oxygen or inspired gas to prevent further heat loss via the respiratory tract; and heated peritoneal, pleural, gastric, or bladder lavage.

The treatment of choice for severe hypothermia is to use extracorporeal rewarming methods such as cardiopulmonary bypass or hemodialysis. Cardiopulmonary bypass, which requires specialized personnel and resources, is the fastest core rewarming technique. However, this device is not available in all hospitals. Monitor for early signs of complications that can occur after rewarming such as fluid, electrolyte, and metabolic abnormalities; acute respiratory distress syndrome (ARDS); acute renal failure; and pneumonia.

A long-standing principle in the treatment of patients with hypothermic cardiac arrest is that “no one is dead until he or she is warm and dead.” There is a factual basis to this statement when considering the number of survivors who have suffered a prolonged hypothermic cardiac arrest. Prolonged resuscitation efforts may not be reasonable in cases in which survival appears highly unlikely such as in an anoxic event followed by a hypothermic cardiac arrest.