Physician's Perspective

As Temperatures Plunge, Risk of Hypothermia Rises

Steven R. Gambert, MD, AGSF, MACP Editor-in-Chief, Clinical Geriatrics®

As we enter 2013, bitterly cold weather, snow, and ice are abundant in many areas of the country, but it does not take a winter blizzard to cause serious injuries. Recently, I was asked to help care for an elderly woman with dementia who wandered away from her home one evening. Her son recognized her absence only after a few hours had passed and called the police, who sent out a search party. She was eventually found one mile from her home not wearing shoes or protective clothing. Upon entry to the emergency department, her core body temperature was 80.6°F. She had an altered level of consciousness and was quickly intubated to assist with her breathing. She had renal failure and remained lethargic despite rewarming. Presently, she remains on supportive care measures. Given this serious situation, I thought it would be a good time to review the major aspects of hypothermia. 

Hypothermia is a condition in which the core body temperature drops below 95°F. Under normal conditions, body temperature is kept within a tight margin of 97.7°F to 99.5°F. This is achieved through a series of biological factors that result in shivering and nonshivering thermogenesis. As we age, however, our ability to sense change in environmental temperature as well as our ability to respond to this change are both altered, resulting in a diminished ability to maintain an optimal body temperature. While hypothermia is most commonly found when an individual is exposed to extremely low temperatures, elderly persons may become hypothermic even at room temperature. 

Reduced muscle mass with aging can hinder the mechanisms of generating body heat, even if one begins to shiver. In addition, older individuals appear to be less able to recognize changes in environmental temperature and are less able to respond as quickly to maintain thermoneutrality. Therefore, older individuals must be especially careful not to be exposed to extreme environmental temperatures. I have seen many older persons become hypothermic at room temperature when they fell onto a tile or linoleum floor and remained there for a period of time; exposure to a colder surface is an additional risk factor for the loss of body heat. 

As body temperature declines, shivering and mental confusion are often noted, although an older person can become hypothermic without ever shivering. Age-prevalent diseases, such as hypothyroidism, and use of certain medications, such as beta-blockers, may interfere with temperature-generating mechanisms that involve the catecholamines and thyroid hormones  responsible for nonshivering thermogenesis. 

Signs and symptoms of hypothermia vary depending on its degree of impact. In general, mild hypothermia may be accompanied by symptoms associated with sympathetic nervous system excitation, including shivering, hypertension, tachypnea, tachycardia, and vasoconstriction. Increased urination, confusion, and even hepatic and renal dysfunction may be noted. Hyper-
glycemia may also be present as both glucose consumption by cells and insulin secretion may decrease and tissue sensitivity to insulin may be blunted. Sympathetic activation may also cause glucose to be lost from the liver. 

As the body temperature further decreases, shivering may become more significant, and problems with muscle coordination may result. Confusion is common and ambulation becomes increasingly more difficult and dangerous, with individuals often stumbling, increasing their risk of falling. Skin becomes more pale and the ears, lips, and toes may show signs of cyanosis. 

When severe hypothermia occurs, speaking may become difficult and memory may become greatly impaired. Cellular metabolism begins to be impaired as well. Exposed skin commonly becomes blue and puffy. Body temperatures below 86°F are often accompanied by severe ambulatory dysfunction, incoherent/irrational behavior, or even stupor. Pulse and respiratory rates may decrease significantly while tachycardia and/or atrial fibrillation may also occur. As the temperature further plummets, systems begin to shut down. Heart rates as low as the 30s are not uncommon when body temperature reaches 84.2°F. Major organs may fail and death may result. 

Approximately 20% to 50% of persons who die of hypothermia experience a phenomenon called paradoxical undressing. Despite having moderate to severe hypothermia and being exposed to low environmental temperatures, these individuals begin to disrobe, further increasing their rate of heat loss. It has been postulated that there is a cold-induced malfunction of the hypothalamus—the part of the brain that helps regulate body temperature—or that as muscles contract, peripheral blood vessels become exhausted and relax, leading to a sudden surge of blood (and heat) to the extremities, which causes the individual to feel overheated. This finding has also been linked to a behavior known as terminal burrowing, in which individuals seek out small enclosed spaces, such as underneath beds or behind pieces of furniture. 

Core body temperature must be measured using a temperature probe to measure temperatures below 94°F. A low-temperature thermometer can be placed rectally, esophageally, or in the bladder. Electrocardiography findings often show the Osborn J wave, ventricular fibrillation is common when body temperature drops below 82.4°F, and asystole often occurs at core temperatures below 68°F. 

Treatment is supportive in most cases and rewarming can be achieved using either passive external rewarming, active external rewarming, or active internal rewarming. Placing a hot water bottle under both armpits and by the groin is particularly well accepted for moderate hypothermia and easy to do in the field if necessary. Extracorporeal rewarming is the fastest method for persons with severe hypothermia. Since diuresis is common in the setting of hypothermia, dehydration is commonly found upon presentation. For this reason, intravenous fluids are often advised (250 mL-500 mL 5% dextrose and normal saline warmed to a temperature of 104°F-113°F). A side effect of rewarming is the entity known as rewarming vascular collapse or rewarming shock. This entity occurs due to a sudden drop in blood pressure in combination with a low cardiac output, and it is most often seen during active treatment of a severely hypothermic person. 

While early treatment and supportive care are the best ways to treat hypothermia, the best way to prevent it is to avoid cold exposure in the first place. Older persons must be provided with a warm environment and given attention to adequate protective clothing when going outside. Layers of clothing, including hats, scarves, and gloves, often provide the best insulation against the cold by helping to maintain body temperature. Individuals who are at risk of wandering and being outside without supervision or protective clothing should be identified. The use of “warning devices” an older person can use if they fall may also help bring relief prior to a drop in body temperature from laying on a cold surface for a prolonged period of time. As with so many other aspects of medicine, prevention is key!