Hypothermia (Extended Exposure to Cold)

Picture of the stages of frostbite

Hypothermia is defined as a core body temperature of less than 95°F (35°C). Hypothermia occurs when the body's temperature regulation is overwhelmed by a cold environment.

The body’s normal core temperature is 36.5-37.5°C (97.5-99.5°F).

Core body temperature refers to the temperature of the body’s internal organs, like the heart, liver, brain, and blood. Core body temperature is most commonly measured by a rectal thermometer. Continuous measurement can also occur in the hospital with a rectal probe, or a thermometer placed in the bladder or esophagus.

A constant balance occurs between the body generating heat to keep warm and the body losing heat to the environment. The body loses heat in a variety of manners, but conduction heat loss, where heat is lost directly to air or water, is the most common cause of accidental hypothermia.

The body regulates its core temperature of 37°C in the cold by the following two methods:

• By generating heat by shivering and increasing levels of adrenalin (epinephrine) or thyroxine in the blood stream, both of which increase the metabolic rate.
• By heat conservation, most often by narrowing the blood vessels to decrease blood flow to the skin preventing heat loss to the outside environment and keep circulating warmer blood to the core organs.

The most common situations for hypothermia are exposure to cold weather (low temperatures), or partial or complete immersion in cold water.

• Not dressing appropriately for cold weather with prolonged time exposure
• Falling into cold water (such as falling from a boat, or falling through ice into a pond, lake, or stream)

Risk factors for developing hypothermia include the following:

• Elderly, due to lack of reserve to generate heat, underlying medical conditions, and medications
• Infants and children who do not have the reserve to generate heat
• People with mental illness
• People with alcohol or drug problems
• People who are socially-isolated
• Some medications including beta blockers and antidepressants

Some medical diseases or conditions may decrease the body's ability to regulate its internal temperature, including patients with the following:

• Diabetes
• Spinal cord injuries
• Burns
• Hypothyroidism
• Parkinson's disease
• Malnutrition

As the body cools, the symptoms of hypothermia become more pronounced and severe. The sequence of symptoms can be graded as mild, moderate, or severe depending upon the core temperature.

Mild hypothermia symptoms: core temperature 32°C to 35°C (90°F to 95°F)

• Shivering
• Fatigue
• Increased respiratory rate
• Increased pulse rate
• Mild confusion, impaired judgment
• Difficulty with speech and coordination
• Cold diuresis: with shunting of blood to the core organs, increase blood flow to the kidneys promotes more urine production

Moderate hypothermia core temperature 28°C to 32°C (82°F to 90°F)

• Organs start to decrease in function including the heart, kidneys, and brain
• Heart rate slows and heart rhythm abnormalities may occur, including atrial fibrillation
• Respiratory rate begins to slow
• Brain function decreases.
• Paradoxical undressing may occur, where the victim sheds their clothes
• As the victim gets colder, shivering stops

Severe hypothermia core temperature below 28°C (82°F)

• Coma
• Dilated pupils, loss of reflexes
• Decreased blood pressure
• Decreased heart rate
• Lethal heart rhythms like ventricular fibrillation and asystole

The body parts furthest from the center of the body are more susceptible to cold injury and frostbite. These include the fingers, toes, ears, and nose. These areas are even more susceptible in patients with peripheral vascular disease who suffer from poor circulation.

The extremities usually cool faster than the body's core

Newborns, infants, and young children are likely to lose body heat faster because they have a larger surface area compared to body weight. Add this to their relative inability to generate heat by shivering, and infants and children are more susceptible to hypothermia.

The temperatures associated with the severity of hypothermia are similar to adults, but the symptoms may be different.

In mild hypothermia, the infant and child can develop intense peripheral vasoconstriction causing them to appear cyanotic or blue. There is shivering, rapid heart rate and breathing. The victim remains awake.

In moderate hypothermia, the shivering stops, there is decreased consciousness with confusion, and slurred speech or weak cry.

In severe hypothermia, there is loss of brain function with coma and reflexes are lost. Heart rhythm changes occur. As well, there is muscle rigidity that can be mistaken as being frozen solid, but that is not the case. Muscle cells fail to relax and give that appearance.

While adults may not survive severe hypothermia, infants and children have a better prognosis, especially when the hypothermia is due to water immersion.

A hypothermia diagnosis is often made by patient history and physical exam, and is confirmed by measuring the core body temperature.

Hypothermia is a medical emergency and diagnosis and treatment often begin simultaneously at the scene. First responders and paramedics will begin resuscitation and warming the victim even as they evaluate the severity of their condition.

Hypothermia can be life threatening. If a victim is not fully awake and functional after a cold exposure, or if they are in a high-risk group, like the young or elderly, it is appropriate to call for help and activate the emergency medical services (call 911).

The first steps in caring for a hypothermic victim is to get them into a warm place, remove wet clothing, and begin warming them. Warm blankets or insulated blankets are helpful. Rubbing the skin is not advised, since it can cause damage to the very cold skin.

For victims with severe cases of hypothermia, treatment must be gentle as their hearts are at risk for developing lethal rhythms like ventricular fibrillation.

It is also important to remember that the victim may also have a medical condition, or an injury associated with their cold exposure and hypothermia.

External rewarming should continue prior to hospital arrival. Active rewarming with warm water bottles or warm chemical packs can be considered. They are placed on the person's armpits, groin, and abdomen. Be sure the warm packs (about 105.8F or 41C) are not too hot to avoid skin burns.

Emergency department personnel have a variety of rewarming methods that may be considered. Once in the hospital, the core body temperature will be continuously monitored as the body is slowly and gently rewarmed and injuries are evaluated.

For the truly severe hypothermic patient, active internal core rewarming is a possibility using machines that help circulate blood and warm it, or if they are not available, instilling warm fluids into the chest or the abdomen to help warm the body.

All the while rewarming occurs, the patient is monitored for any complications, including heart rhythm problems or core temperature after drop. This occurs when the colder blood from the extremities starts to return back into the warmer center of the body.

Prevention is the best home remedy for hypothermia. Avoid situations and conditions that result in hypothermia. When the weather is cold, plan only essential trips, dress appropriately for the weather, and have supplies available should you become stranded.

If you find someone that is suffering from hypothermia, call for help (911), get them into a warm environment, and check for pulse and breathing. Being trained in CPR is the best possibility to offer the victim help.

The prognosis depends upon the severity of the hypothermia and the previous health of the victim.

Infants and children tend to have a better prognosis after severe hypothermia than adults.

If the person with mild hypothermia is treated quickly, does not require hospitalization, and has little or no residual problems, the prognosis is usually very good. Some patients may suffer from frostbite, and there is a potential that they may be more prone to develop hypothermia in the future.

People that have concurrent problems (the elderly, those with alcohol and drug abuse, those with psychiatric conditions and the homeless) have a worse prognosis, and their mortality rate is higher.

Hypothermia is a preventable injury and there are common steps to decrease the risk of succumbing to the cold.

• Rooms should be heated to a minimum of 16°C (61°F) to decrease the risk for hypothermia in infants and the elderly. Keep at least one room in the house nice and warm.
• Stay well hydrated, drink plenty of fluids and warm drinks.
• Avoid alcohol and nicotine.
• Eat regular meals to stay well nourished. Keeping warm in cold weather burns plenty of calories.
• Check with your doctor to see whether any medications might affect your ability to maintain a normal body temperature.

When you go outside:

• dress in layers
• be active, but avoid sweating
• wear a hat, almost 30% of body heat can be lost through the head
• wear a scarf and gloves, and avoid exposing bare skin
• change out of cold and wet clothes as soon as possible