Hypothermia: The Danger of Walking in a Winter Wonderland

If you’re like me, you loved playing in the snow as a kid. If you’re also like me, your mother always scolded you for not wearing enough layers, and she bundled you up in true “I can’t put my arms down!” fashion. She always told me I’d get hypothermia if I didn’t layer up, and I never took her seriously. 

However, my mom had the right idea—hypothermia is a serious condition.

Hypothermia occurs when the body’s temperature goes below 95 degrees Fahrenheit, slowing down your body’s core functions.

Hypothermia and body temperature regulation 

When the temperature outside is cold, the body ramps up heat production to keep itself warm. When the body can’t keep up with the cold and can’t produce enough heat to offset the loss of body warmth from the cold, hypothermia occurs.

Let’s pause for a moment to talk about how the body regulates temperature. The key is the hypothalamus, an area in the center of the brain. The hypothalamus has a plethora of important functions, and one of them is thermoregulation. Using input from the nervous system’s sensory receptors, it keeps track of the body’s internal temperature, and it sends signals out to the rest of the body when that temperature is too low or too high.

The hypothalamus. GIF from VB Suite. 

If the body is too hot, the hypothalamus kicks in like a thermostat, signaling the body to initiate sweating and other thermoregulatory processes. If the body is too cold, the hypothalamus initiates shivering, and the body ramps up its energy use and heat production. 

The systems in the human body function within a relatively narrow temperature range, and when that temperature goes below 95 degrees Fahrenheit, they begin to slow and shut down. For example, the lower temperature disrupts the depolarization of cardiac pacemaker cells, which causes the heart to beat abnormally slowly (bradycardia). 

Signs and symptoms

One of the major dangers with hypothermia is that people might not understand that they are experiencing a drop in body temperature. Because hypothermia slows down the central nervous system, people stop sensing the cold and become confused. 

A person with hypothermia may exhibit:

• Lethargy
• Clumsiness
• Slowed breathing
• Confusion
• Slurred speech
• Irritability 

In the beginning, people with hypothermia shiver intensely, but their shivering reduces as the hypothermia worsens. If they don’t warm up, hypothermia will cause them to fall into a coma, and their breathing and heartbeat will slow to a stop. 

There are three stages of hypothermia. 

Mild hypothermia occurs when the body temperature is between 32 and 35 degrees celsius. The body tries to keep itself warm: the heart and breathing rate increase and the body shivers. When you’re shivering, the movement of your muscles creates more heat. In this stage, the body pushes more blood to the kidneys, which leads to increased urination. 

Moderate hypothermia occurs at 28–32 degrees celsius. Shivering stops, and all body systems begin to slow. 

Severe hypothermia occurs when the body drops below 28 degrees celsius. By this point, the person with hypothermia is typically unconscious. The cardiovascular system continues to slow down, and the loss of circulation causes fluid to build up in the lungs, inhibiting lung function.

Lowering the BPM of the beating heart model in VB Suite. 

Some people with severe hypothermia experience an extremely hot sensation, as their blood vessels open up to push blood into the tissue. Even though they are literally freezing to death, they will take off their clothes in what is called “paradoxical undressing” in response to this unbearably warm feeling.

How is hypothermia treated?

Hypothermia requires professional help—it’s important to call for medical help if you suspect someone has hypothermia. 

While waiting for help, you can remove any wet clothing, make sure the person stays awake, and give the person a dry blanket and a warm drink. 

Well-meaning non-professionals can cause serious damage when they try to rewarm a person with hypothermia. You might think that giving the person a warm bath, putting the person under a heat lamp, or rubbing the person’s cold arms and legs could help—but all these things can put undue stress on the heart and lungs. Additionally, drinking alcohol might give you an internal feeling of warmth, but it actually slows down the rewarming process. 

Once the person with hypothermia is in the care of a medical professional, treatment depends on the hypothermia’s severity.

Shivering indicates that the person’s thermoregulation is still functioning—if a person has mild hypothermia and is still shivering, the person usually receives passive rewarming, being wrapped in warm blankets and given warm fluids to drink. 

If a patient has an internal temperature lower than 32 degrees celsius, has an unstable cardiovascular system, or is experiencing other major problems (like trauma or toxins), active rewarming is needed. 

Active rewarming is when heat is applied to the body. It’s important to apply this heat to the thorax—heat applied to the extremities can overload an already-struggling cardiovascular system. People with moderate hypothermia may be treated with heat packs, and severe hypothermia may call for the use of warmed saline or heated oxygen to reheat the body. 

Part of the cardiovascular system in VB Suite. 

Risk and prognosis

Hypothermia is most common in cold weather, particularly when a person is submerged in water or gets wet. However, hypothermia can occur in temperatures over 40 degrees fahrenheit (about 4.5 degrees celsius) if the person gets wet. Water conducts heat from the body 25 times as fast as air, amplifying the heat loss from cold weather.

Young children and older adults are particularly at high risk for hypothermia. About 50% of the people who die of hypothermia in the United States are over the age of 65. 

Why young children and older adults? Older adults tend to have decreased sensation to temperature, and they are more likely to have mobility and communication problems that keep them from moving themselves somewhere warmer. In addition to the latter, young children lose heat more quickly because of their small size; children have fewer cells to create the heat they need.

Photo from Shutterstock. 

Most hypothermia cases in the United States are in urban areas. They are often a result of environmental exposure, attributed to homelessness, drug and alcohol use, and mental illness. The second largest group of people affected by hypothermia are people who either work or enjoy activities outside, like hunters and swimmers. 

Many people recover from hypothermia well, though mortality rates are higher for those with preexisting conditions or comorbidities. As a MedScape Emergency Medicine article states, “Recovery is usually complete for previously healthy individuals with mild or moderate hypothermia (mortality rate < 5%). The mortality rate for patients with severe hypothermia, especially with preexisting illness, may be higher than 50%.”

Learn more

If you enjoyed learning about hypothermia, check out these other great VB Blog posts!

• A Heated Discussion: Heat Exhaustion, Heat Stroke, and Other Heat-Related Illnesses
• Debunking 5 Holiday Health Myths
• Visible Booze: How Alcohol Affects the Body

Sources

• Visible Body Suite
• Merck Manual, “Hypothermia”
• National Health Service, “Hypothermia”
• Mayo Clinic. “Hypothermia: First aid”
• NIH News in Health. “Halting Hypothermia”
• Centers for Disease Control, “Preventing Hypothermia”
• Openstax, “Energy and Heat Balance”
• MedScape, “Hypothermia”
• The Conversation, “What happens to your body when you get left in the cold”

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