Hypothermia: what happens when our body loses the battle with the cold?

On September 14, 2022, climbers discovered the frozen and lifeless bodies of two tourists in the Spanish Pyrenees at an altitude of 2500 m. The victims, an experienced couple in their sixties, were taken to a Barcelona hospital, but they could not be saved.

When she arrived at the emergency room, her core temperature dropped to just 16°C.

This tragic outcome reminds us that hypothermia can surprise even the most cautious and that the cold is literally deadly.

how do we lose heat

Fortunately, we are not completely defenseless against the cold. Our body has methods to stay warm and limit heat loss.

Our ideal body temperature is around 36.6°C. This is the ideal point for cell development. Your proteins are more efficient, as are your mitochondria, your energy factories. All these mechanisms make up the internal metabolism, and our precious heat comes from its work.

But this internal heat can be easily lost in four main ways:

• By radiation, on the surface of the skin (the most important source of losses);

• By conduction, through direct contact with a cold surface (widely used when hot);

• By convection. The air forms an insulating layer around our body, which is destroyed by the wind;

• By sweat. When water evaporates from the surface of the skin, it carries away heat.

When heat loss is greater than heat production, our temperature drops. That’s when our body’s emergency response mechanisms kick in to maintain our temperature (at least for a little while).

Our body’s temperature control center is located in the hypothalamus, a small area located at the base of the brain. It works like an extremely precise thermostat and responds to information received through ultra-sensitive sensors located in the skin, spinal cord, abdomen and veins.

At the slightest deviation from 36.6°C, our internal boiler lights up. Increases heat production and reduces heat loss through involuntary mechanisms:

• Piloerection or goosebumps: Our hairs stand on end to expand the insulating layer of air.

• Chills: Our muscles contract to increase metabolism fivefold and produce more heat.

• The redirection of warm blood away from cold outer surfaces, hence our pale skin.

So even if your fingers and toes are cold when you walk in the snow, your internal organs are still at 36.6°C. Physiologists call this the ability to maintain a constant internal temperature, or “homeostasis,” regardless of external conditions.

And that’s not all: cold also causes behavioral responses. In addition to our body, the hypothalamus also informs the higher parts of the brain about the situation, managing logic and finding solutions. This is what makes us look for warmer places, take shelter from the wind, drink something hot…

Physical effects of hypothermia

But our ability to resist the cold has its limits: too light or wet clothing in frosty weather, too much time outside… When these limits are exceeded, the body begins to cool from the inside. Hypothermia occurs when our core temperature drops below 35°C.

Depending on the symptoms and the measured body temperature, there are four stages of hypothermia (according to the Swiss system). At a body temperature of 28 to 35 ° C, they speak of mild to moderate hypothermia; below 28°C, from deep hypothermia; below 20°C, severe hypothermia.

Two degrees below normal core temperature is enough to reduce the activity of our proteins and cause our cell metabolism to drop to such a low level that it threatens the functioning of vital organs.

If these signs are not addressed in time, the situation can quickly become life-threatening. The physical effects of hypothermia are numerous:

• The heart beats more slowly, resulting in a weak pulse. This reduces blood clotting.

• Our reduced metabolism weakens the lung muscles. Our breathing (inhalation and exhalation) becomes slower, more shallow.

• Chills appear at first, but as our mitochondria become less efficient, the energy supply decreases. After a certain point, we stop shaking, which is an important alarm signal.

Confusion and loss of consciousness

But the best indicators of hypothermia may be changes in behavior: people show confusion, do not realize that they are cold (because it happens gradually), speak more and more slurred and behave strangely.

For example, cases of “paradoxical stripping” have been reported. As the hypothalamus gets knocked down, the victims think they are hot and begin to undress. They are found naked but huddled together in an enclosed space, indicating an animal reflex to retreat to protect themselves.

So, the level of attention worsens, coordination weakens, risky behavior increases. Finally, there is a loss of consciousness, which can lead to death due to cardiac arrest and a prolonged lack of oxygen in the brain.

In a last-ditch effort to stay alive, our internal control mechanisms cut off the warm blood flow to limbs such as arms and legs. Body heat is conserved for vital organs.

Children and the elderly, the most vulnerable

There are a number of factors that contribute to hypothermia and how quickly it can worsen.

Water conducts heat 24 times faster than air. In cold weather, sweating (and therefore strenuous physical activity) should be avoided as it causes significant heat loss.

Age is also an important factor. Children are at greater risk because their skin surface is very large in relation to their body, resulting in rapid heat loss. Their muscles still don’t allow them to shake effectively. Young people have a special type of fat called “brown fat” (rich in mitochondria) that produces extra heat, but not much of it.

In the case of older people, the problem is that their body is less able to perceive changes in temperature. Its internal thermostat is less efficient and no longer responds optimally to cold.

On the other hand, alcohol increases heat loss by dilating the blood vessels in the skin. And its abuse impairs thinking and increases risky behavior. Certain medications and medicines, especially antidepressants, can have similar effects.

Some disorders, such as anorexia or hypothyroidism, can also reduce our resistance to cold.

Do?

Do not hesitate to provide first aid to a person suffering from hypothermia. Every minute counts!

Call a doctor and move the victim to a warmer place, but avoid heating too quickly as this is dangerous. In this case, remove wet clothing. Give him a hot soft drink and cover him with blankets and dry clothes. It is better not to rub the skin or expose it to direct heat, such as a hot water bath (which can cause burns). In the most severe cases with loss of consciousness, transfer to the intensive care unit is necessary.

In 1999, Swedish Anna Bogenholm spent 80 minutes in icy water after a skiing accident. When she was rescued, doctors measured the lowest body temperature ever recorded – 13.7 ° C. To everyone’s surprise, he recovered. Sudden hypothermia sometimes appears to “cryoprotect” tissues, leading to the conclusion that no one can be declared dead until they are warm.

This understanding is currently being applied to better preserve organ transplants and better protect vital organs during long-term heart surgery by injecting cold fluid into the bloodstream.

So during cold snaps, make sure you protect yourself and vulnerable people, young and old. Wear dry, windproof and water-repellent clothing, especially around the face and head. For those who are homeless, lonely, or unable to take care of themselves, social services can be of great help, just like you.

Peter Vankamp, ​​Postdoctoral Fellow, National Museum of Natural History (MNHN)

This article was originally published on The Conversation. Read the original.