What is Hypothermia?

Hypothermia is a condition in which the core body temperature (CBT) drops below 35°C (95°F). It can be caused by internal and external stressors and if untreated, hypothermia can lead to serious consequences.

Woman drinking hot drink to prevent hypothermia/keep her core body temperature high - By morozv

morozv | Shutterstock

CBT is a very tightly controlled physiological parameter that is typically held between 36.5°C (97.7°F) and 37.5°C (99.5°F); referred to as the thermoregulatory zone. In order for the body to maintain it’s CBT, there must be a constant balance of heat production and loss.

Heat production occurs through metabolism, as well as through muscle contraction, whereas heat loss may occur via a number of ways. Just over half of the body’s heat is lost via radiation in dry and cold conditions, while conduction and convection account for approximately 15% of further heat loss.

The remainder of the body heat is lost through evaporation and respiration. When immersed in water, heat loss by conduction is significantly increased.

What are the causes of hypothermia?

In hypothermia, the body’s capacity to regulate its CBT is overwhelmed as a result of a cold stressor, which may be intentional or accidental. There are two types of hypothermia, and these are known as primary and secondary. Primary hypothermia is caused by an external environmental stressor alone and the absence of any medical conditions that could cause a disruption in thermoregulation.

Secondary hypothermia occurs when there is internal interference of the hypothalamus-controlled temperature set-point by a medical condition, thereby leading to a drop in body temperature. Examples of such medical conditions include infections, poisoning by toxins, and metabolic, as well as central nervous system disorders.  

Hypothermia may be intentionally induced in a patient as an attempt to confer neuroprotection after experiencing a medical condition that puts them at risk for such (e.g. following a stroke or cardiac arrest).

An unanticipated, accidental exposure to a cold stressor could occur as a result of numerous situations. For instance, an outdoor enthusiast may become incapacitated on a high altitude mountain for a period longer than the protective gear is able to withstand. Another example of an individual at risk for hypothermia is a person without shelter during a cold winter storm.

What are the symptoms of hypothermia?

The symptoms of hypothermia are dependent on the degree of the hypothermia, which can range from mild or moderate to severe. When mild or moderate, hypothermic patients present with symptoms that can be fairly misleading, these include, but are not limited to dizziness, confusion, dyspnea and chills. Moreover, these patients may be irritable and have mood changes, lassitude and poor judgment.

These symptoms are misleading, because they may be mistaken for other medical conditions, such as alcohol intoxication and stroke. In severe cases, patients with hypothermia may present with cardiac arrest and/or coma.

How is hypothermia diagnosed and treated?

The physical signs and symptoms of hypothermia, as well as the conditions in which a person was found, give an apparent diagnosis. However, a readily apparent diagnosis may not be the case in patients with mild hypothermia. This is especially seen in older hypothermic patients, who are indoors and present with symptoms such as confusion, speech difficulties and a lack of coordination.

Therefore, it is important to measure temperature, preferably rectally, with specialized low-reading thermometers in order to avoid any false readings with standard clinical thermometers that may not read below certain temperatures. It is crucial to prevent further heat loss and rewarm the CBT in hypothermic patients without delay.

Additional focus should be placed on treating and/or avoiding any malignant cardiac rhythms. To prevent the latter, in particular, it is important to not cause any inadvertent and unnecessary jerky movements of patients who are severely hypothermic.

In preventing further heat loss, it is imperative to remove the patient from the environment that is conducive to such. For instance, wet clothing should be removed and replaced with dry and warm blankets.

Active external rewarming with heat packs placed strategically in areas such as the abdomen, groin and axillae should be done. If necessary, and in dire circumstances when heat packs are not available, active rewarming may also be achieved with body-to-body contact.

Depending on the degree and severity of the hypothermia, active rewarming of the CBT may be achieved with the infusion of warmed electrolyte solutions, administration of warmed humidified oxygen, lavage of the body cavities with warmed isotonic fluids, and extracorporeal blood warming.

Further Reading

Last Updated: Nov 28, 2018

Damien Jonas Wilson

Written by

Damien Jonas Wilson

Jonas is a medical doctor from St. Martin in the Carribean. He recently graduated with a Medical Degree (MD) from the University of Zagreb Teaching Hospital. His training in general medicine and surgery compliments his degree in biomolecular engineering (BASc.Eng.) from Utrecht, the Netherlands. During this degree, he completed a dissertation in the field of oncology at the Harvard Medical School/ Massachusetts General Hospital

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