Pre-Hospital Management of Hypothermia

Hypothermia is defined as a core body temperature below 35°C. It may sound like a condition reserved for mountaineers or explorers stranded in Antarctica, but in the wrong circumstances, even the British climate can be life-threatening. Consider a student in Aberdeen who passes out drunk in a garden after a night out, or an elderly neighbour left without heating during a winter cold snap. When the body loses heat faster than it can produce it, core temperature begins to fall, triggering a cascade of physiological changes that can rapidly become fatal if left untreated. Understanding how hypothermia develops, how the body responds, and how to recognise its signs is essential for anyone working in pre-hospital medicine.

Physiology of Thermoregulation

Body temperature is regulated by the hypothalamus, which receives signals through central and peripheral thermoreceptors. When the body loses heat, the hypothalamus attempts to generate heat and reduce heat loss through several mechanisms:

1. Peripheral vasoconstriction

Blood vessels in the periphery constrict to reduce blood flow to these areas, thereby preventing heat loss and redirecting blood to vital organs.

2. Shivering

Shivering is the rapid, involuntary contraction of skeletal muscles, designed to generate heat through increased metabolic activity.

3. Piloerection

The sympathetic nervous system activates arrector pili muscles attached to hair follicles in the skin. Contraction of these muscles results in “goosebumps”, trapping air to act as insulation.

4. Secretion of hormones and catecholamines

Thyroid hormones are secreted to increase the basal metabolic rate, and catecholamines such as adrenaline increase the heart rate and blood pressure, improving the delivery of warm blood to tissues.

The body’s compensatory mechanisms for a low body temperature cannot last long. Without quick correction, these mechanisms fail, and the patient can quickly become critically unwell. Untreated hypothermia can lead to multiple organ failure and can be fatal.

Classification

Hypothermia can be classified as follows:

It is worth noting that most standard thermometers only measure down to 34°C, so low-reading thermometers would be required to accurately stage the severity of hypothermia.

Causes of Hypothermia

The causes of hypothermia can be broadly divided into increased heat loss, reduced heat production, and impaired thermoregulation. The most common reason for increased heat loss is environmental exposure to the cold. Exposure to wind and rain can accelerate heat loss. Some conditions that limit the body’s ability to generate heat include malnutrition, frailty, hypoglycaemia, hypothyroidism, and hypoadrenalism. Normal thermoregulatory mechanisms can be impacted by drug intoxication, stroke, dementia, and head injuries. Alcohol, in particular, is a common contributing factor, as it causes peripheral vasodilation, causing a false sense of warmth. Finally, hypothermia may develop secondary to sepsis, burns or major trauma.

Clinical Features & Assessment

Symptoms of hypothermia may include fatigue, nausea, vomiting, and confusion. The patient may present with cold and pale skin, slurred speech, or altered conscious level, such as agitation or reduced consciousness. Infants may present with a lack of response to stimuli or refusal to feed. It is worth noting that newborn babies lack the shivering mechanism and so are more vulnerable to the cold.

As for all pre-hospital scenarios, ensuring the area is safe and calling for help are the priorities. If the patient is unconscious, check for signs of life. In severe hypothermia, pulse and respiratory rate can be extremely low, so checks should be prolonged for up to 60 seconds if necessary. In cardiac arrest, CPR should be initiated.

In the absence of cardiac arrest, continue to assess as per usual in the ABCDE approach:

There are characteristic 12-lead ECG findings in hypothermia. Most commonly, it will show bradyarrhythmias, including marked bradycardia, atrial fibrillation with slow ventricular response, slow junctional rhythms, or AV block. The Osborne or J wave is a positive deflection at the J point (or negative in aVR and V1). It is usually most prominent in the precordial leads, and the height corresponds with the severity of hypothermia. QT prolongation and cardiac arrest can occur.

Frostbite is caused by ice crystals forming within tissues, usually the extremities. Signs include erythema, oedema, waxy appearance of skin, cyanosis, gangrene and reduced sensation.

Management of Hypothermia

The goal of treatment is to safely increase the patient’s core body temperature by preventing further heat loss and gentle rewarming. 

Preventing further heat loss is essential. The patient should be removed from the cold environment where possible, protected from wind and moisture, and insulated from the ground. Wet clothing should be removed when practical and replaced with dry insulation. Patients should be moved carefully, as excessive movement may precipitate ventricular arrhythmias. The patient should be kept horizontal where possible.

External rewarming can be passive or active. Passive rewarming is appropriate for mild hypothermia in patients who remain conscious and are shivering effectively. Measures include providing dry clothing, warm shelter, and blankets. Shivering generates significant endogenous heat and is often sufficient if further heat loss is prevented. Conscious patients may be offered warm, high-calorie food or drinks.

Patients with moderate or severe hypothermia require active rewarming. Heat should be applied to the trunk, particularly the chest, back, and axillae. Suitable methods include chemical heat packs, warming blankets, and other external heat sources. Avoid warming the limbs, as this can promote peripheral vasodilation and “afterdrop”, where cold peripheral blood returns to the core and further lowers core temperature. Warmed intravenous normal saline can prevent further cooling and support intravascular volume.

Other active internal warming methods that can be provided in hospital include arteriovenous rewarming, haemodialysis, warm saline lavage of pleura and peritoneum, cardiopulmonary bypass and extracorporeal membrane oxygenation (ECMO).

Complications of Hypothermia

Complications of hypothermia and subsequent rewarming include:

Key Learning Points

1. Hypothermia is defined as core body temperature below 35°C.
2. Causes of hypothermia include environmental exposure, sepsis, metabolic disorders, alcohol, and CNS disorders.
3. Patients should be assessed using the ABCDE approach.
4. Classical ECG features of hypothermia include bradyarrhythmias and Osborne waves.
5. The goal of treatment is to prevent further heat loss and encourage gentle rewarming.

References & Further Reading

1. Osilla EV, Marsidi JL, Shumway KR, et al. Physiology, Temperature Regulation. [Updated 2023 Jul 30]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2026 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK507838/
2. Kuht J, Farmery AD. Body temperature and its regulation. Anaesth Amp Intensive Care Med [Internet]. 2021 Aug [cited 2026 Jun 13]. Available from: https://doi.org/10.1016/j.mpaic.2021.07.004
3. Burns E, Buttner R, Hypothermia [Updated 2024 Oct 28] Life in The Fast Lane. Available from: https://litfl.com/hypothermia-ecg-library/
4. Basit H, Wallen TJ, Dudley C. Frostbite. [Updated 2023 Jun 26]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2026 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK536914/
5. Haverkamp FJ, Giesbrecht GG, Tan EC. The prehospital management of hypothermia — An up-to-date overview. Injury [Internet]. 2018 Feb [cited 2026 Jun 13];49(2):149-64. Available from: https://doi.org/10.1016/j.injury.2017.11.001
6. Dow J, Giesbrecht GG, Danzl DF, Brugger H, Sagalyn EB, Walpoth B, Auerbach PS, McIntosh SE, Némethy M, McDevitt M, Schoene RB, Rodway GW, Hackett PH, Zafren K, Bennett BL, Grissom CK. Wilderness Medical Society Clinical Practice Guidelines for the Out-of-Hospital Evaluation and Treatment of Accidental Hypothermia: 2019 Update. Wilderness Amp Environ Med [Internet]. 2019 Dec [cited 2026 Jun 13];30(4):S47—S69. Available from: https://doi.org/10.1016/j.wem.2019.10.002

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Written by: Dr Tze Chien Low (FY1)
Edited by: Dr Maria Kent (FY2, MTB Pre-Hospital Medicine Lead)
Reviewed by: Dr Callum Carruthers (GP with a special interest in Emergency Medicine, and responder with BASICS Scotland)