Hypothermia in the trauma patient: a risk even when it is warm

A casualty is lying on the ground. The bleeding is under control, but their clothes are damp and part of their body has been left uncovered after the assessment. Around them, responders move about, work and barely feel the cold. The casualty has been still for several minutes and still has to wait for evacuation.

This scene does not need snow or freezing temperatures to become a problem. In the trauma patient, heat loss can begin even when the environment feels pleasant to those providing care.

Protecting body temperature is part of casualty care from the first minutes. To understand why, we need to look at both what happens outside the body and what is going on inside it.

Why a casualty loses heat even in good weather

The body produces heat through metabolism and muscle activity. A person who is standing and working can make up for some of the heat they lose. A motionless casualty is less able to do so, and if they are in shock their tissues receive less blood and the situation becomes more complicated.

Added to this are common circumstances in trauma care: clothing cut away to look for injuries, moisture, contact with the ground and exposure to the air. A long evacuation prolongs that loss, even if at first nobody perceives the environment as cold.

That is why we should not wait for the patient to say they are cold or start shivering. Prevention begins as soon as safety and life-saving priorities allow it to be built into care.

Ground, air and moisture: the four routes of heat loss

Heat can leave the body in several ways at once. Through conduction it passes to a colder surface the casualty is in contact with, such as the ground or an uninsulated stretcher. Through convection, moving air carries some of that heat away: this happens with wind, drafts in an open vehicle or a helicopter’s rotor wash.

Evaporation also cools. Wet clothing, sweat or moisture on the skin increase this loss. Through radiation, the body also gives off heat to its surroundings from the areas that remain uncovered.

The image shows why covering from above does not solve the whole problem. Protection must also include what lies beneath the casualty. A foil blanket reduces some losses, but on its own it provides little insulation from the ground.

How temperature relates to bleeding

In a seriously injured casualty, getting cold has consequences that go beyond discomfort. Loss of body temperature impairs the clotting mechanisms and can encourage bleeding to continue.

Hemorrhage reduces circulating volume and worsens tissue perfusion. That lack of perfusion promotes acidosis, which also impairs clotting. If the patient keeps bleeding and losing heat, the three disturbances feed each other.

This cycle is known as the lethal triad: hypothermia, coagulopathy and acidosis. Its practical importance is clear: preventing cooling must go hand in hand with hemorrhage control and the rest of care, as soon as the situation allows.

How to build thermal protection into care

The first step is to separate the casualty from the surface they are lying on. A mat, a pad or a padded stretcher can provide insulation. If the ideal equipment is not available, we will have to adapt the resources at hand and avoid unnecessary movement.

Next, assess moisture. In a sheltered place, if possible, remove wet clothing, dry the skin and replace it with dry clothing. During the examination, uncover only what is necessary and cover each area again once it has been assessed and treated.

If undressing the casualty would expose them even more to wind or rain, the solution must be adapted to the scene. A vapor barrier over the wet clothing, combined with insulation and an outer layer, helps limit losses until a sheltered place is reached.

The wrap should be closed, with no gaps for air to get in. The head is also covered with a hat or a hood, keeping the face clear so breathing and the airway can be observed.

The illustrated sequence combines insulation, active warming and an outer protective layer. When an active warming device is used, follow its instructions and your training: do not place it directly on the skin or underneath the casualty, and watch for the risk of burns.

Protection does not end once the blanket is closed. During the wait and the transfer, check that the layers are still in place, that they have not got wet and that the face remains accessible. Every movement or new assessment can open the wrap and cause the patient to lose heat again.

The mistakes that most easily go unnoticed

One of the most common is judging the risk by how warm the responder feels. The responder is active and may be wearing more clothing; the patient is motionless, exposed and perhaps in shock. They are not in the same situation.

It is also easy to cover the body well and forget the ground, leave the casualty uncovered while equipment is being prepared, or assume that a foil blanket provides heat by itself. The blanket helps retain heat; an active heat source serves a different purpose and requires its own precautions.

Another mistake is leaving prevention until the end. The H in MARCH covers hypothermia and head injury, but the order of the acronym does not mean waiting until the whole assessment is complete before starting to protect body temperature.

Keeping warm throughout the evacuation

Let us go back to the casualty at the start. Controlling the bleeding has resolved an immediate priority, but there is still care to sustain. Insulating them from the ground, limiting exposure, protecting them from moisture and keeping the wrap in place during transfer are all part of that continuity.

Every time the team reassesses the casualty, moves them or hands them over to another resource, thermal protection must remain in place. It is easier to keep body heat than to recover heat that has already been lost.

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