In the Field
Hypothermia in trauma is not what most people picture. It is not someone freezing in the snow. It is a gunshot victim on a 65-degree pavement in July whose core temperature is dropping because they have lost three units of blood. Trauma patients lose heat fast and cannot regenerate it. Every minute spent on cold ground or in a cool room without active warming makes the bleeding harder to stop and the patient harder to save. The "H" in MARCH is there for a reason.
Common Mistake
Assuming hypothermia is only a concern in cold weather environments rather than recognizing it as a trauma-specific physiologic threat at any ambient temperature.
Technical Detail
Hypothermia in trauma medicine is defined more aggressively than in general medicine. While clinical hypothermia in a healthy person typically begins below 35 degrees Celsius (95 degrees Fahrenheit), trauma-induced coagulopathy begins to develop at temperatures as warm as 36 degrees Celsius (96.8 degrees Fahrenheit), which most patients would not even feel as cold.
Why trauma patients lose heat faster. Several mechanisms compound to drive heat loss in trauma patients:
Blood loss removes heat directly. Each milliliter of blood lost carries thermal energy out of the body.
Tissue hypoperfusion reduces metabolic heat production. Cells throughout the body produce heat as a byproduct of normal function. When perfusion drops, so does heat production.
Exposure during treatment increases convective and evaporative losses. Patients are typically exposed for assessment, often on cold ground or vehicle decks, and may be wet from blood, fluids, or environment.
IV fluid administration can introduce cold fluid into circulation. A liter of room-temperature crystalloid lowers a 70 kg patient's core temperature by approximately 0.25 degrees Celsius.
Medications and shock impair shivering and thermoregulation. The body's normal heat-generation responses fail in shock states.
Why hypothermia matters in trauma. Hypothermia is one of the three components of the Lethal Triad. Even modest temperature drops measurably impair coagulation by reducing the function of clotting factor enzymes and platelets. A patient who is bleeding and cold will continue bleeding longer than the same patient warmed to normal temperature. Studies in trauma populations show significantly higher mortality in patients who arrive at the hospital hypothermic, independent of injury severity.
Prevention in the field. Hypothermia prevention is an active, deliberate intervention, not a passive one. Effective field measures include:
Removing the patient from cold surfaces (ground, concrete, vehicle metal).
Cutting away wet clothing and replacing with dry insulation.
Wrapping the patient in a thermal blanket. Commercial products such as the Hypothermia Prevention and Management Kit (HPMK) are CoTCCC-approved.
Limiting exposure during assessment. Expose only what must be examined.
Warming IV fluids when possible. Field fluid warmers are increasingly available in advanced aid bags.
Insulating the head, hands, and feet, which lose heat disproportionately.
Hypothermia prevention is included as the H in the MARCH algorithm specifically because it is easy to overlook in a chaotic scene but contributes directly to mortality outcomes.
