The chilling effect of hypothermia on trauma patients

Being badly injured is bad enough for trauma patients. However, to be injured and cold presents a much more serious situation from which to recover. As many as 50 percent of trauma patients transported by EMS are unintentionally hypothermic by the time they reach the hospital [1].

Hypothermic trauma patients are less likely to survive their injuries, when compared to similar patients who are normothermic. While there have been studies looking at the use of controlled therapeutic hypothermia for brain and spinal cord injuries, it's still fairly clear at this point that being hypothermic in trauma overall is a significant issue.

As prehospital providers, we can reduce that condition and improve the overall chances of that patient's survival from their injuries.

Causes of hypothermia in trauma patients

There are two basic ways to become hypothermic in trauma. First, the body can quickly lose heat when faced with prolonged exposure to cooler ambient temperatures.

It doesn't have to be "cold" to create a hypothermic environment. EMS involvement can contribute to the problem by infusing large amounts of cool isotonic solutions such as normal saline during volume resuscitation. Large burns will not only weep fluids, but cause a cooling of the body as well.

A second way to lose heat is to not be able to control it well. For example, both the very old and the very young already have impaired thermoregulatory mechanisms.

Certain medications, drugs and alcohol can impair the body's ability to control heat loss. If the injured patient is in shock, the hypoperfusing state can also cause temperature control to fail.

Hypothermia pathophysiology

In trauma, hypothermia begins when the body's core temperature dips below 36 C (96.8 F). Temperatures between 36 and 34 C are considered mild; 34-32 C, moderate; and less than 32 C (89.6 F) is considered severe [2]. 

The effect of hypothermia can cause or contribute to serious conditions such as:

• Poor cardiovascular function, such as ischemia, decreased pumping function, myocardial infarction and cardiac dysrhythmias
• Infection, such as pneumonia and sepsis
• Inability to control internal bleeding due to impaired clotting mechanisms.
• Impaired ability for the liver to detoxify the body of drugs and normally-occurring toxins

Hypothermia in conjunction with metabolic acidosis and impair coagulation creates a "lethal triad," which significantly worsens the chances of recovery from a critical injury. Perhaps even worse, attempting to rewarm a hypothermic trauma may cause even more serious problems as blood that was pooled in the periphery of the body begins to return to its central core, bringing along with it high amounts of waste and acidosis.

Steps to reduce hypothermia

If the patient begins to shiver, it means that hypothermia is beginning to occur. Shivering increases oxygen consumption by the muscle cells by as much as 400 percent.

Therefore, the goal of prehospital care is to avoid the onset of shivering. Basic passive heating measures such as covering the patient and turning on the patient compartment heater until it is uncomfortably warm can slow down the loss rate.

Make sure to remove any wet clothing prior to warming measures. More active warming techniques such as applying heat packs are not warranted in the traumatized patient.

During extended extrications, keep the patient covered with a blanket or sheet. Emergency foil blankets can be very effective in retaining body heat, are light weight and easy to store in a jumpkit.

Infusing large amounts of intravenous crystalloid fluids such as normal saline in a trauma patient not only worsens the ability for the blood to clot, it can also unintentionally cool the body.

Advanced life support providers should use warmed saline and administer only enough fluid to maintain a systolic blood pressure of 85-90 mm Hg [3].

Warming trays are becoming increasingly common on board ambulances as a way to keep IV fluids at the correct infusion temperature. Among the products that can assist EMS providers is the Thermal Angel, which is a great device to warm saline in the field.

Summary

Controlling a patient's body temperature may be as critical as maintaining perfusion pressure in a critically injured patient.

Using simple techniques, EMS providers can significantly affect the outcome of a trauma patient by paying attention to the possibility of nonintentional hypothermia.

References

1. Helm M, Lampl L, Hauke J, Bock KH. Accidental hypothermia in trauma patients. Is it relevant to preclinical emergency treatment? Anaesthesist. 1995 Feb;44(2):101-7.

2.Tsuei BJ, Kearney PA. Hypothermia in the trauma patient. Injury. 2004; 35:7-15.

3. National Association of EMTs. Prehospital Trauma Life Support, 7th Edition. 2010; Elsevier Publishing, St. Louis.