You’re working the night shift in the ED when the ambulance radio crackles to life. Prehospital personnel are en route with a 32-year-old man who lost control of his car and careened off the road into a tree. The hands on the clock mark off the precious minutes of trauma’s “golden hour” — the 60 minutes after a trauma during which lifesaving interventions have some of the greatest impact on morbidity and mortality. The decisions that you and the rest of the trauma team make will have a significant effect on this patient’s short- and long-term morbidity and mortality.

As the nurse on the trauma team caring for this patient, one of your responsibilities is to assess and monitor vital signs: blood pressure, pulse, respiratory rate, and oxygen saturation. But what about the other vital sign? What about temperature? Is temperature measurement really that important during this early resuscitative period? Will it change your treatment decisions?

Recent research indicates that temperature, specifically decreased body temperature, or hypothermia, plays a pivotal role in the long-term outcome of the traumatically injured patient and should be one of the routinely measured vital signs.¹ This module will explore the risk factors and effects of hypothermia on the critically injured patient and will examine the nurse’s role in recognizing, preventing, and treating this potentially deadly condition.

Too cold for comfort

When the word hypothermia is mentioned, visions of a child falling into a frozen lake or a climber trapped for hours on a snow-covered rocky precipice may come to mind. These scenarios encompass the traditional view of hypothermia, which is defined as a body temperature below 35 C (95 F) and severe hypothermia as a body temperature below 32.2 C (90 F).² Many predictable changes occur to body systems when the core temperature reaches these levels. It is now recognized that many of these deleterious body system changes also affect trauma patients whose core body temperature is allowed to drop, even if they are not exposed to extreme environmental conditions.

More specifically, traumatically injured patients may be susceptible to these negative effects at much higher temperatures. In the face of trauma, mild hypothermia is defined as 34 C to 35 C (93.2 F to 95 F), moderate hypothermia as 32 C to 34 C (89.6 F to 93.2 F), and severe hypothermia as less than 32 C (89.6 F). At 34 C, a crucial core temperature, significant increases in mortality occur.³ Body temperatures at or below 32 C (89.6 F) are associated with 100% mortality.⁴ Overall, studies have found a threefold increase in mortality in hypothermic trauma patients when compared to normothermic trauma patients, even when factors such as varying age, injury severity, admission systolic pressures, and temperature measurement routes were adjusted for.³ As such, nurses need to be aware of the important role they play in monitoring and preventing hypothermia in this population of patients.

Who’s at risk

With the knowledge that hypothermia increases the mortality rates of trauma patients, it is distressing to learn that an estimated 50% to 66% of trauma patients arrive in the ED with core temperatures below normal.^1,5 And as many as 57% of traumatically injured patients will leave the ED in a hypothermic state.⁶ Numerous risk factors contribute to the high percentages of hypothermia in this patient population, including:

Shock states: A majority of traumatically injured patients develop shock, which results in vasoconstriction to nonessential organs and the periphery. Vasoconstriction decreases cellular metabolism to the nonperfused cells throughout the body. Cellular metabolism is one of the body’s main heat-producing mechanisms, contributing to hypothermia. Therefore, decreased metabolism increases risk for hypothermia

Fluid resuscitation: Most ambulances do not have the ability to warm IV fluids, so they are most often administered at or below room temperature, which is generally 13.5 C to 16.5 C (25 F to 30 F) below body temperature. Each liter of fluid infused at room temperature has the potential to lower body temperature by 0.5 C (0.9 F).⁷ Some EDs also infuse IV fluids at room temperature, further exacerbating the problem.

Area of injury: Injuries to the extremities, the pelvis, the abdomen, and large blood vessels are more likely to result in hypothermia.¹ This is in direct comparison with areas such as the head and chest, which have a lower incidence of hypothermia following injury.

Environmental factors: Exposure of patients to the ambient environmental temperature as the result of removing their clothing for assessment and stabilization increases hypothermia risk. Also, exposure of the patient’s body to blood-soaked or damp clothing and dressings further contributes to hypothermia.

Alcohol use: Patients who have been using alcohol may have impaired heat regulation, further increasing their risk for hypothermia.⁷

Infusion of blood products: Infusion of refrigerated blood products can lower body temperature by 0.25 C (0.5 F) per unit of blood.⁷

Use of anesthetics and paralyzing agents for intubation and surgical procedures: These agents can decrease vasoconstriction as well as shivering thresholds, potentially decreasing heat production by one-third.¹

Exposure of body cavities during surgery: Despite rewarming techniques in the surgical suite, evaporative heat loss may be as high as 4.6 C (8.2 F) per hour.⁸

Far-ranging effects

Hypothermia has profound effects on numerous body systems, which can alter the long-term outcomes for the patient. The anticipated negative effects of hypothermia on the different body systems include —

Cardiovascular system: A trauma-induced increase in sympathetic activity results in vasoconstriction and tachycardia. Vasoconstriction contributes to tissue hypoxia and increases lactic acid production, thus exacerbating acidosis. Acidosis increases the risk for coagulopathies, resulting in prolonged bleeding, hypovolemia, and disseminated intravascular coagulation (DIC). Tachycardia increases myocardial oxygen demands, which if extreme, may result in hypoxic-related atrial and ventricular arrhythmias.⁵ Additionally, as the temperature falls below 32 C (89.6 F), heart rate and cardiac output decrease, worsening tissue oxygen delivery and contributing to acidosis and the potential for arrhythmias.¹

Pulmonary system: In early hypothermia, the respiratory rate may increase. However, as the temperature drops, the rate will decrease, negatively affecting oxygen delivery. Hypothermia also shifts the oxyhemoglobin dissociation curve — the relationship between available oxygen and amount of oxygen carried by hemoglobin — to the left, resulting in decreased oxygen delivery to the tissues, further worsening lactic acidosis.⁵ After the acute resuscitation period and during the rewarming process, patients may experience excessive production of bronchial secretions and a depressed cough reflex. These symptoms may contribute to complicated pulmonary sequelae, such as respiratory infections and pulmonary edema in the rehabilitative period.¹

Central nervous system: Cerebral blood flow decreases 6% to 7% for every 1 C (1.8 F) decline in core temperature, decreasing oxygen delivery to the brain.⁹ This can exacerbate existing brain injuries and result in changes in patient sensorium.

Renal system: Hypothermia may suppress reabsorption of sodium and water in the distal renal tubules. This leads to diuresis, despite decreased glomerular filtration rates, and is sometimes referred to as “cold diuresis.”¹ Cold diuresis increases fluid losses, further compounding hypovolemia.

Acid-base balance: As mentioned earlier, hypothermia increases acidosis risk via several mechanisms. More specifically, decreased tissue perfusion secondary to cardiovascular suppression, coupled with shivering, contributes to lactic acid production. The accumulation of lactic acid results in a state of metabolic acidosis. Because hypothermia suppresses the normal hepatic function of lactate clearance, the acidosis worsens.¹ Acidosis, in turn, primes the patient for increased bleeding tendencies and coagulopathies such as DIC.

Endocrine system: Elevated catecholamine levels intensify glycogenolysis, the breakdown of glycogen stores to produce glucose, which increases circulating blood glucose levels. Hyperglycemia suppresses the phagocytic abilities of certain white blood cells, thereby predisposing the patient to infection and sepsis.

Coagulation effects: The effects of hypothermia on the trauma patient increase bleeding risk. More specifically, enzymatic reactions for blood clotting are temperature dependent and when altered, result in excessive bleeding. Also, hypothermia stimulates fibrinolysis and decreases platelet function. These many alterations delay the natural coagulation of bleeding associated with trauma, as well as prime the patient for a deadly complication of trauma: DIC.

Knowledge of the negative effects of hypothermia and the consequences of these effects on patient mortality should motivate the trauma team to carefully monitor for decreased body temperatures. Measurement of temperature must be included on the list of integral vital signs, which are closely monitored in early resuscitation.

Hospitals with continuous temperature monitoring capabilities should employ this technology early in the resuscitative process. Examples include Foley catheters with continuous core temperature measurement devices or rectal sensors that provide continuous temperature measurement. In the absence of such technology, the trauma unit may choose to monitor temperature through the most appropriate intermittent device: oral, rectal, tympanic, surface, or axillary thermometers. Facilities should consider policies that institute rapid measurement of body temperature after the patient arrives and continuous or frequent temperature checks during initial resuscitation and in the surgical suite and intensive care unit.

Warming up

Nurses can employ a number of strategies to prevent hypothermia in trauma patients and to elevate the temperature of those who show signs of decreased temperature. The most obvious intervention is to increase the ambient temperature where patient care will take place. The thermoneutral zone of humans is 25 C to 30 C (77 F to 86 F), which is the temperature at which humans are able to maintain their temperature without creating or releasing body heat.¹ While it is unrealistic to maintain trauma resuscitation rooms and patient rooms at this elevated temperature, the closer healthcare practitioners can come to maintaining a warm environment, the more they can protect the patient from heat loss.

Interventions used to protect the trauma patient from heat loss include keeping the doors to the trauma room and patient rooms closed to prevent drafts from further cooling a patient and replacing all wet clothing, dressings, and bedding with dry counterparts to prevent evaporative heat losses. Moreover, the simple act of keeping a patient covered can significantly reduce the incidence of trauma-related hypothermia. While this intervention may seem obvious, it can be difficult during a hectic resuscitation. Trauma care involves assessment of the entire body, which necessitates removal of all clothing. It is also not uncommon for multiple trauma team members to be performing interventions on various parts of the body simultaneously, requiring exposure of a large surface area. Covering the trauma patient with blankets, exposing only small areas required for assessments and interventions, can maintain existing body heat and should be a goal of all trauma team members.

Special blankets such as fluid-circulating, convective-air, and aluminum space placed over and under the patient may create a 43 C (109.4 F) environment around a patient. This can be augmented by placing standard cotton blankets on top of the patient and securing the edges under the side of the bed.¹⁰ While this technique is excellent in maintaining and elevating body temperature, it severely limits access to the patient and is often reserved for use after the patient has been stabilized. Overhead radiant warmers may also be used but with caution to prevent burns to the skin.

One often overlooked method is the use of head coverings. As much as 50% of radiant heat loss occurs from the level of the neck and above.¹⁰ Covering the patient’s head with towels, shower caps, or a commercially prepared aluminized cap may assist in preventing further heat loss.

As stated earlier, the use of room temperature intravenous fluids may be a major source of hypothermia risk during early trauma resuscitation. Always consider using prewarmed intravenous fluids. Different techniques can successfully facilitate this process, including prewarming fluids in a commercially prepared warmer or using rapid infusers, which simultaneously warm solutions to a preset temperature. Similarly, all blood products administered should be warmed to body temperature using similar techniques with careful oversight by the blood bank to assure the procedures maintain the integrity and safety of blood products.

In the patient who is already exhibiting indications of hypothermia, a variety of techniques may be considered to assist in body temperature elevation. If the patient is receiving oxygen, consider delivering the oxygen through saline or sterile water that has been prewarmed. If, on the other hand, the patient is intubated and mechanically ventilated, humidified ventilator circuits can be warmed to 41 C (105.8 F).¹⁰

Heating body cavities may also be considered, although these techniques are time-intensive and may not yield significant elevations in temperature. These techniques involve introduction of a heated lavage solution into the gastric tube, urinary catheter, peritoneal catheter (into the abdominal cavity), or as an enema into the lower bowel. At times, heated lavage solution may also be introduced into the pleural cavity via chest tubes.

One technique used in some trauma centers is known as continuous arteriovenous rewarming (CAVR). Femoral catheters are placed arterially and blood is removed from the body under the patient’s own systolic pressure. The blood is circulated through a fluid warmer and returned to the body via a venous femoral catheter. This technique can quickly and safely elevate core temperatures; however, its use is limited because of the lack of equipment in many facilities and the learning curve associated with safe implementation.

Hypothermia in the traumatically injured patient is not limited to the initial resuscitation room. The deleterious effects extend into the surgical suite and ICU, as well. The techniques described here should be considered throughout the continuum of care in the initial hours and days after trauma has occurred. Additional considerations for the surgical suite include abbreviated surgical interventions such as direct control laparotomy (DCL), which involves only a brief surgical procedure to control bleeding and implement lifesaving repairs. After such repairs are made, the patient is then transferred to the ICU where temperature control can be maintained. More definitive surgical repairs will be considered after the patient’s condition and temperature have been adequately stabilized. Overall, DCL helps to reduce the heat loss associated with surgical interventions.

Let’s return to questions posed in the beginning of this module. Is temperature measurement in the trauma room important? Will it change our treatment decisions? It should be obvious at this point that, yes, temperature measurement is integral to holistic trauma care and may have long-term consequences to patient outcome. With hypothermia exerting potential negative effects to a majority of the body systems, thus priming the patient for such sequelae as septicemia, DIC, metabolic acidosis, and cerebral hypoperfusion, members of the trauma team need to pay careful attention to patient temperature throughout the early resuscitative period, including in the trauma room, operating room, and ICU. Efforts must be made to quickly reverse hypothermia, which may exist before hospitalization, and interventions should be instituted to prevent further heat loss once the patient is hospitalized.