Normal human body temperature is between 36.1 and 37.2° C, while hypothermia is defined as having a core body temperature of less than 35°.1,2 Hypothermia occurs when heat loss exceeds the body’s heat production. One might intuit that hypothermia is solely a result of prolonged exposure to freezing temperatures; however, in the trauma patient, hypothermia may occur as the result of traumatic brain injury, alcohol and drug intoxication, and hemorrhagic shock. Hypothermia also may result from treatment-related causes, including infusion of cold fluids and blood products (stored at 4° C), the use of anesthesia, and from environmental exposure in the emergency department (ED) or operating room.
These conditions impair the body’s autoregulatory ability to maintain normothermic core temperatures.
Patients at the extremes of age are at greater risk of developing hypothermia. The pediatric population is subject to large heat losses due to a higher body surface area to mass ratio, whereas the elderly have an attenuated metabolic response to hypothermia.
High morbidity and mortality rates
Hypothermia is a life-threatening complication of injury and is associated with increased morbidity and mortality in trauma patients with a concomitant decrease in survival. Non-injured patients with primary hypothermia from cold exposure and a core temperature of less than 32° C have a 21 percent mortality rate. The same core temperature in bleeding combat casualties results in 100 percent mortality and is independent of shock, injury severity score (ISS), or fluid resuscitation.3 While ongoing studies are being conducted to investigate controlled hypothermia in traumatic brain and spinal cord injuries, hypothermia remains a common and significant problem in trauma.
A standardized classification system in grading hypothermia in the trauma patient has been devised, with 34–36° C defined as mild, 32–34° C defined as moderate, and less than 32° C defined as severe.4
The lethal triad of hypothermia, acidosis, and coagulopathy is a significant cause of mortality in patients with traumatic injuries. At the cellular level, hypothermia reduces metabolic rate and enzymatic activity—in particular, enzymes of the coagulation cascade. If left untreated, this confluence of conditions often leads to increased blood loss in susceptible patients, worsening acidosis and continued hypothermia.
To examine the occurrence of patients with hypothermia in the National Trauma Data Bank® (NTDB®) research dataset for admissions year 2014, medical records were searched by ED temperature. Records that contained an ED arrival temperature were then divided into two groups: hypothermic, with a temperature less than 35° C (47,845); and normothermic, with a temperature greater than or equal to 35° C (768,774). Of the combined total of 816,619 records, 676,057 contained a discharge status. In comparing the hypothermic group with the normothermic group, 12,547 and 453,135 patients were discharged to home; 10,273 and 70,359 to acute care/rehab; and 4,887 and 97,903 to skilled nursing facilities, respectively. Almost one-third (11,457) of the hypothermic patients died versus 15,496 of the normothermic patients (see Figures 1 and 2).
Figure 1. Hospital discharge status, hypothermic patients
Figure 2. Hospital discharge status, normothermic patients
Among the hypothermic patients, 69 percent were male and an average of 45 years old. The hypothermic group had an average hospital length of stay of 11.5 days versus 4.8 days for the normothermic group; an intensive care unit length of stay twice that of normothermia (10.1 versus 4.8 days, respectively); an average ISS of almost triple (26.6 versus 9.4); and were on the ventilator for an average of 7.4 versus 5.9 days, respectively (see Figure 3).
Figure 3. Average number of days
A significant complication
Hypothermia often complicates the management of major trauma patients and has been shown to increase morbidity and mortality in this population. Advances in care, use of damage control principles when indicated, active warming of resuscitation fluids, and prevention of further heat loss are key factors in managing the lethal triad of hypothermia, acidosis, and coagulopathy. Early recognition and appropriate management should improve survival rates and reduce complications and associated costs. After all, hypothermia results in cold blood and, if left uncorrected, can be a killer.
Throughout the year, we will be highlighting these data through brief reports that will be found monthly in the Bulletin. The NTDB Annual Report 2015 is available on the ACS website. In addition, information is available on the website about how to obtain NTDB data for more detailed study. To submit your trauma center’s data, contact Melanie L. Neal, Manager, NTDB, at email@example.com.
Statistical support for this article was provided by Chrystal Caden-Price, Data Analyst, NTDB.
- U.S. National Library of Medicine. MedlinePlus. Body temperature norms. January 31, 2015. Available at: www.nlm.nih.gov/medlineplus/ency/article/001982.htm. Accessed February 24, 2016.
- U.S. National Library of Medicine MedlinePlus. Hypothermia. January 13, 2014. Available at: www.nlm.nih.gov/medlineplus/ency/article/000038.htm. Accessed February 24, 2016.
- Wang HS, Han JS. Research progress on combat trauma treatment in cold regions. Mil Med Res. 2014;1:8.
- Peng RY, Bongard FS. Hypothermia in trauma patients. J Am Coll Surg. 1999;188(6):685-696.