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Hypothermia in Trauma
Running head: HYPOTHERMIA IN TRAUMA PATIENTS
Hypothermia in Trauma Patients: Incidence, Pathology, Prevention & Treatment
Frederick D. Watters
University of Pennsylvania
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Hypothermia in Trauma
Abstract
The purpose of the review is to examine the challenges of critically injured patients with
co-existing or secondary hypothermia and the research published in the past decade addressing
these issues. Using the search terms ‘trauma’ and ‘hypothermia,’ computerized searches of the
MEDLINE, CINAHL, and Pre-MEDLINE databases were conducted. The primary research
concerning hypothermia in trauma patients was organized into three general categories for the
purpose of analysis: 1) Incidence, 2) Pathology, 3) Prevention and Treatment. The body of
evidence is lacking in three main areas: 1) sample size, location, and continuity of care; 2)
variability of injury severity and measurement; and 3) temperature measurement variations.
Future research should focused on hypothermia during trauma resuscitation and nurses’ roles in
initial recognition and treatment. The nursing literature must be updated to reflect the clinical
research understanding of pathology and recommendations for practice.
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Hypothermia in Trauma Patients: Incidence, Pathology, Prevention & Treatment
In the late 1980’s and early 1990’s, the US healthcare system saw an unprecedented
surge in severe trauma, primarily related to the incidence of penetrating injuries reaching
epidemic proportions. The creation of a nationwide trauma system ushered in the concept of
“the golden hour,” the critical timeframe for transport to definitive hospital care. This short
window of opportunity has driven the evolution of advances in trauma resuscitation. Patients
who would have died at the scene in years past are now arriving in the emergency room alive.
Patients who would have died in the emergency room are surviving into the operating room.
These advances in care have been accompanied by new problems that need to be addressed. One
of these clinical challenges is hypothermia
The late 1980’s saw a surge of research investigating the incidence of hypothermia in
these trauma patients. Anecdotal evidence grew into an understanding of an insidious cycle of
hypothermia, acidosis, and coagulopathy that was killing many patients despite their quick
transport and care in the hands of highly trained medical professionals. By 1991, research
studies in urban trauma centers had shown as many as 50% of major trauma victims will develop
some degree of hypothermia, with 10% to 15% experiencing severe hypothermia (Gentilello &
Jurkovich, 1996). Nursing care is essential to addressing the particular challenges of trauma
hypothermia; critical care nurses must have an intimate knowledge of the pathology of this
population as well as the skills to recognize, prevent, and treat these patients.
Defining the Problem
In its most general terms, hypothermia is defined as a core body temperature below 35°C.
The traditional research literature and protocols have broken the designation down further into:
mild hypothermia 35°C to 32°C; moderate 32°C to 28°C; and severe below 28°C (Tisherman,
Hypothermia in Trauma
2002). Normally the human body is able to maintain its temperature in a very narrow range
regardless of environment. Heat loss occurs through radiation, conduction, convection, and
evaporation. A person under some type of cold stress may increase their physical activity,
shiver, and increase food intake in an effort to create endogenously the heat necessary to
maintain homeostasis. A severely injured patient is often unable to do any of these (Tisherman,
2002).
During mild hypothermia, changes are subtle; however, as core temperature decreases,
profound and far-reaching effects are seen in all major body systems. The body initially tries to
conserve body heat by increasing metabolic activity and shivering, resulting in metabolic
acidosis (Tisherman, 2002). As cooling progressing, breathing slows, level of consciousness
drops, and with severe hypothermia, cardiac arrhythmias develop (Tisherman, 2002). In her
synopsis of nursing knowledge necessary to face this challenge, Sedlack (1995) states, “Overall
hypothermia complicates trauma care by interfering with ventilation and oxygenation; by
causing vasoconstriction, which obscures arterial assessment and hampers venous access; by
producing coagulopathy and increased blood loss; and by slowing hepatic metabolism and
elimination of drugs” (p. 20-21). Hypothermia decreases kidney ability to reabsorb fluid and
electrolytes resulting in “cold diuresis,” further complicating the clinical picture (Tisherman,
2002). Similar to shock, the process is progressive, starting as a protective function that rapidly
progresses to major organ dysfunction and eventual death.
Sedlack (1995), Tisherman (2002), and Gentilello & Jurkovich (1996) all suggest there
are predisposing conditions, certain injuries, and iatrogenic causes of trauma hypothermia.
Young, elderly, and alcohol-impaired patients are predisposed to hypothermia. Large wounds
such as burns, significant abrasions, and open cavities as well as central nervous system injuries
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Hypothermia in Trauma
predispose patients to hypothermia. Additionally, hypothermia may results from the
interventions commonly used to resuscitate a traumatic patient. Administration of medications
can suppress the body’s ability to maintain heat production metabolically (Tisherman, 2002;
Gentilello & Jurkovich, 1996; Sedlack, 1995). Use of unwarmed intravenous fluids, irrigations,
and lavages as well as the stripping of clothing during assessment can cause hypothermia and
significantly lower the temperature of an already hypothermic patient (Tisherman, 2002;
Gentilello & Jurkovich, 1996; Sedlack, 1995).
Review Process
The purpose of the review is to examine the particular challenges of a critically injured
patient with co-existing or secondary hypothermia. Using the search terms ‘trauma’ and
‘hypothermia,’ computerized searches of the MEDLINE, CINAHL, and Pre-MEDLINE
databases were conducted. The hypothermia search was focused to include all of the possible
sub-headings. The terms were combined and limited to research since 1992, conducted on
human subjects, and published in the English language. This produced 61 articles. Accidental
hypothermia, therapeutic hypothermia, military, pediatric, and laboratory studies were omitted.
With these limits applied, along with the dropping of letters, opinions, and anecdotal case
studies, 41 studies remained to be examined. Twenty-five of these studies were review articles.
Twelve of these studies were primary research. After cross-referencing the reference lists of all
41 studies, as well as texts with chapters addressing hypothermia such as Tomaszewski (2001)
and Tisherman (2002), an additional 3 studies were included in the review.
In order to create a clear picture of research relating specifically to hypothermia
prevention and treatment in trauma patients, several limits were used to omit research from this
review that may have confounded resulting recommendations. Studies that exclusively
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addressed what is termed ‘accidental hypothermia,’ or hypothermia primarily from
environmental exposure, were excluded due to the fact that cold temperatures may be protective
in an otherwise non-injured patient. This creates very different research modalities which do not
apply to a massively injured, exsanguinating patient. Similarly, there has also been a lot of
research, particularly in head trauma, concerning the use of therapeutic hypothermia. Again, this
is a separate research category and falls outside the scope of research concerned with a
traumatically injured patient in critical need of resuscitation, stabilization, and definitive surgical
intervention. Researchers in therapeutic hypothermia have stated more research is needed before
rapid rewarming and aggression treatment is withheld from this population (Tisherman, 2002;
Kirkpatrick, Chun, Brown, & Simons, 1999; Tisherman, Rodriguez, & Safar, 1999). Military
studies were omitted due to the different wounds sustained by this population (landmine injuries,
shrapnel injuries, high velocity gunshot wounds, severe burns, etc.) compared to civilian trauma
patients as well as the distinctive prehospital treatment and transport of military personnel.
Pediatric studies were omitted due to different physiologic needs of children compared to adults.
Laboratory studies and human ‘model’ studies were omitted due to their inability to reproduce
the dynamic environment of trauma resuscitation and the endpoint of failed rewarming, death. A
significant amount of research relating to the best method of temperature measurement has been
conducted; this research was omitted as being beyond the scope of this paper (Fallis, 2002;
Clemence, 2001; Giuliano, Scott, Elliot & Giuliano, 1999). These related areas of research show
that there exists a large body of literature related to this subject; in order to understand
temperature homeostasis in various patient populations, these areas should be examined
separately.
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Discussion of the Literature
The primary research concerning hypothermia in trauma patients was organized into
three general categories for the purpose of analysis: 1) Incidence, 2) Pathology, 3) Prevention
and Treatment. Table 1 includes detailed analysis of each study including objective, design,
methods, sample, setting variables analyzed, results, conclusions, and implications. A series of
meta-analyses, evidence-based practice programs, and state of the science papers will be used to
both comment on the primary research and to synthesize implications of the entire body of
knowledge.
Incidence
Hypothermia can begin to affect patients from the moment of injury; a study in Austria
found that 80 out of 100 patients with minor injuries were hypothermic at the scene when
initially treated by emergency crews (Kober et al., 2001). In order to examine trends in the
incidence, prevention and treatment of hypothermia, several epidemiologic studies were
conducted in the past decade. Three research studies retrospectively analyzed trauma center
records to determine the frequency of hypothermia. Studies varied in size but tended to have
samples representative of the general trauma population. The majority of patients were male,
most received blunt and penetrating injuries, and many were in motor vehicle crashes. Mize,
Koziol-McLain, & Lowenstein (1993) found that only 77% of the patients in their study had
temperature assessed during trauma resuscitation, 10% of which were hypothermic. More
importantly, they found that the more severely injured a patient, the less likely they were to have
their temperature measured. Five years later a smaller study showed similar results; only 40% of
patients had temperature measurement in the emergency department, 33.3% of which were
hypothermic (Shreve, 1998). Both of these studies found a negative correlation between injury
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severity and temperature and a clear association between hypothermia and mortality. The
absence of temperature measurement affects research as demonstrated by Shreve (1998), who
was unable to show a statistical relationship between morality and temperature because none of
the mortalities had a temperature measurement recorded.
Hypothermia is a continuing issue beyond the resuscitation phase. Watts et al. (1999)
found approximately 65% of their patients to be hypothermic on admission to the emergency
department (ED); and lower temperatures correlated with longer ICU and total hospital stays.
On arrival in the intensive care unit (ICU); 52.7% of trauma patients were shown to have a
temperature less than 35°C (Rutherford et al., 1998). Furthermore, this study showed that spinal
cord injuries were associated with high risk for hypothermia and hypothermia was associated
with greater length stay and resource use. The incidence of hypothermia was independent of
month of admission. Other research studies conducted in the past ten years, but not specifically
designed to investigate incidence, offer very similar findings. Bernabei, Levinson & Bender
(1992) found that 46% of trauma laparotomy patients arrived in the operating room (OR) with
temperatures less than 36°C. Watts et al. (1998) found 38% of their patients to have temperature
under 36°C. These studies, in addition to studies with similar design and purpose published in
the decades prior, clearly show that hypothermia continues to be a major issue for trauma
patients and needs to be better addressed by nurses and physicians in their initial stabilization
and continuing treatment of severely injured individuals.
Pathology
Is the low temperature of severely injured patients who eventually succumb to their
injuries simply a sign of the death process as their metabolism progressively fails? Studies
controlling for injury severity have shown that blood loss, fluid requirements, and the presence
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of shock are higher in hypothermic patients (Gentilello & Jurkovich, 1996). Similar to the
studies investigating hypothermia incidence, those addressing the pathology of hypothermia in
trauma patients were conducted in a variety of settings, including emergency departments,
operating rooms, and intensive care units. Primarily these studies address a concept referred to
by Rotondo & Zonies (1997), as the “trauma triad of death,” or by Moore (1996) as “the bloody
vicious cycle.” Active hemorrhage, iatrogenic factors, cellular shock, tissue injury, massive
transfusions, and pre-existing diseases all combine with hypothermia, acidosis, and coagulopathy
to form a lethal physiological state (Moore, 1996). During the early nineties, studies proved this
lethality of hypothermia in trauma laparotomy with as many as 90% of deaths occurring in the
coldest patients, with a four-fold increase in blood loss, and a significant correlation between
hypotension and hypothermia (Bernabei et al., 1992). There has been a large shift in the
understanding of hypothermia over the past decade; the abbreviated laparotomy and damage
control approach have been developed to address this issue specifically (Moore, 1996). It was
hypothesized that the coagulopathies associated with trauma hypothermia are related to blood
transfusions as well as the breakdown in the normal clotting process. Research shows that
standard coagulation assays conducted at 37°C do not adequately reflect the clotting dysfunction
in a hypothermic critically ill patient; and correction of hypothermia alone can correct the
coagulopathies (Gubler, Gentilello, Hassantash, & Maier, 1994). This finding supports the
damage control approach of early transfer to the ICU for aggressive rewarming prior to definitive
surgical closure.
In an attempt to determine which patients should receive the abbreviated laparotomy with
damage control approach and aggressive rewarming treatments, Cosgriff et al. (1997) strove to
create a formula for predicting life-threatening coagulopathies in trauma patients receiving
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transfusions. They found a systolic blood pressure less than 70mmHg, a pH less that 7.10, a
temperature less that 34°C, and ISS greater than 25 was associated with a 100% mortality rate
(Cosgriff et al., 1997). These life-threatening coagulopathies were investigated in a similar study
with larger sample; patients with temperature below 34°C have significant alterations in platelet
and clotting enzyme function, lower blood pressures and heart rates, and increased mortality
(Watts et al., 1998). Severe trauma is invariably associated with large amounts of tissue damage,
resulting in the release of thromboplastin, leading to hypercoagulation and tissue hypoxia;
“…while hypothermia does affect coagulation, the hypercoagulability that is the result of severe
trauma seems to allow the body to compensate for some of this hypothermic alteration” (Watts et
al., 1998, p. 853). Watts et al. (1998) found that their coldest patients’ blood was able to clot but
at a much slower rate. When controlling for injury severity, Watts et al. (1998) found that
hemorrhage may well lead to hypothermia but clinically hypothermia seems related to shock
rather than merely volume loss. These findings are limited, however, by the fact that only
prehospital fluid requirements were included in the study and the very short transport times for
all included patients.
Despite this limitation or others in individual studies, the mortality rates associated with
hypothermia in trauma prompted Gentilello & Jurkovich (1996) to suggest a very different
severity definition for guidance of treatment: mild hypothermia 36°C to 34°C; moderate
hypothermia 33.9°C to 32°C; and severe hypothermia below 32°C. This change has not been
adopted by the entire research or practice literature but does reflect a valid point; declining
temperature in a critically injured patient in a major warning sign of impending complications.
Aggressive treatment is needed. All of the authors urge the conduction of large, multi-center
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studies to continue to better understand these key physiological variables; this will help nurses
and physicians predict which patients will suffer “the bloody vicious cycle.”
Another frontier of understanding the pathology of hypothermia in trauma patients is the
relationship between hypothermia and cellular levels of adenosine triphosphate (ATP).
Seekamp, von Griensven, Hildebrandt, Wahlers, & Tscherne (1999) compared trauma patients,
55% of whom were hypothermic, to patients undergoing voluntary coronary bypass and knee
surgery. Therapeutic hypothermia in elective surgery preserves ATP storage and maintains
aerobic metabolism thus reducing ischemia; however, hypothermia in trauma patients is caused
by insufficient heat production due to depletion of ATP stores under anaerobic conditions
(Seekamp et al., 1999). This study found that low plasma levels of ATP combined with
hypothermia predispose patients to severe complications, specifically multiple organ
dysfunctions. The implications of this study and other animal studies investigating the same
process could eventually result in the administration of ATP-MgCl2 during trauma resuscitation
in order to reverse cellular dysfunction; Seekamp et al. (1999) suggest the need for considerable
research before this is added to the treatment options presently available.
Prevention & Treatment
Prevention and treatment of hypothermic trauma patients depend on the severity of
injury, severity of hypothermia, and resources available at the scene and receiving hospital.
Treatment options can be classified as: 1) passive external rewarming; 2) active external
rewarming; and 3) active core rewarming. The three categories are not exclusive but rather build
upon each other as hypothermia becomes more severe; all three levels of rewarming are
necessary. Nurses and physicians who care for trauma victims not only need an understanding of
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the pathology of hypothermia, they need to understand the basis and underlying logic for
choosing prevention and treatment methods in different situations.
Passive External Rewarming
All trauma patient should receive hypothermia prevention and treatment starting in the
field and continuing until they are fully rewarmed (Tisherman, 2002). Passive external
rewarming refers to several basic measures: wet clothing removal; reducing airflow over the
body to reduce heat loss due to convection; raising transport unit, trauma resuscitation, and
emergency room temperatures; covering the head, and wrapping in warm blankets (Peng &
Bongard, 1999). There has been little research into the merits of blankets, room temperature,
and convection alone; however, there have been various studies of their effectiveness on patients
in surgery under general anesthesia (Goodlock, 1995). This is a very different population and
findings may not fully apply to the specific difficulties faced by trauma patients. Intraoperative
studies have demonstrated the equal effectiveness of warm cotton blankets and metallic plastic
blankets (Goodlock, 1995); however, the aluminum ‘space blankets’ do not conform well to
body surfaces resulting in convective and conductive heat loss (Gentilello & Jurkovich, 1996).
Passive external rewarming relies on the patient’s own rewarming mechanisms to generate heat;
this requires tremendous energy and oxygen consumption, which an injured patient often does
not have to spare (Gentilello & Jurkovich, 1996). Specifically, passive rewarming of a patient
with intact thermoregulation may result in anaerobic metabolism, lactic acidosis, and significant
cardiopulmonary stress; anesthetic and neuromuscular blocking agents can minimize this process
but do not treat the clotting and cardiac issues that also occur in hypothermia (Gentilello, 1995).
Passive rewarming is still the easiest and least expensive method available.
Active External Rewarming
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Active external rewarming refers to the use of heating blankets, convective air blankets,
and radiant warmers. In addition to increased rewarming rates with active external rewarming,
Kober et al. (2001) showed that ‘resistive heating,’ their term for active rewarming, during
prehospital transport increases thermal comfort, reduces pain and anxiety, and improves patient
satisfaction with care. Their study only addressed patients with minor injuries; however, the
patients supplied with an electric and cotton blanket showed oral temperature increases of 0.8°C
per hour compared to the patients covered in blankets alone who cooled 0.4°C per hour during
transport. Kober et al. (2001) found that even these patients with minor injuries were at risk for
hypothermia if not actively rewarmed; the mean core temperature of the 100 patients was 35.5°C
upon admission to the hospital. Much of the research on efficacy of different heating methods
such as fluid-filled blankets and radiant warmers took place more than ten years ago. Synopses
of the results of these studies are available in many different state of the science papers as well as
critical care texts.
Watts et al. (1999) strove to examine the efficiency of rewarming methods that have been
used by prehospital crews for years with or without research proving their usefulness. Although
two of their treatment groups included active internal rewarming with warmed intravenous
fluids, this study actually found that patients receiving hot packs under the axilla, behind the
head, and on the abdomen, retained more heat. Watts et al. (1999) suggest that this simple active
rewarming method is one of the least used interventions in prehospital and resuscitation studies
despite its effectiveness.
Convective air warmers, otherwise known as forced-air rewarming blankets, are in use in
many emergency departments throughout the country. These devices use a disposable plastic or
paper blanket with slits on the patient side to create a warm air space around the patient.
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Properly creating a 43°C microenvironment around the patients, the temperature necessary to
actively stop heat loss, requires a substantial portion of the body surface be covered, limiting
access to the patient (Gentilello & Jurkovich, 1996). A recent nursing-centered study by Cohen,
Hayes, Tordella, & Puente (2002) found this limitation to be a major drawback of this method of
rewarming. Their patients received one of three interventions: 3 pre-warmed (105°C) cotton
blankets; a reflective blanket with head covering over 1 pre-warmed cotton blanket; or a forcedwarm-air inflatable blanket. Cohen et al. (2002) found no significant difference in rewarming
rates between the three methods. More important for nursing staff was the finding that the
forced-warm-air blanket was difficult to work around during resuscitation; this method received
the worst scores on ease of use, convenience, and access. Nurses also reported that heated cotton
blankets needed frequent changing and reflective blankets with head coverings could not be used
if the patient was on a backboard. Cohen et al. (2002) suggest that since each rewarming method
shows similar results, nurses should use the intervention most readily available and most
effective for the particular patient and setting. For example, Peng & Bongard (1999) suggest that
in trauma patients with alcohol intoxication, forced-air rewarming may be more effective due to
peripheral vasodilation, but in shock may be no more efficient than cotton blankets due to
peripheral vasoconstriction.
Active Core Rewarming
Aggressive active external rewarming should not be used as the sole intervention in
severe hypothermia due to afterdrop and aftershock. Afterdrop refers to a core temperature drop
of 2° to 3°C during the first 30 minutes of external only rewarming which has been associated
with ventricular fibrillation; cold, acidotic, blood, returning to the heart can cause cardiac
collapse (Sedlack, 1995). During hypothermia, intravascular fluid is shifted into the core; the
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kidneys respond by excreting an excess of fluid, a process known as “cold diuresis” (Sedlack,
1995). When surface tissues are rewarmed first, they vasodilate, creating a relative
hypovolemia; this results in hypotension (Sedlack, 1995). Therefore, passive rewarming and
active external rewarming must serve as adjuncts to care when a clinician is faced with a
severely hypothermic trauma patient. The core of the body must be warmed first. Leben, Tryba,
Bading, & Heuer (1996) confirmed this when they found infusing trauma patients with a fluid
warmer and warming with convective blankets prevented afterdrop, reduced length of intubation,
and length of stay in the intensive care unit.
Active core rewarming refers to methods including airway rewarming; heated peritoneal
or pleural lavage; infusion of warmed intravenous fluids and blood products; and extracorporeal
circulatory rewarming. Airway rewarming is considered a means of preventing respiratory heat
loss, not a method of core rewarming; it has shown little efficiency when used alone (Gentilello
& Jurkovich, 1996). No studies have been conducted in recent years comparing peritoneal or
pleural lavage to other methods; however, both are used extensively to rewarm trauma patients,
especially with moderate or severe hypothermia (Gentilello & Jurkovich, 1996). Warmed
intravenous (IV) and blood products are not only an excellent way to prevent heat loss; they
actively warm a hypothermic patient. As mentioned above, Leben et al. (1996) reconfirmed this
already accepted method. The length of tubing and infusion rate can have significant effects on
the actual delivered temperature of fluid. Handrigan, Wright, Becker, Linakis, & Jay (1997)
showed that adequately warmed fluids for IV or lavage is achievable by: 1) preheating fluid to
60°C when using long segments of tubing; 2) preheating fluid to 40°C when using short
segments of tubing; and 3) administering fluids in rapid boluses rather than continuous drips.
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The use of warm IV fluids as a warming technique; however, is limited by the fluid
requirements of the patient (Gentilello & Jurkovich, 1996). In their early investigation or
extracorporeal rewarming, Gentilello, Cobean, Soderberg, & Jurkovich (1992) were able to
warm hypothermic patients to 35°C in an average of 39 minutes rather than 3.23 hours from the
same start point. In addition, they found that this rapid reversal of hypothermia reduced organ
failure, fluid requirements, ICU stay, and increased survival significantly. Gentilello et al.
(1992) had developed the used of Continuous Arteriovenous Rewarming (CAVR); this method is
similar to arteriovenous hemofiltration with the addition of a fluid-warmer in the circuit.
Gentilello, Jurkovich, Stark, Hassantash, & O’Keefe (1997) expanded on these findings by
comparing hypothermic trauma patients treated with CAVR to patients receiving warm IV fluids,
airway rewarming, convective air blankets, and head covering. They were able to show that the
patients rapidly rewarmed with CAVR had less fluid requirements, a much lower risk of early
mortality, fewer organ failures, and lower oxygen requirements. Gentilello et al. (1997) did find
a higher incidence of acute respiratory distress syndrome and longer intensive care unit stay in
CAVR patients; however, they felt this was because more of the CAVR patients survived initial
resuscitation and later succumbed to their injuries. Most importantly, this method warms the
core blood supply without the dangers of afterdrop or aftershock.
Extracorporeal rewarming using cardiopulmonary bypass has been the standard of
treatment for severely hypothermic patients for some time; however, this method requires a
degree of anticoagulation that is often ill advised for a patient already faced the trauma triad of
death (Lapointe & Von Rueden, 2002). Despite this, in patients with deep hypothermia and
cardiac arrest, it is still the treatment of choice and does not seem to cause long-term effects
(Walpoth et al. (1997). Patients who require these aggressive active internal rewarming methods
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are at the greatest risk for developing severe cardiac arrhythmias and the coagulopathies
associated with acidosis and hypothermia; this level of care requires highly trained, extremely
vigilant nursing at all times. Nurses in all clinical areas have the ability to recognize
hypothermia and begin measures to prevent heat loss; passive external, active external, and
active internal rewarming methods should all be familiar in order to treat the particular
challenges of individual patients.
Conclusions
The research addressing hypothermia in traumatically injured patients offers a successful
example of research and practice integration with continuous improvement of techniques over
time. As trauma incidence has increased, clinical practitioners and researchers have responded.
Studies showing high levels of mortality in hypothermic trauma patients resulted in investigation
of the intricacies of the pathology of hypothermia, comparison of the utility of various
prevention and treatment methods, and development of completely new forms of rapid core
rewarming. The basic premises of how and why the body reacts to hypothermia are fairly well
understood; and the methods of rewarming are approaching the physiological limits of the
patients. The body of evidence is most lacking in three main areas: 1) sample size, location, and
continuity of care; 2) variability of injury severity and measurement; and 3) temperature
measurement variations.
Although several large, multi-center studies are referenced in the literature, they were
conducted more than 15 years ago. Almost all of the studies in this review had sample sizes
smaller than 100 and most fewer than 15 per treatment group. Larger samples are needed to give
statistical power and clinical significance to the research. Also, considering the evidence given
by Mize et al. (1993) that many trauma patients are not having their temperatures assessed
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despite severe injuries and hypothermia, updated multi-centered research investigating the
progress in addressing this issue is needed. Moreover, almost none of the studies published
concerning trauma hypothermia specifically focuses on the nursing-centered care of hypothermia
prevention and treatments during trauma resuscitation. To synthesize data from the entire body
of research one must make conclusions based on the temperatures of patients when transferred to
the operating room or intensive care unit.
In addition to a lack of studies focusing specifically on trauma resuscitation, few studies
sought, within their design, to track the temperature management of patients from the field
through their entire treatment process. To aid in clinical and policy decisions concerning
hypothermia prevention, the areas of greatest danger must be identified and best means of
addressing temperature loss in that arena delineated. Although not a research study, Aragon
(1999) offers an excellent example of this process. Specific results have yet to be published;
however, in a major facility investigation and improvement program in Orlando, Florida, a team
was created to study every area of care where hypothermia can be recognized and treated from
the prehospital teams, through the emergency rooms, radiology suites, operating rooms, and
critical care units (Aragon, 1999). New protocols were written and measures were taken to
insure they were followed, such as posters reminding staff of hypothermia issues. Specifically
this study recommended the creation of critical checklists, including documentation of
temperature along with other vital signs at every point in a trauma patients care (Aragon, 1999).
In addition to location variation among research studies, the samples in this review had
wide ranges and methods of measuring injury severity, thus limiting the application of findings
to the creation of protocols for use with all patients. Two studies used the APACHE II scoring
system; however, this system only accounts for the lowest temperature in a 24-hour period and
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therefore does not measure progressive heat loss or gain in the resuscitation phase (Rutherford et
al., 1998; Gubler et al., 1994). Most studies used the Injury Severity Score (ISS), a system
assigning each anatomical injury an abbreviated injury score (AIS), that when combined
provides an overall score for patients with multiple injuries.
Its weaknesses are that any error in AIS scoring increases the ISS error, many different
injury patterns can yield the same ISS score and injuries to different body regions are not
weighted. Also, as a full description of patient injuries is not known prior to full
investigation & operation, the ISS (along with other anatomical scoring systems) is not
useful as a triage tool. (Baker, S. P. et al., 1974, as referenced by Trauma Scoring)
In addition to these internal weaknesses, the mean ISS score varied widely among the studies in
this review from 8.9±9.6 to 32±8.3 (see Table 1 for details). The studies focusing on pathology
tended to address patients with higher ISS scores than the studies addressing prevention and
treatment. Temperature was found to correlate negatively with ISS (Mize et al., 1993; Shreve,
1998); and when stratified by ISS, hypothermic patients have significantly higher mortality rates
than patients with the same ISS who remain warm (Gentilello, 1995). Additionally, Watts
(1998) found the Glasgow Coma Score (GCS) and Revised Trauma Score (RTS) also correlate to
hypothermia. ISS is a measure of anatomic injury; Revised Trauma Score is a measure of
physiologic derangement; Bernabei, et al., (1992) found trauma score to be a much better
predictor of hypothermia than ISS. Since all levels of ISS score found deleterious effects of
hypothermia, it would be useful to take the research literature closer to clinical reality and use
the Trauma Score-Injury Severity Score (TRISS) system as a measure consistently. The TRISS
system integrates ISS, GCS, and blood pressure (Trauma Scoring); this would allow for clearer
comparisons between research study designs, samples, and settings.
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The initial recognition of hypothermia is likely to be made by nurses during the
assessment of vital signs. Research has shown significant problems with consistent
measurement practices ranging from complete omission to varying results from different
measurement techniques. The reviewed research studies used oral, rectal, airway, tympanic, and
pulmonary artery temperatures; these variations in the literature make substantive conclusions
somewhat difficult. An entire separate body of evidence exists concerning the best method of
temperature assessment (Fallis, 2002; Clemence, 2001; Giuliano, Scott, Elliot & Giuliano, 1999);
however, during the initial stages of trauma resuscitation oral, rectal, and tympanic temperatures
are most often used (Peng & Bongard, 1999). Only research conducted in the operating room or
ICU usually has the luxury of the ‘gold-standard’ pulmonary artery temperature.
The variations across the body of research also become a challenge when one seeks to
create clinical protocols relating to treatment and prevention at various temperature ranges.
Some of the research defines a temperature less than 36°C as hypothermic, some less than 35°C.
Most of the literature considers temperatures over 32°C mild hypothermia. Gentilello &
Jurkovich (1996) and Gentilello (1995) suggest narrowing the ranges for treatment modalities
significantly to 36° to 34°C as mild, 33.9°C to 32°C as moderate, and below 32°C as severe.
The lethal reactions to temperatures below 32°C have been clearly delineated in the trauma
hypothermia research. These recommendations are not reflected throughout the research
literature, especially research designed specifically for consumption by nurses (Lapointe & Von
Rueden, 2002; Cochrane, 2001; Fritsch, 1995). As research is focused on trauma resuscitation
and nurses’ roles in initial recognition and treatment of hypothermia, the nursing literature must
be updated to reflect the most current understanding of pathology and recommendations of
researchers and clinicians.
Hypothermia in Trauma
21
This integration of research with practice can be seen in the Hospital of the University of
Pennsylvania Trauma Center protocols for hypothermia treatment; this policy insists that all
trauma patients must have temperature assessed within 30 minutes of arrival to the trauma bay
(Reilly, Gracias, Fitzpatrick, 1999). The policy has clear and specific recommendations for each
level of hypothermia severity including aggressive prevention measures for all patients, active
external warming for temperatures less than 36°C, active internal warming for temperatures less
than 35°C, and external veno-venous rewarming for temperatures less than 34°C (Reilly,
Gracias, Fitzpatrick, 1999). In keeping with the recommendations of the research literature, this
policy also has specific recommendations for measures in each phase of care from trauma bay, to
radiology, to OR, and ICU (Reilly, Gracias, Fitzpatrick, 1999).
The currently accepted standard of care is to prevent and treat hypothermia from the
initial scene, through the primary assessment during trauma resuscitation, and beyond into
stabilization. The advanced trauma life support (ATLS) guidelines from the Committee on
Trauma of the American College of Surgeons continually urge the importance of temperature
control and aggressive efforts to avoid and treat hypothermia, including the specific trauma
hypothermia temperature range definitions suggested by the research literature (Committee on
Trauma, American College of Surgeons, 1997). The Society of Trauma Nurses also trains nurses
to begin prevention and treatment of hypothermia as soon as the primary assessment is
completed (Society of Trauma Nurses, 2003). They offer warming strategies by department and,
in the hemorrhagic shock chapter, specifically address the pathophysiologic consequences of
hypothermia. The research literature, the policies of leading hospitals, and the recommendations
of trauma surgeon and nursing organizations all stress the importance of prevention and
treatment, early and continually, throughout patient care.
Hypothermia in Trauma
22
Hypothermia has been clearly associated with coagulopathies, hypotension, acidosis, and
high mortality. More remains to be understood about the effects of hypothermia in trauma on the
physiology of patients; the future may see the use of therapeutic hypothermia for head trauma,
ATP treatment to reverse adverse effects, and aggressive rewarming taking place early in
resuscitation. Trauma care clinicians, especially nurses, will continue to be at the forefront of
prevention, recognition, treatment, and research in hypothermia, thus pushing back the definition
of survivable injury.
Hypothermia in Trauma
23
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Author’s Note
Frederick D. Watters, BSN student, School of Nursing, University of Pennsylvania.
The author would like to thank Dr. Therese Richmond, Associate Professor of Trauma &
Critical Care Nursing, at the University of Pennsylvania School of Nursing, who served as
faculty advisor to the project, guided the topic selection, and gave editorial and content advice in
the process of writing.