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Hypothermia has been shown to have neuroprotective effects and may have benefit in the treatment of head injuries. However, it is a controversial treatment in traumatic brain injury, and to date, there are no specific recommendations for its use. This article examines six research studies investigating the use of hypothermia as a treatment in patients with traumatic brain injury. All studies were prospective trials and compared a controlled normothermia group with a hypothermia group. Studies were compared by sample population, methods of hypothermia, outcomes, and conclusions. The leading variable in each study was hypothermia. However, each study used a different method of cooling, goal temperature, and duration of cooling. Through the comparison of these studies, a recommendation for change in practice cannot be made. Nevertheless, there may be benefits to hypothermia in traumatic brain injury, and suggestions for future research are identified.
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Each year, in the United States, 1.4 million people sustain a traumatic brain injury. Of this number, 235,000 individuals are hospitalized and survive, with approximately 80,000 to 90,000 experiencing long-term disability. Traumatic brain injury is responsible for 50,000 deaths per year (Centers for Disease Control and Prevention, 2004). Traumatic brain injury encompasses primary and secondary injuries. The damage incurred at impact is referred to as primary injury. Secondary injury is a biochemical and cellular response to the primary injury that begins within minutes to hours of the initial damage. Secondary injury is global and harms tissue that was not involved in the primary injury. It is the amount, severity, and frequency of secondary injury that leads to widespread tissue damage and poor neurological outcomes (Dutton & McCunn, 2003). In the first 24 hr after injury, hypocapnia, hypotension, hyperglycemia, hypoxia, acidosis, intracranial hypertension, and seizures may all occur (Jeremitsky, Omert, Dunham, Protetch, & Rodriguez, 2003). These secondary injuries cause significant neurological damage in part by affecting brain oxygenation. Accordingly, it is vital to manage these secondary injuries immediately to prevent permanent damage (Dutton & McCunn, 2003).
The international medical community has established guidelines for the treatment of traumatic brain injury. These guidelines depict the current standard of care for the treatment of these patients (Brain Trauma Foundation, 2007). Although these guidelines are followed as the first line of treatment, many other experimental strategies are employed to decrease secondary injury, including hypothermia.
The Effect of Hypothermia
The use of hypothermia as a treatment of traumatic brain injury remains controversial. The definition of induced mild hypothermia varies between research studies, but is generally considered cooling to a temperature of 32[degrees]C-35[degrees]C. The Brain Trauma Foundation classified hypothermia as a class III level of evidence. Although it appears to provide benefits, there is not enough research available to make formal recommendations on its use (Brain Trauma Foundation, 2007). It is thought that hypothermia has neuroprotective effects and will prevent or minimize the effects of secondary brain injury. Hypothermia protects the brain by inhibiting massive depolarization in the brain and the release of glutamate and aspartate. Hypothermia, therefore, stabilizes the blood-brain barrier and prevents cell death. It also decreases cerebral metabolic rate, with a resultant decrease in carbon dioxide and lactate buildup. Moreover, hypothermia may prevent uncoupling of the metabolic supply demand regulation and prevent loss of cerebral autoregulation (Wright, 2005). Thus, although still considered a controversial treatment, many institutions employ hypothermia as treatment for the prevention of secondary brain injury (Brain Trauma Foundation, 2007).
Advanced practice nurses, bedside nurses, and physicians are responsible for creating treatment plans for this population of patients and therefore must have knowledge of the latest research. There has been a marked increase in the research surrounding hypothermia as a treatment option due to its potential to improve patient outcomes. The advanced practice nurse on the neurosurgery team is often responsible for the acute management of traumatic brain injury. Advanced practice nurses are vital in exploring the latest research and potential treatments for these patients (Freeborn, 2004).
To identify research articles, a search was performed using Medline, CINHAL, Embase, and PubMed. Key words used alone and in combination were hypothermia, traumatic brain injury, and brain oxygenation. Forty-three primary research articles from 2000 to 2006 written in English were reviewed. Four research studies were identified based on these criteria for selection: (a) inclusion of controlled trials using therapeutic hypothermia for at least 24 hr versus normothermia in adults with traumatic brain injury and (b) outcomes measured by the Glasgow Outcome Scale (GOS). Variables measured were intracranial pressure (ICP), cerebral perfusion pressure (CPP), arterial blood pressure, continuous temperature, and management appropriate for traumatic brain injury. A fifth study was identified by the other researchers as a landmark hypothermia study and was therefore included in the analysis. The last study included did not have a normothermia control group; rather, it compares long-term mild hypothermia to short-term mild hypothermia.
Several meta-analyses have explored the possibility of hypothermia as a beneficial treatment in traumatic brain injury. The most recent meta-analysis examined 14 clinical trials of comparable groups and suggested that hypothermia reduces mortality and results in favorable neurological outcomes when maintained for greater than 48 hr. In addition, the greatest improvements in outcome were found when patients were evaluated 1 to 2 years after injury rather than at 6 months. It also appears that the patients who respond best to hypothermia are those who respond well to standard measures of ICP control, excluding barbiturate therapy (Peterson, Carson, & Carney, 2008). Although the meta-analysis was not able to make a recommendation for the use of hypothermia, its results recognized the potential of the therapy. This article will further explore the topic and compare and analyze the mentioned research studies and discuss the implications of hypothermia as a treatment on nursing practice.
Analysis of Research
Six studies were compared to explore the effects of hypothermia on neurological outcome after traumatic brain injury. Clifton et al. (2001); Gal, Cundrle, Zimova, and Smrcka (2002); Marion et al. (1997), Polderman, Tjong Tjin Joe, Peerdeman, Vandertop, and Girbes (2002); and Jiang et al. (2006) evaluated the effects of hypothermia on patient outcome in the traumatic brain injury population with intracranial hypertension. Shiozaki et al. (2001) looked at the effect of hypothermia on neurological outcome in patients with normal ICE Although it examines a slightly different aspect of brain injury, it is comparable with the other studies and provides a contrast to high ICE The study of Shiozaki et al. used the same methods of treating traumatic brain injury; however, they chose to include patients who did not have high ICP in the hypothermia group. This was notable because the study of Shiozaki et al. demonstrated the effect of hypothermia on patients with normal ICP.
Selection of Patients
In each study reviewed, patients were chosen on admission to the hospital. Inclusion criteria between the studies were comparable, with minimal difference between the selection processes. Patients were accepted if they had a closed head injury and Glasgow Coma Scale (GCS) of 3 to 8. All studies accepted patients aged 16 to 65 years, except the study by Marion et al. (1997), which accepted patients up to 75 years old, and by Shiozaki et al. (2001), which included one patient younger than 16 years.
Exclusion criteria in all six studies included clinical brain death, prolonged hypoxia or hypotension, a gunshot wound, pregnancy, an undetermined time of injury, inability to begin cooling within 6 hr, organ failure of another system, or normal findings on a computerized tomography (CT) scan. The sample populations were comparable across studies. The study by Shiozaki et al. (2001) was the exception and also excluded patients who were unable to maintain their ICP below 25mm Hg on admission despite conventional therapies. The selection of patients was similar between the groups and did not affect the results.
Comparison of Patient Population
The sample population across the six studies was equivalent in terms of age. The mean age of patients in both the normothermia and hypothermia groups was 31 to 42 years and was not a statistically significant variable. Significantly more men participated in the studies than did women, a fact which is reflective of the greater traumatic brain injury population where males are twice as likely as females to sustain an injury (Centers for Disease Control and Prevention, 2004).
All studies used GCS to measure neurological status of patients on admission and for continued assessments throughout the studies. The scale was defined and used in the same manner for each study, which eliminated error in measuring neurological status. With the exception of the study of Gal et al. (2002), the other studies acknowledged differences in the severity of GCS by comparing the hypothermia and normothermia groups as a whole and as subclasses of patients with a GCS of 3 or 4 and 5 to 8. A lower GCS is indicative of more severe injury and thus should be looked at separately from the higher scores. By making this distinction, the studies looked at the effect of hypothermia on degree of injury.
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