Therapeutic Hypothermia

NUR 437 Nursing Research: The Beneficial Effects of Therapeutic Hypothermia

According the statistics from the American Heart Association (2012), when electrical impulses to the heart suddenly become uncoordinated, causing the immediate cessation of the heart to function, this is considered a cardiac arrest. Cardiac arrest that occurs outside of the hospital has an incidence of 359,400 with a survival rate of 9.5 % (American Heart Association (AHA), 2012). In absence circulation, neurological injury occurs from the lack of oxygen delivered to the brain (Deckard & Ebright, 2011). This disruption of oxygen can cause a cascade of events that include hypoxia, cellular death, the activation of the inflammatory response, and cerebral edema. The continuation

of cellular death and the activation of the inflammatory response leads to exacerbation of cerebral edema (Deckard & Ebright, 2011).

Therapeutic hypothermia has been an identified intervention that will slow the inflammation process and improve neurological outcomes for patients experiencing out of hospital cardiac arrest (Bernard et al., 2010). Therapeutic hypothermia is defined as the controlled induction of reducing a patient’s core body temperature below 34° C while managing the body’s compensatory mechanism by prevent shivering (So, 2010). The integrity of the process is the accurate measurement of the core body temperature, which can be obtained if the probe is place in the central venous, bladder, rectal, or esophageal (So, 2010). Therapeutic hypothermia occurs in the following phases: induction, maintenance, and rewarming (Deckard & Ebright, 2011). The induction phase begins when a health care professional lowers the patient’s core temperature to the target temperature. (Deckard & Ebright, 2011). Cooling methods include a combination of external cooling methods such as, surface cooling with ice packs and cooling blankets, as well as internal cooling methods such as, catheter-based technologies for the infusion of cold fluids (Mooney et al., 2011). During the induction phase it is important for the nurse to pay close attention to the patient’s blood pressure and fluid balance, as

induction can cause cold diuresis and a decrease in antidiuretic hormone levels. The maintenance phase can last from 12 to 24 hours beginning the time the target temperature has been reached. The rewarming phase begins after the end of the maintenance phase and can last from 12 to 24 hours (Deckard & Ebright, 2011). It is crucial that the nurse monitors the patient closely as the rewarming phase can lead to electrolyte shifts and hypoglycemia (Deckard & Ebright, 2011). Therapeutic hypothermia is currently the only intervention that can protect the neurological function of the brain leading to more positive outcomes when utilized (Kowalik et al., 2014). The purpose of paper is to evaluate the beneficial effects of therapeutic hypothermia.
Study One: With or Without Therapeutic Hypothermia
A retrospective study completed by Kowalik et al.

(2014), collected data for the control group using historical data for 37 adult patients hospitalized at the same center from 2009 to 2011. Whereas the group that received the intervention was collected on 28 adult patients treated from 2011 to 2013. Inclusion into the study required a systolic blood pressure above 80 mm HG, cardiac arrest time and recruitment time of less than four hours, initial Glasgow Coma Scale (GCS) of < 8, and an age older than 18. Exclusion criteria included active bleeding, unconsciousness prior to the cardiac arrest, presence of any disease that diminished normal life expectancy, and an initial body temperature of less than 30°C. The study monitored temperature using an esophageal temperature probe with a target temperature set at 33°C. The maintenance phase lasted for 36 hours. During the rewarming phase the core temperature was increased 0.01°C per hour. Cognitive function was assessed using the Cerebral Performance Categories (CPC) scale and Glasgow Coma Scale. Assessments were performed by a qualified neurologist. For the intervention group, the assessment was immediately after the complication of the intervention and the discontinuation of sedation and analgesia medications. The control group was assessed after the cessation of anesthetic administration. A CPC score of 1 or 2 and a GCS of 13 or above were associated with a favorable neurological outcome. All participants scored a favorable

CPC score at discharge. Patients that received the intervention scored better on the GCS than the control group; 15/16 and 13/15 respectively (Kowalik et al., 2014). Although there was not a significance difference in the outcomes related to physical capacity and independent functioning in survivors of cardiac arrest, Kowalik et al. (2014) found that the results of the study suggest a better survivor rate when therapeutic hypothermia is a part of the treatment plan. The group receiving the therapeutic hypothermia had a mortality rate of 35.7% versus the control group, where therapeutic hypothermia was not an intervention in the plan of care, indicating a mortality rate of 45.9% (Kowalik et al., 2014).
Study Two: Initiation of therapy
Bernard et al. (2010) completed a prospective random controlled trial evaluating the effectiveness of early induction of hypothermia by first responders compared to patients that received the induction at the hospital. This study was started October 2005 and lasted until November 2007, where 118 participants received paramedic initiated therapy versus 116 participants that initiated cooling at the hospital. Patients were selected based on a systolic blood pressure of over 90 mm HG, initial cardiac rhythm of ventricular fibrillation, a cardiac arrest time of less than 10 minutes, and an age of 15 or older (Bernard et al., 2010). Exclusion was based on ability of intubation, reliance of others to perform activities of daily living prior to the cardiac arrest and a temperature of less than 34°C. Target temperature for patients was set at 33°C and maintained for 24 hours. Core temperature was evaluated by paramedics using temporal probes while the hospital measured temperature using a bladder temperature probe. This study collected data from ten government hospitals and two private hospitals. All healthcare personnel acted on a protocol that followed the recommendations of the Australian Resuscitation Counsel (Bernard et al. 2010). The instrument used to determine and compare results was Mann-Whitney rank sum test using the statistical software STATA. There was a slight favorable outcome with hospital initiated cooling of 52.6% compared to paramedic imitated cooling of 47.5%. The study was terminated before the required sample size was obtained due to futility. The researcher concluded that patient functional outcome did not improve in patients that received therapy initiated by a paramedic than the control group initiating therapy in the hospital.
Study Three: Male versus Female
Greenberg et al. (2014), completed a retrospective observational cohort study with abstract data from an existing database beginning January 2005 to September 2013. The study attempted to differentiate positive outcomes based on sex. The inclusion criteria included a GCS of < 6, systolic blood pressure above 90, age 18 or older and less than 60 minutes from out of hospital cardiac arrest to the return of spontaneous circulation. Participants were excluded if initial body temperature was less than 30°C, persistent hypoxia with oxygen saturation of less than 85% for longer than 15 minutes, know active bleeding or coagulopathy, and a medical illness prior to cardiac arrest that would impeded them from recovery. Target temperature was set at 33°C and maintained for 24 hours. Participates were rewarmed 1°C per every four to six hours. Patients were assessed using Glasgow-Pittsburgh CPC. There were 198 male participants and 132 female participants, 60% and 40% respectively. The researcher found that men were more likely to have a ventricular tachycardia or ventricular fibrillation as an initial rhythm as opposed to women that were more likely to present with an initial rhythm of asystole (Greenberg et al. 2014). Women were found to reach target temperature at a faster rate than men. Overall there was not a significant difference in crude mortality rates in men than women; however it is important to note that once confounders were adjusted of patients receive therapeutic hypothermia females were less likely to die than males (Greenberg et al. 2014).
Review of Literature
The target temperature for the intervention, therapeutic hypothermia, in all three studies was set at 33°C. Both Kowalik et al. (2014) and Greenberg et al. (2014) shared the exclusion criteria of initial body temperature of 30°C and active bleeding. However, Bernard et al. (2010) excluded participants with a slightly higher initial body temperature of 34°C and did not mention active bleeding as a part of the exclusion criteria. Kowalik et al. (2014) and Greenberg et al. (2014) used the GCS as an item for inclusion, Greenberg et al. (2014) allowed for a lower score of less than or equal to six compared to Kowalik et al. (2014) who set the score at less than or equal to eight. Bernard et al. (2010) did not include this tool in the criteria. Bernard et al. (2010) and Greenberg et al. (2014) set the standard for the systolic blood pressure at greater than 90 mm Hg, whereas Kowalik et al. (2014) set the requirement at greater than 80 mm Hg. Bernard et al. (2010) had the biggest variance of temperature measurement as paramedics were using different instruments than those at the hospital. Their study also included many different hospitals which would also allow for variance in calibration in instruments as well as age and model of the instrument. Kowalik et al. (2014) had the smallest same size of 65 and the looked at data from different time parameters. The control group, not receiving therapeutic hypothermia, had data set from 2009 to 2011, while data with participants receiving therapy from 2011 to 2013. Major pharmacological developments could have impacted the outcomes between these test groups. Recommendations for this study would be increase sample size and compare data from the same time period. Greenberg et al. (2014), had the largest sample size of 330 total participants and the data spanned over the longest time starting January 1, 2005 to September 19, 2013. The instrument used to measure temperature was not mentioned, which could be interpreted as the use of different tools. Not stating the instrument questions the consistency of data that reflected females obtaining a target temperature faster than males (Greenberg et al., 2014). Bernard et al. (2010) had the best evidence as it was a prospective randomized control trial. It would have been impossible to conduct this study in blind manner, as paramedics responding needed to know how to commence treatment. This study could be strengthened if the sample size was larger, the hospitals used the same model of instruments, as well as a standardization of temperature measuring tools.
Conclusion
When implemented, the use of therapeutic hypothermia has a positive outcome for patients compared to those that do not receive the intervention (Kowalik et al., 2014). The previously mentioned studies suggest that there is not a significant increase in positive outcomes if the cooling is initiated by first responders or if the patient is male or female.