Therapeutic Hypothermia Research Paper

Therapeutic Hypothermia for Cardiac Arrest
Jaime Bromley
Jefferson College of Health Sciences
Hypothermia is a decrease in the core temperature below 35 degrees Celsius or 95 degrees Fahrenheit. There are various medical uses for hypothermia. Therapeutic hypothermia is the only proven effective treatment for post cardiac arrest patients. Hypothermia decreases the amount of cerebral oxygen needed and also lessens the inflammatory response post cardiac arrest. This prevents brain damage and death in patients. There were two major studies done on this topic. One in Europe and one in Australia; they showed very positive outcomes for the patients who were treated with therapeutic hypothermia. More of the patients who received the hypothermic
treatment survived compared to those who did not; also patients treated with hypothermia had less brain damage upon hospital discharge. Sudden cardiac arrest is a major health concern in the United States; there are more than 400,000 incidents annually (AHA, 2011).
Only five to thirty percent of patients survive hospitalization and make it to hospital discharge (AHA, 2011). Doctors are now discovering the highly effective treatment of doctor induced hypothermia for cardiac arrest patients. Hypothermia is defined as a decrease in the core body temperature below 35 degrees Celsius or 95 degrees Fahrenheit (Ward, 2011). It is then characterized by whether it occurred accidentally or if it was induced purposefully. There are multiple uses for medically induced hypothermia. Doctor induced hypothermia is the most effective therapeutic treatment for out-of-hospital sudden cardiac
arrest.
Cardiac arrest patients suffer from ischemic brain injury leading to poor neurologic outcomes and death. Doctors will begin to cool patients as soon as recirculation begins. Therapeutic hypothermia works by decreasing the cerebral oxygen consumption. During cardiac arrest circulation does not occur, therefor the vital organs are not adequately perfused. When resuscitation happens circulation resumes and reperfusion occurs. Reperfusion is associates with free radical formation (AHA, 2011). Mild hypothermia blocks intracellular effects from high calcium concentrations and lessens the inflammatory response after cardiac arrest (Ward, 2011). In 2002 the results of two randomized trials were published that compared mild hypothermia with normothermia in comatose survivors of out-of-hospital cardiac arrest. One study was done in five European countries; the other was conducted in four hospitals in Australia (University of Chicago, 2008). In the European study the patients were cooled to the target range of 32 to 34 degrees Celsius (University of Chicago, 2008). They were kept at that temperature for 24 hours, and then passive warming would begin (University of Chicago, 2008). Six months after cardiac arrest 75 of the 137 hypothermic patients had positive results; and were able to live independently and able to work (University of Chicago, 2008). Whereas with the normothermia patients only 54 of the 137 patients survived six months after their cardiac arrest (University of Chicago, 2008). With the Australian study the patients were cooled to 33 degrees Celsius, kept at that temperature for 18 then active rewarming would begin (University of Chicago, 2008). The results of the Australian study, 21 of the 43 patients treated with hypothermia had good neurological function at discharge compared to nine of 34 patients who were normothermic post cardiac arrest (University of Chicago, 2008). There are various techniques used to cool patients; currently there is not one technique that stands out over the rest in ease of use and high efficiency.
Before the cooling procedure can begin the patient is given a sedative and a neuromuscular blocker to prevent shivering. There are multiple external techniques such as cooling blankets, ice packs, wet towels, and a cooling helmet; however all of these are slow to cool core temperature (University of Chicago, 2008). An intravascular heat exchange device has recently become available; this machine enables rapid cooling and precise temperature control (University of Chicago, 2008). During the whole cooling and rewarming process the patient is closely monitored and their temperature is taken regularly. Not every person who has sudden cardiac arrest is able to receive hypothermic therapy. There are multiple restrictions, and each hospital has its own protocol to follow. Some of the common exclusions are pregnancy, core temperature of less than 30 degrees Celsius post arrest, and known clotting disorders (AHA, 2011). In order to receive hypothermic treatment the patient must be at least 18 years of age, female patients must have a documented negative pregnancy test, cardiac arrest with return of spontaneous circulation, and the blood pressure can be maintained at 90mmHg (AHA,
2011). With the use of therapeutic hypothermia treatment many people have been given a second chance at life. Doctors and scientists are making great strides in refining the technique needed to successfully treat patients with hypothermic therapy.

Ward, J. (2011). Therapeutic hypothermia for victims of cardiopulmonary arrest. AARC Times. 35 (10), 36-46.
American Heart Association. (2011). Therapeutic hypothermia after cardiac arrest. Retrieved April 15, 2011 from http://circ.ahajournals.org/content/108/1/118.full#sec-9
University of Chicago CPR committee. (2008). Therapeutic hypothermia after cardiac arrest. Retrieved April 14, 2011 from http://www.med.upenn.edu/resuscitation/hypothermia/documents/Hypothermia%20Protocol%20Univ%20of%20Chicago%202008.pdf