Healthcare professionals often administer therapeutic hypothermia to optimize survival of both out-of-hospital and in-hospital cardiac arrest. While there are several studies that support therapeutic hypothermia after out-of-hospital cardiac arrest (OHCA), there had been no studies investigating its use for in-hospital cardiac arrest (IHCA) and a paucity of data of its comparative effectiveness — until now.

There are more than 350,000 out-of-hospital cardiac arrests in the United States each year, according to the American Heart Association, and the overall survival rate for OHCA is 12 percent. About 209,000 people have IHCAs in the U.S. each year, and about 24.8 percent of adults who suffer in-hospital cardiac arrest survive.

The American Heart Association guidelines on therapeutic hypothermia suggest therapeutic hypothermia, which consists of cooling the bodies of unconscious patients to 32-34 degrees C for 12-24 hours, after IHCA. Cooling the body for 24 hours then slowly rewarming limits the effects of cerebral hypoxia and reperfusion, slows cerebral metabolism, limits cerebral cell death and lessens cerebral edema.

The objective of the study entitled "Association Between Therapeutic Hypothermia and Survival After In-Hospital Cardiac Arrest" and published this month in the Journal of the American Medical Association (JAMA) was to evaluate the association between therapeutic and survival after IHCA.

For this cohort study, researchers used information from the Get With the Guidelines-Resuscitation registry. The scientists collected information about 26,183 patients successfully resuscitated after IHCA between March 1, 2002, and Dec. 31, 2014, with follow-up ending Feb. 4, 2015. The researchers included both patients treated and not treated with hypothermia at 355 hospitals in the United States.

The researchers set survival to hospital discharge as the primary outcome of the study. They also included favorable neurological survival, as defined as a Cerebral Performance Category score of one or two, as a secondary outcome.

The investigators used a matched propensity score analysis to compare and examine data for all cardiac arrests combined. They also performed separate analysis and examination shockable cardiac arrests, such as ventricular fibrillation and pulseless ventricular tachycardia, and for nonshockable asystole and pulseless electrical activity.

Of the 26,183 patients with IHCA, doctors treated 1,568 with therapeutic hypothermia. The researchers matched 1,524 of these patients by propensity score to 3,714 patients who did not receive therapeutic hypothermia.

The mean age of those who received therapeutic hypothermia was 61.6 years, while the mean age of those who did not was 62.2 years. Just over 58 percent of the patients who received therapeutic hypothermia were male; 57.1 percent of those who did not receive therapeutic hypothermia were male.

After adjustment, therapeutic hypothermia was associated with a lower in-house survival rate, at 27.4 percent versus 29.2 percent. The researchers found a similar association for those who suffered nonshockable cardiac arrest rhythms, at 22.2 percent versus 24.5 percent.

In the overall cohort, those who receive therapeutic hypothermia also had lower rates of favorable neurological survival, at 17 percent of those receiving therapeutic hypothermia having favorable neurological survival compared with 20.5 percent of those who received usual care.

The researchers matched patients to their Medicare information, which allowed the scientists to follow up and compare 706 patients treated with hypothermia to 2,035 controls for one-year survival. The scientists found that survival rates were similar between both groups.

This new study suggests the use of therapeutic hypothermia may actually lower likelihood to hospital discharge and decrease the chances of a favorable neurological survival among patients suffering an in-hospital cardiac arrest. Randomized clinical trials are needed to assess efficacy of administering therapeutic hypothermia after IHCA.