In adults with out-of-hospital cardiac arrest, prehospital cooling decreased the mean core temperature in patients with and without ventricular fibrillation (VF), and reduced the time to achieve a temperature of less than 34°C, but did not improve the primary outcomes of survival or neurological status at discharge, according to results of the Induction of Mild Hypothermia Following Out-of-Hospital Cardiac Arrest trialpresented Nov. 17 as part of AHA 2013, and published simultaneously in the Journal of the American Medical Association.

The trial randomized 1,359 adults "with prehospital cardiac arrest to standard care with or without prehospital cooling, accomplished by infusing up to 2 L of 4°C normal saline as soon as possible following return of spontaneous circulation." Results showed "survival to hospital discharge was similar among the intervention and control groups among patients with VF (62.7 percent [95 percent CI, 57.0 percent - 68.0 percent] vs. 64.3 percent [95 percent CI, 58.6 percent -69.5 percent], respectively; P = .69) and among patients without VF (19.2 percent [95 percent CI, 15.6 percent - 23.4 percent] vs. 16.3 percent [95 percent CI, 12.9 percent - 20.4 percent], respectively; P = .30)."

Further, "the intervention was also not associated with improved neurological status of full recovery or mild impairment at discharge for either patients with VF (57.5 percent [95 percent CI, 51.8 percent - 63.1 percent] of cases had full recovery or mild impairment vs. 61.9 percent [95 percent CI, 56.2 percent - 67.2 percent] of controls; P = .69) or those without VF (14.4 percent [95 percent CI, 11.3 percent - 18.2 percent] of cases vs. 13.4 percent [95 percent CI, 10.4 percent -17.2 percent] of controls; P = .30)."

The authors add that "the intervention decreased mean core temperature by 1.20°C (95 percent CI, -1.33°C to -1.07°C) in patients with VF and by 1.30°C (95 percent CI, -1.40°C to -1.20°C) in patients without VF by hospital arrival and reduced the time to achieve a temperature of less than 34°C by about 1 hour compared with the control group."

"Under the conditions of our study, early cooling in the field didn't improve neurologic outcomes or survival following resuscitation from out-of-hospital cardiac arrest," said Francis Kim, MD, FACC, lead author of the study and an associate professor of medicine in the cardiology division of the University of Washington in Seattle.

The authors conclude that "although hypothermia is a promising strategy to improve resuscitation and brain recovery following cardiac arrest, the results of the current study do not support routine use of cold intravenous fluid in the prehospital setting to improve clinical outcomes."

An editorial comment by Christopher B. Granger, MD, FACC, of the Duke Clinical Research Institute, Durham, North Carolina, and Lance B. Becker, MD, of the Center for Resuscitation Science, University of Pennsylvania Health System, Philadelphia, notes that based on the study results, "emergency medical servicesagencies should concentrate on other means to improve survival from cardiac arrest. These include optimizing dispatch processes, ensuring quality cardiopulmonary resuscitation, transporting of patients to hospitals capable of providing quality cardiac arrest care, and measuring and continuously improving quality measures of cardiac arrest care."

They caution that the study results "should not be extended to use of other methods of hypothermia initiated in the emergency department or continued during the initial phase of postresuscitation care in the intensive care unit." They add that moving forward, "more trials are needed to answer vital questions regarding the use of hypothermia."

Keywords: Resuscitation, Out-of-Hospital Cardiac Arrest, Hypothermia, Cardiopulmonary Resuscitation, Ventricular Fibrillation, Heart Arrest, Patient Discharge, Cold Temperature