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Tuesday, January 14, 2014

Why Neurointensivists Are Rethinking the Prehospital Hypothermia Protocol After Cardiac Arrest



Contrary to expectation, prehospital cooling does not improve neurologic outcomes or survival after cardiac arrest, and increases the risk of re-arrest and pulmonary edema, according to a study published in the Jan. 1 issue of the Journal of the American Medical Association (JAMA). These results, combined with another recent study that found cooling to 33o C no better than cooling to 36o C, “question the entire practice as to whether hypothermia is beneficial in cardiac arrest,” according to one expert not involved in the trial, or instead whether simply avoiding fever should be the major goal.

The JAMA study, led by Francis Kim, MD, associate professor of medicine at the University of Washington and Harborview Medical Center in Seattle, could hardly have been more definitive. Over a five-year period, Dr. Kim randomized 1359 patients with cardiac arrest to either standard care or prehospital cooling with up to 2 liters of 4o C intravenous normal saline, begun by emergency responders on the way to the hospital, as soon as spontaneous circulation returned. This represented about 40 percent of all patients with cardiac arrest in the Seattle area during that time; the remainder could not be resuscitated.

On average, patients were cooled by about 1.2o C by the time of their arrival at the hospital, usually within half an hour after arrest, and the intervention reduced the time to achieve target cooling of 34o C by about an hour. However, it had no effect on the rate of survival to hospital discharge or on neurologic outcome among surviving patients, either among patients with ventricular fibrillation (VF) or non-VF arrest.

“Obviously, this was disappointing to us,” Dr. Kim said, since it had been widely assumed that the earlier cooling could be started, the better. Many centers across the country have instituted field cooling for cardiac arrest patients, he said, based on that assumption. But Dr. Kim’s results echo those from a smaller trial published in the journal Circulation in 2010, which indicated no benefit from prehospital cooling with Ringer’s solution.

However, the results from Dr. Kim’s trial were not simply that field cooling offered no advantage to patients. Instead, those patients randomized to prehospital cooling experienced re-arrest on the way to the hospital more often — 26 percent versus 21 percent — as well as increased pulmonary edema and use of diuretics. The reasons for this increased morbidity are not clear, but animal models suggest that intravenous cooling may be linked to decreased coronary artery perfusion pressure, compared with surface cooling. Blood gas pH and partial pressure of oxygen are also reduced, potentially worsening outcomes.

“The results of this randomized study,” in conjunction with the 2010 study, “do not support the routine use of cold saline following return of spontaneous resuscitation among patients resuscitated from prehospital cardiac arrest,” Dr. Kim concluded.

See the full discussion by outside experts on what this study may mean for the future of neurointensive care in our Jan. 16 issue of Neurology Today. Browse our archives for previous coverage of the hypothermia protocol for cardiac arrest: