Therapeutic hypothermia significantly raises the rate of survival with a good neurologic outcome among patients who are comatose after a cardiac arrest with a nonshockable initial rhythm, according to a report published online November 16 in Circulation.
Many observational and retrospective cohort studies have examined the possible benefits of therapeutic hypothermia in this patient population, but they have produced conflicting results. No prospective randomized clinical trials have been published as yet. This has led to controversy. Some clinicians insist the treatment should be reserved only for patients who meet the narrow criteria for which there is good supportive evidence; others, eager for any clinical strategy that can improve the outcomes of these critically ill patients, routinely expand its use to comatose patients regardless of their initial heart rhythm or the location of the cardiac arrest, wrote Dr. Sarah M. Perman of the department of emergency medicine, University of Colorado, Aurora, and her associates.
They studied the issue using data from a national registry of patients treated at 16 medical centers that sometimes use therapeutic hypothermia after cardiac arrest. They assessed the records of 519 adults during a 3-year period who had a nontraumatic cardiac arrest and initially registered either pulseless electrical activity or asystole, then had a return of spontaneous circulation but remained comatose. Approximately half of these comatose survivors (262 patients) were treated with therapeutic hypothermia according to their hospital’s usual protocols, and the other half (257 control subjects) received standard care without therapeutic hypothermia.
Patients who received the intervention were significantly younger (62 vs 69 years), had a longer duration of cardiac arrest (23 vs 13 minutes), had a higher incidence of asystole as their primary cardiac rhythm (45% vs 35%), and were much more likely to have a an out-of-hospital cardiac arrest (82% vs 39%). To account for these marked differences and to control for confounding by indication, the investigators used propensity matching and identified 200 matched pairs of patients.
In the propensity-matched cohort, the rate of survival to hospital discharge was significantly higher with therapeutic hypothermia (29%) than without it (15%), as was the rate of survival with a favorable neurologic outcome (21% vs 10%). And in a multivariate analysis of factors contributing to positive patient outcomes, the intervention was associated with a 3.5-fold increase in favorable neurologic outcomes. A further analysis of the data showed that therapeutic hypothermia was associated with improved survival, with an OR of 2.8, the investigators said.
In addition, an analysis of outcomes across various subgroups of patients showed that regardless of the location of their cardiac arrest, patients were consistently more likely to survive to hospital discharge neurologically intact if they received therapeutic hypothermia (OR, 2.1 for out-of-hospital and OR, 4.2 for in-hospital cardiac arrest).
“These results lend support to a broadening of indications for therapeutic hypothermia in comatose post-arrest patients with initial nonshockable rhythms,” Dr. Perman and her associates said.