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Outcomes of Hypothermia After Cardiac Arrest
Abstract & Commentary
By Michael H. Crawford, MD
Source: Dumas F, et al. Hypothermia after cardiac arrest effective in both shockable and nonshockable patients? Circulation 2011;123:877-886.
Current guidelines recommend hypothermia for comatose survivors of out-of-hospital cardiac arrest in whom return of circulation has been achieved. This observational study from Paris, France, evaluates the outcomes of hypothermia in such patients comparing those whose presenting rhythm was ventricular tachycardia (VT) or fibrillation (VF) to those with pulseless electrical activity (PEA) or asystole. Hypothermia to a body temperature between 32° and 34° degrees Celsius was done for 24 hours, then passive re-warming was allowed. Over 9 years, 1145 non-traumatic out of hospital cardiac arrest patients were successfully resuscitated in the field and admitted to their ICU. VT/VF was the initial rhythm in 708 (62%) and PEA/asystole in 437 (38%). About two-thirds of each group were treated with hypothermia. A good neurological outcome was more common in those with VT/VF who were cooled (44%) compared to those not cooled (29%) and those with PEA/asystole (15% cooled, 17% not). The odds ratio for a good outcome with cooling in VT/VF patients was 1.9 (95% confidence interval [CI], 1.18 to 3.06) whereas in PEA/asystole patients it was 0.71 (95% CI, 0.37 to 1.36). The authors concluded that in a large group of successfully resuscitated but comatose out of hospital cardiac arrest cases, hypothermia is associated with better neurological outcomes in patients presenting with VT/VF as compared to PEA/asystole.
This observational study provides insight into the expected results of hypothermia treatment for comatose survivors of out of hospital cardiac arrest. The main conclusion is that patients whose initial rhythm was VT/VF vs PEA/asystole have better outcomes with hypothermia. What is not clear is why. The authors point out that patients with PEA/asystole should not be denied hypothermia based upon their study, since it was not a randomized trial. Also, the hypothermia protocol may need to be different for these patients. In addition, the fact that in the VT/VF group hypothermia patients had better outcomes than those not given hypothermia should not be a blanket prescription for hypothermia in all such patients. There were undoubtedly selection biases between who did and did not get hypothermia in this group. Current guidelines for initiating hypothermia should be followed for all cardiac arrest patients.
The main strengths of this study were the large number of patients and the outstanding urban emergency medical system in Paris. The authors point out that over the 9 years of the study, the use of hypothermia increased. It would have been informative to know more about the decision-making criteria for using hypothermia in these patients. Since the proportion of patients with VT/VF and PEA/asystole who got cooling was about the same, there is probably little bias in the main conclusion of this study.