Hypothermia for Neuroprotection in Adults After Cardiopulmonary Resuscitation
Arrich J, Holzer M, Herkner H, Müllner M
Cochrane Database Syst Rev. 2009;CD004128
Study Summary
Cardiac arrest is a devastating clinical event. Its cause may be less important than the process and outcomes of resuscitation, given the often dismal neurologic recovery and overall survival after arrest. Following the publication of 2 seminal articles in 2002, interest in hypothermia as a rescue strategy to improve neurologic outcomes after cardiac arrest has grown. The Cochrane Collaboration, known for its systematic reviews, sought to determine whether the cumulative evidence on hypothermia supports its use as a standard of care after cardiac arrest.
Arrich and colleagues searched the Cochrane Central Register of Controlled Trials, Medline, EMBASE, CINAHL, PASCAL, and BIOSIS for clinical reports of randomized, controlled trials assessing therapeutic hypothermia in adult patients that was initiated within 6 hours after cardiac arrest. Four trials and 1 abstract that reported on 481 patients were included in the systematic review. With conventional cooling methods, patients in hypothermia groups were more likely to reach a cerebral performance score at the best or next-best level (1 to 2 on a scale of 5) during their hospital stay and were more likely to survive to hospital discharge than were patients who received standard postresuscitation care. Across all studies, no significant differences in adverse events were noted between hypothermia and control. The investigators concluded that conventional cooling methods to induce mild therapeutic hypothermia seem to improve survival and neurologic outcome after cardiac arrest.
Viewpoint
A growing number of hospitals are putting protocols in place to initiate hypothermia in patients who have had cardiac arrests, although at present, we don't know how widespread these protocols are in terms of development and application. The study recommends the use of hypothermia after cardiac arrest, especially in the first 6 hours. However, the clinical trials from which this recommendation is made had additional criteria that may be important at certain institutions and particularly for individual patients. Hypothermia has been applied in patients with abnormal neurologic function at baseline (not completely normal or a depressed Glasgow coma score after resuscitation, not the result of other causes). Most studies have included only patients with out-of-hospital cardiac arrest with initial cardiac rhythms showing ventricular fibrillation or nonperfusing ventricular tachycardia. Furthermore, studies have excluded patients with prolonged periods (> 15 minutes) from the time of arrest to first medical attempts at resuscitation, a cardiopulmonary resuscitation period of more than 60 minutes before return of spontaneous circulation, or shock after resuscitation.
Given these limitations, the application of moderate hypothermia (32°C to 34°C core temperature) within the first 6 hours after cardiac arrest and sustained over a 24-hour period is consistently associated with improved neurologic outcomes and overall survival. Whether these results can be extrapolated to in-hospital arrest or non-ventricular tachycardia or non-ventricular fibrillation arrests remains to be seen. In the meantime, the next big question is how to implement a system to initiate hypothermia in patients who have cardiac arrest not just in hospitals, but in communities at large, with integration of emergency medical services and receiving hospitals to optimize outcomes.
Abstract