Studies conflict on automated CPR benefits

14 June 2006

Two articles published in this week's Journal of the American Medical Association offer contradictory results on the benefits of device-assisted versus manual cardiopulmonary resuscitation (CPR) in patients with out-of-hospital cardiac arrest.

One study found similar short-term survival with the two systems, but worse neurological outcomes when using the load-distributing band (LDB) automated compression device, which provides circumferential chest compression using an electrically activated constricting band on a short backboard.

The second study reported that survival improved with the LDB device compared with conventional manual CPR, with similar neurological outcomes.

Automated mechanical chest compression devices were developed in order to offer optimal chest compressions during CPR, as maintaining consistent manual compressions can be difficult.

In the first study, Al Hallstrom (University of Washington, Seattle, USA) and co-workers randomly assigned 554 patients to a LDB device approved by the US Food and Drug Administration, and 517 to manual CPR in a multicenter, cluster-randomized trial in five communities.

The study was terminated early, on the recommendations of the independent safety monitoring board, after interim findings showed a lack of benefit in the primary outcome of survival to 4 hours and apparent harm in secondary outcomes.

Results showed that survival to 4 hours was similar with manual and LDB CPR, both overall (29.5% vs 28.5%) and in the primary comparison population of 767 patients in cardiac arrest at the time of arrival of the emergency medical services (EMS) whose arrest was considered of cardiac origin.

But, in the primary population, survival to hospital discharge was higher with manual than device CPR (9.9% vs 5.8%), a result that had borderline statistical significance (p=0.06, adjusting for covariates and clustering).

Neurological outcome was also better with manual CPR than with the LDB, identified as a cerebral performance category of 1 or 2 (7.5% vs 3.1%, p=0.006).

The researchers conclude: "Device design and implementation strategies may need further preclinical evaluation."

In the second, retrospective study, Marcus Ong (Virginia Commonwealth University, Richmond) and co-workers compared outcomes before (n=499) and after (n=284) incorporation of the same LDB device at a single EMS system.

The team found that manual CPR offered worse results than the LDB in terms of the primary outcome of return of spontaneous circulation (20.2% vs 34.5%), and also the secondary outcomes of survival to hospital admission (11.1% vs 20.9%), and survival to hospital discharge (2.9% vs 9.7%).

"The number needed to treat for the adjusted outcome survival to discharge was 15," the authors say, adding that the LDB did not affect neurological outcomes.

Roger Lewis (Harbor-University of California Los Angeles Medical Center, Torrance) and James Niemann (University of California) questioned in an accompanying editorial whether the differing conclusions could be reconciled.

They said: "The best current information suggests that the degree of benefit or harm associated with use of the LDB-CPR device is influenced by the details of its use - perhaps including selection of the patient population with respect to presenting rhythm, time from cardiac arrest to initiation of CPR, and almost certainly time-to-deployment and the influence of deployment on time-to-defibrillation, when appropriate."

JAMA 2006; 295: 2620-2628, 2629-2637