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12-09-2011 | Article

CPR duration after EMS arrival does not influence cardiac arrest survival


Free abstract

MedWire News: Extending the duration of initial cardiopulmonary resuscitation (CPR) administered by the emergency medical services (EMS) to patients with out-of-hospital cardiac arrest does not improve their chances of survival, shows a randomized trial from the Resuscitation Outcomes Consortium (ROC).

The ROC Prehospital Resuscitation Impedance Valve and Early Versus Delayed Analysis (PRIMED) study appears in the New England Journal of Medicine. It was a cluster-crossover trial, which compared delivering 30-60 seconds of CPR (during preparation of the defibrillator) with delivering 180 seconds of CPR before rhythm analysis.

The trial was halted early because of a clear lack of benefit with extended CPR. Of the 9933 patients included in the final analysis, 5290 were randomly assigned to early analysis of cardiac rhythm and 4643 to delayed analysis. In all, 5.9% of patients in each group met the primary endpoint of survival to hospital discharge with independent functional status (modified Rankin Scale ≤3).

In a subanalysis, the chances of survival tended to decline with increasing duration of initial CPR among patients with a rhythm amenable to defibrillation who received bystander CPR.

However, Ian Stiell (University of Ottawa, Canada) and colleagues note that the trial did not "address the strategy of immediate analysis of cardiac rhythm without any preceding CPR, since we deliberately insisted on some CPR for the early-analysis group, in the belief that good patient care required cardiopulmonary support while the defibrillator was being prepared."

In a press statement, Stiell said: "While there is some debate about the significance of this result, I think it is better to be on the safe side and stick with the traditional shorter initial CPR approach."

The ROC investigators conducted a second study of use of an impedance threshold device (ITD) concurrently with their study of early versus delayed rhythm analysis, which is published in the same journal. An ITD is "is designed to enhance venous return and cardiac output during CPR by increasing the degree of negative intrathoracic pressure," explain Tom Aufderheide (Medical College of Wisconsin, Milwaukee, USA) and team.

But they found that the 4373 patients assigned to use of the device fared no better than the 4345 assigned to a sham ITD, with 5.8% versus 6.0% meeting the primary endpoint.

Editorialist Arthur Sanders (University of Arizona College of Medicine, Tucson, USA) highlighted the "fundamental tensions between the principles of randomized trial design and the practice of resuscitation that make the conduct of any clinical trial of out-of-hospital cardiac arrest challenging."

For example, he said that in the run-up to the ROC PRIMED study, the ROC achieved an improvement in the chest compression fraction (the proportion of time during which chest compressions are delivered) from 0.66 to 0.71, on average, across the study sites.

Most emergency services will not have such good compression fractions, said Sanders, and it is not clear how the duration of initial CPR would affect patient outcomes in such services.

The drive to improve chest compression fractions occurred after a database analysis showed that larger fractions were linked to better chances of survival. "Ironically, this analysis and the resulting improvements in process may have greater importance for clinical practice" than the two randomized trials," said Sanders.

By Eleanor McDermid