Continuous chest compressions given by rescue workers during cardiopulmonary resuscitation (CPR) do not improve survival in out-of-hospital cardiac arrest, according to a new study.

The findings do not apply to bystander CPR, where there’s been a growing promotion of the idea that chest compressions are adequate and mouth-to-mouth resuscitation may not be necessary.

When emergency medical services (EMS) workers are trying to revive a patient, there has been concern that even briefly halting compressions might interrupt blood flow and reduce survival.

Using data collected from 114 emergency medical service agencies that treated 23,711 non-trauma cardiac arrests, Graham Nichol, MD, MPH, at the University of Washington in Seattle compared outcomes with continuous versus interrupted compressions.

When EMS personnel were using continuous compressions, “they gave compressions at 100 per minute without pausing, squeezing the bag 10 times per minute. That allows you to give some oxygen and some volume in the lungs, but not as much as when you pause the compressions to get two quick breaths,” Dr. Nichol told Reuters Health.

When interrupted chest compressions were given, the ratio was 30 compressions for every two ventilations. The two ventilations lasted fewer than five seconds, according to the findings, presented at the American Heart Association’s scientific sessions in Orlando and reported online November 9, 2015, in the New England Journal of Medicine.

“Both groups did well, but it appears that the group that did compressions with pauses did a little better,” Dr. Nichol said.

In the group where the chest compressions were continuous, 9.0 percent survived to discharge and 7.0 percent of the total were discharged with favorable neurologic function. With compressions interrupted for ventilation, 9.7 percent survived to discharge, 7.7 percent with favorable neurologic function (p=0.07 for survival; p=0.09 for neurologic function).

In addition, continuous chest compressions produced significantly lower rates of transport to the hospital (p=0.01), lower rates of admission to the hospital (p=0.03) and fewer days of hospital-free survival over 30 days (p=0.004).

“The findings were a surprise to many of the investigators,” Dr. Nichol said. “A lot of us expected that continuous compressions would be better.”

“We don’t have the answer to what the mechanism is. It may be the act of forcing the air into the [lungs] helps with flow. We know that’s the case with animals,” he said.

The National Heart, Lung, and Blood Institute and a number of other organizations supported this research. Sixteen coauthors reported relevant relationships.