"I think the evidence is still out, but it makes sense to say that feedback helps improve performance" of CPR, says Carolyn L. Cason, interim vice president for research at the University of Texas at Arlington.

How Much Does Feedback Help?

Its effectiveness at improving CPR depends on the type of feedback that is given, the nature of that feedback, and when and how it is given, says researcher Carolyn L. Cason.

A recently published Danish study concluded that receiving verbal and visual feedback about cardiopulmonary resuscitation performance did not affect the quality of CPR done during a two-minute period by a group of trained rescuers. The study, published online Feb. 28, 2012, in the Scandinavian Journal of Trauma, Resuscitation and Emergency Medicine, attempted to investigate the impact of feedback on quality of chest compressions with the hypothesis that feedback delays the deterioration of compression quality over time.

Several studies have investigated whether and to what extent feedback in various forms can optimize CPR, which is an important question because evidence shows the quality of chest compressions falls off quickly. A 2009 study published in Resuscitation indicated compression depth during actual in-hospital CPR decayed after 90 seconds, although caregivers' rate of compressions did not change. More than a decade ago, in 2000, a study in which 24 paramedic students with previous BLS training participated found that audio feedback from a manikin immediately improved the depth and duration of their chest compressions, marking feedback as an important training tool.

Four researchers from the College of Nursing and the Department of Kinesiology at the University of Texas at Arlington (UTA) recently examined visual feedback, auditory feedback, and no feedback on CPR performance by trained rescuers who performed the 30:2 ratio -- rather than hands-only CPR -- for 10 minutes. They found visual feedback worked best, but that’s not the whole story, said Carolyn L. Cason, interim vice president for research at UTA and leader on this study (available at http://www.biomedcentral.com/1472-6955/10/15).

"The visual feedback was continuous. The auditory feedback lagged," she said. "It's a perfect compounding between mode of feedback and the type of feedback. The visual feedback was continuous, so was the visual feedback better? Or was it continuous versus lag? We cannot say that visual was better because it is perfectly compounded with continuous."

She said the effectiveness of feedback depends on the type of feedback that is given, the nature of that feedback, and also when and how it is given.

"I think the evidence is still out, but it makes sense to say that feedback helps improve performance," said Cason. "Whether or not it helps to improve performance in CPR is a function of what the nature of that feedback is. You know, with CPR training, for years we used to use a metronome to help individuals get the rhythm. I think everyone thought that that worked quite well because you get the beat and, in more recent years, various training operations have tried to use tunes. [You were] singing the song as you were delivering compressions because it had the same rhythm that would set you up for the appropriate rate of compressions."

The point of the metronome was getting the pattern -- the compression rate -- right. "Rate is one of the things that most people can more or less get, so rate has not been that much of a problem until you change the nature of the feedback," said Cason. "In our study, the feedback was lagged so that the manikin and the programming was detecting over time that you were not compressing fast enough. So the verbal feedback was 'press faster.' That's why you saw the unevenness in the patterns. I'm compressing and, with time, I'm losing the rhythm, if you will, so my rate is going down. I get feedback so I'm starting to go again. That's why you see that variation, and it has to do with the nature of the feedback.

"It's delayed feedback, and what I think you need is real time, like with the metronome or some other system that might be used. So that's with respect to rate. With respect to depth, that's been a challenge, I think, for a while, and we're just beginning to get a handle on it. It's a harder one to learn. The more advanced training manikins provide feedback on that, but again, it's verbal feedback like 'press harder.' Again, there's the problem of the built-in system not working very effectively."

Cason compared the process of optimizing CPR with training elite athletes, noting her colleagues on the study are working in athletic training, kinesiology, and exercise physiology. "I don't know if you're a big sports fan or not, but the way in which we groom batters, basketball players, and football players is a fairly extensive feedback system, not only on what they're doing but how to correct it," she said. "The same holds true for CPR."

Some automated external defibrillators provide valuable audible and visual feedback to the rescuer. Asked about mechanical CPR devices, she said, "I know that there is some evidence to suggest that they are effective. Of course, I think you would only see them in a hospital situation, but you've still got [to take] time for setup and all of that, so you've still got some immediate resuscitation you have to be engaged in.

"And if you look at it, it's that immediate response that's really important to survival," she added. "My experience with those devices is that they're fairly cumbersome. Much of the literature that I've looked at comes from the people who develop them. They meet the criteria of what the American Heart Association says should be happening in terms of rate, depth, release, etc., because it's all controlled by the machine itself."

Findings About Rescuers' Fatigue
The basic thrust of the UTA group's paper is that giving continuous feedback seemed to work better than giving intermediate feedback because the lag in intermediate feedback allows rescuers' performance to decay. The most difficult part of CPR to perform optimally is complete release of the chest at the end of every compression, but it, too, is amenable to feedback, she said.

Cason and her colleagues concluded rescuers' fatigue is not the cause of the decay in the quality of performed CPR. Some investigators continue to insist that fatigue is at work, "but if you look at what the actual body says in terms of actual fatigue, it's not fatigue. If you put that together with what we're beginning to see about feedback, you lose your way because you're not getting feedback that you need to modify your performance. If you get feedback, you should be able to maintain your performance," she explained. "I would anticipate that if you were actually doing CPR for long enough, it would eventually begin to decline due to fatigue. Just think about what happens to the body in terms of the waste products that are built up. Eventually, yes, but not within the two minutes [cited by some studies]."

Today, feedback is available to bystander responders through calling 911 or even by using 911 apps. "I'm not real sure what the nature of the feedback is," Cason said. "The 911 operators, their first thing is to give the person who is on the phone just some general instructions about where to place the hands. Mostly what I think they're saying is 'Press hard and press deep.' Whether or not they're giving any sort of rhythmic information, I don't know. That would be the simplest to do over the phone. You establish the beat and you say that is a constant in the background, and they try to keep up with that. That would seem the most reasonable kind of a thing."

The UTA study was a laboratory study involving 15 female volunteers who used training manikins. Cason and her colleagues have finished another study they hope to publish soon. Presented as a poster at an American Heart Association conference last year, this study evaluated the quality of CPR when it is performed on different mattress surfaces. CPR performed in hospitals is very different from how EMS professionals and lay people are trained, with the manikin lying on the floor.

"In the hospital, we don't put the person on the floor to deliver CPR. So the different surfaces and the backboards and various things of that nature are being evaluated," Cason said. "The most recent study that we did, we put the backboard on two different mattresses. One of them is a mattress that comes on a bed that, when there is an event for which you need it to firm, it firms. It mitigates the loss of force, because if you've got someone performing chest compressions on someone who's in the bed, you have give because the bed gives.

"What we found was you mitigate loss of force if you have the backboard on one of these inflating mattresses. The challenge here is getting a firm enough surface so that you're not losing that force."

This article originally appeared in the May 2012 issue of Occupational Health & Safety.

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