Cardiac & Resuscitation

The Importance of Count and Cadence of Chest Compressions

As you’ll read in multiple other sections of this supplement, we continue to discern insights into more effective treatment approaches to out-of-hospital sudden cardiac arrest. In reality, we’ve collectively learned more in just the last decade than ever before about the pathophysiology of cardiac arrest.

With considerations about cooling (therapeutic hypothermia), chest compression continuity and alternative ventilation strategies, is there really much to talk about when it comes to something as simple as the rate of chest compressions?

“So, Dr. G, what’s your interest in chest compression rate? The American Heart Association (AHA) says to compress the cardiac arrest victim’s chest at least 100 times a minute. That’s all there is to it, right?”

That’s a good place to start and an understandable question. For purposes of this particular conversation, let’s discuss victims who are of adult age. You’re correct in your interpretation of the AHA guidelines released in late 2010.1 How the 2015 guidelines on chest compression rate will change, if at all, is unknown.

There’s been some interesting science published regarding chest compression rates since those 2010 guidelines.2,3 I’m quite sure the clinicians and scientists charged with formulating those 2015 guidelines will certainly take such discoveries into account. The fact is—no surprise here, I think—nothing is very simple when it comes to a condition as dynamic, dramatic and challenging as cardiac arrest.

Key among the latest scientific papers on chest compression rate is work done by Dr. Ahamed Idris and his colleagues in the Resuscitation Outcomes Consortium. In short, Dr. Idris and the research team found that exactly 100 chest compressions per minute didn’t produce the highest number of survivors among the large group of cardiac arrest victims who were treated by systems that participate in the ROC.4

The “sweet spot” of chest compression rate in that review, published in 2012, was much nearer to 120 chest compressions per minute.4 So, you might say that the AHA is still right because 120 compressions per minute fits the definition of “at least 100 times a minute,” although so does 140 compressions per minute, correct?

“The patients (and their families) we treat often think more is better, and if we want to be honest, many EMTs and paramedics subscribe to that belief about a lot of interventions. That said, I bet you’re getting ready to burst that bubble and tell us 140 compressions per minute may not be better?”

Actually, I’m not going to say 140 compressions per minute may not be better than a rate of 120. Instead, I’m going to say, based upon the Idris paper, that 140 compressions per minute are definitely not better for survival than 120. In that report, a very compelling graph is presented that I choose to describe as a “wave of survival per compression rates.”

The reason I call it a “wave” is that a curve implies an even rise and fall and this isn’t that. The scientific term for the actual curvilinear shape is a cubic spline model, but that’s hard for a guy like me to immediately grasp. I can visualize a wave that rises and then fades out, and I think most people can as well.

So back to that study, it’s not too hard to imagine that survival proved lower at rates less than 100 compressions per minute and then there is a slow increase to a peak in survival near 120 compressions per minute.

Here’s my key point: After 125 and towards 140 and beyond, the survival line drops off! That’s why this study is so important in my opinion, and I trust the researchers, their method of study, plus the number of patients involved was large. This is science you and I can use in our quest to produce more neurologically intact survivors from out of hospital sudden cardiac arrest.

“Why do you think 140 isn’t better than 120? Besides, are people in real life compressing at 140 anyway? That seems pretty fast and not what’s taught in the first place.”

Let me break that up into two answers. First, we have to think about this amazing organism that is the human body. What happens when you and I decide we’re going to get our particular organisms in better shape and do some aerobic conditioning or weightlifting? Why does our heart rate rise and breathing increase? We are doing the “Magic C” as I call it—compensating!

That workout-induced tachycardia and tachypnea is getting greater-than-usual oxygen-enriched blood flow to muscles that require it to perform what we’re asking of them. As long as we are pulsatile, and your patient is pulsatile, our human bodies will stretch compensation to impressive levels. But, what happens when pulsatile becomes pulseless? Compensation ceases, at least the intrinsic compensation.

So what’s the extrinsic compensation during CPR? You. Me. Your partner(s). Bystander(s). CPR is, in one word, compensation.

What percent of compensation do you and I have to attain for a person when we do CPR? 100%! Sobering, huh? We don’t even get to outsource 1%; that 100% needs to be the very best it can be, at least according to the best understanding of what works today.

As important as each compression is, the decompression phase is just as important because that’s when intrathoracic pressure drops and blood flow can return to the heart to be available for flow from the heart on the next compression. Think about the last sick patient you had in a true tachydysrhythmia with a pulse? Why were they so weak, hypotensive and likely even hypoxic? The rapidity of their pulse prevented good cardiac output and perfusion, both to central and peripheral circulation.

We may not be so worried about peripheral perfusion in cardiac arrest, but if our compressions are going to produce helpful cerebral and coronary perfusion pressures, we have to let enough decompression time occur. That doesn’t happen if we compress at 140 times a minute.

Metronomes attached to monitor/defibrilators allow agencies to fine tune CPR compression rates

Metronomes attached to monitor/defibrilators allow agencies to fine tune CPR compression rates

Metronomes attached to monitor/defibrilators allow agencies to fine tune CPR compression rates to keep up with the latest scientific evidence. Photos David Howerton

So do professionally trained EMTs and paramedics compress that fast anyway? Actually, yes, a lot do. Good-hearted, enthusiastic police officers, firefighters, EMTs and paramedics perform too many compressions. How do I know this? Back in 2011, we discovered in the process of reviewing chest compression fundamentals with each and every EMT and paramedic in the EMS System for Metropolitan Oklahoma City and Tulsa, that without a metronome to guide compressions, nearly 90% of these incredibly well-trained men and women were compressing somewhere between 135–145 times per minute!

That really opened my eyes. It affirmed to me several things: 1) We have EMS professionals in our system who really care about—and work hard at—treating cardiac arrest. Even in training scenarios, their adrenaline kicks in and they go after it! I had honestly thought if we did start using metronomes set at 120 beeps per minute, directly influenced by that ROC study we’ve been talking about, those metronomes would be needed to speed up the rates. But, I was wrong. The reverse was true; we were compressing too fast and the metronomes would help us to slow down.

It became crystal clear to me we needed to begin using metronomes to change natural compression rate tendencies. This turned out to not just be a positive for the patients, but our crews also, because we were actually able to reduce the physical work necessary in performing optimal manual chest compressions.

“Cool, Dr. G. So just compress at 120 a minute in adults, use metronomes set to that and that’s all there is to it?”

Even with what we’ve discussed so far, there’s more to it. To prove the point, I’ll share with you now that we recently changed our compression rate guideline, and metronomes, to 110 compressions per minute in rate.

“What?!?! How does that make sense based upon what we’ve been talking about?”

Back to the “nothing is really simple when it comes to cardiac arrest” mindset. In our particular system, we currently don’t use mechanical chest compression devices like the Physio-Control LUCAS 2 chest compression system or ZOLL AutoPulse non-invasive cardiac support pump. We use a team dynamic plan for coordinated resuscitation (aka the “pit crew” approach). The most common resuscitation in metro Oklahoma City or Tulsa has 5–8 EMS professionals on scene within 4–10 minutes.

In addition, one of the devices we choose to use in our airway management and cardiac arrest care is the ResQPOD impedance threshold device (ITD) for its capability of reducing intrathoracic pressure during decompression—another important factor in cardiac arrest resuscitation.5

Further, because of the emphasis we’ve been placing on the continuity of chest compressions and getting quick feedback to our colleagues about how consistent in rates and continuity that their compressions were or were not in individual resuscitations, we’ve seen our chest compression fraction (time of resuscitation in which chest compressions are occurring) move from a typical 85% to more than 95%.

Without getting too far down in the weeds of science, it’s important to point out that use of mechanical chest compressors and/or the impedance threshold device can influence the basic physiology of hemodynamics produced by compressions.

Through very in-depth conversations that I’ve had over the past few years with the clinical scientists who developed the impedance threshold device, it appears that the ideal compression rate for CPR without an ITD, as reported in the Idris paper, differs from what’s ideal if an impedance threshold device is used in-line in the airway circuit.

It seems the best rate when using an impedance threshold device is much closer to the 100 compression rate per minute; in fact, in subsequent data analysis, the best overall survival in the ROC study occurred in patients who received an active ITD with chest compression rates close to 100/min. So, we’re slowing down to 110 for now, primarily based upon both this specific data analysis and our system-specific chest compression fraction and effective compressions per minute. We’ll continue to follow our survival outcomes and adjust our chest compressions rates as further observation and science dictates.

To illustrate how complex this can get, if active compression-decompression CPR with an ITD finds its way to the streets of the United States, that ideal chest compression rate may be as low as 80/min according to a recent U.S. study!6

It does make sense when you appreciate that all of these things produce different compression types and intrathoracic pressure and, thus, different compression types and adjuncts, like the ResQPOD ITD and mechanical compression devices, will produce different optimal rates.

Just remember, it still is all about survival and there are a lot of “fine tuning” knobs to turn back and forth as science gives us updates to our user’s manual for resuscitation.

“Wait, Dr. G. So you’re talking a lot about rate, but not so much specifically about metronomes. Seems like those are more important than you first thought and if anything, they’re getting even more important. Why don’t the monitor/defibrillators have metronomes adjustable from 100 per minute? Should we ignore those? And, what metronomes should we be buying?”

First, you’re right. Metronomes are far more important than I first thought. In fact, credit goes to paramedics in our system who pushed the concept. I’ll claim to be smart—smart enough to listen to what proved to be their great idea.7

Those early metronomes came about because not all the responding companies (fire-based) had manual monitor/defibrillators and not all of our monitor/defibrillators had built-in metronomes at the time. And, for my manufacturing colleagues reading this article, I’ll admit some frustration at the lack of their built-in metronomes being changeable in rate. But, I’ll also admit that I understand the frustration that these manufacturers have themselves because they can’t put a “dial the rate up or down” knob or touchscreen on their devices without a time-intensive and costly journey through the Food and Drug Administration review and approval process.

Should you ignore those metronomes that come with the cardiac monitor/defibrillators? Not if your local medical oversight physician(s) want you to use them. If they do, please use them per your system-specific treatment guidelines.

In our system, we’ve purchased musical metronomes that do allow for rate changes. This made it possible to start at 120 beeps per minute, change to our current 110 beeps per minute, and still allow for future changes. I’m pretty sure these music industry companies have no idea what paramedics are doing ordering dozens of metronomes. They probably think we’ve got some great garage bands in urban Oklahoma!

Many options exist in the marketplace. I recommend you try to find something that’s easy to activate and see or hear, with the durability of the proverbial EMS steel ball, something that allows for rate changes (but doesn’t allow crews to change it to undesired rates or allow unintended changes in rates), and something sized to promote ready accessibility.

There are a lot of smartphone apps with audible and visual metronomes that are adjustable as well. We considered use of smartphone apps, but didn’t want to ask our EMS professionals to use their personally owned devices in the provision of resuscitation.

Many of the agencies in our EMS system have found great ways to physically attach  metronomes to the outside of their AEDs or manual monitor/defibrillators so initial arrival EMTs and paramedics don’t have to go fishing in a pocket or compartment to find it in the early and chaotic first minutes of resuscitation. Easy access always promotes consistency in early use.

“So, Dr. G.: What kind of improvement have you seen in resuscitation practices in the EMS System for Metropolitan Oklahoma City and Tulsa since your crews started using these metronomes during cardiac arrest resuscitations?”

We made an assumption when the pit crew protocol was finalized and initially implemented, that the medics were providing 120 compressions per minute per our protocol. All of the involved agencies had metronomes at that time and there was nothing to lead us to believe this rate was in question.

When we participated in a cardiac arrest resuscitation analytics annotation pilot project sponsored by one of our industry partners in February and March of 2014, we found that the compression rates on some cases were alarmingly high while others were at or near 120. So we added a field to the data we collect and the CPR rates have been continuously tracked since that time.

One of the things we found early on was that some of the smaller sized metronomes were not being used for various reasons. In some cases, it was simply because the crews forgot to use them, though in others it was because the Velcro that had been used to attach them to the monitors had become worn and the metronomes either fell off and were lost, or they were simply placed in the monitor case where EMTs and paramedics didn’t know they were relocated. Like they say, out of sight can equal out of mind!

We also learned that environmental noise can cover the sound of the metronome, so, whatever metronome you use, it has to be capable of being heard and/or seen. The metronomes built into the cardiac monitor/defibrillators do seem to solve that problem, but I want to caution that I personally don’t think 100 compressions per minute for all cardiac arrest patients, in all resuscitation practices is the optimal rate as we know it today.

In all of the cases in our specific system when the metronome wasn’t used, the compression rate was certainly faster than the 120/min we desired. Interestingly, when the ambulance would go en route to the hospital, rates often jumped almost immediately from around 120 to 130 and above.

After we mounted a concerted effort to have the providers utilize the metronomes and began revealing the patterns in compression rates at our monthly CQI meetings and additionally in emails to the education departments in our system agencies, we found almost immediate elimination of extreme compression rate deviations (e.g., greater than 160/min).

Our typical rate is now 123/min. Keep in mind we’re still rolling out the change to 110/min. This is down from 129/min. It doesn’t sound like much, but there are nearly 100 workable arrests every month in our system and that’s a great achievement by our fire and EMS crews in focusing on hitting that compression “sweet spot” of compressions per minute. We believe it has strongly contributed in  increasing our successful resuscitations. 

“Thanks, Dr. G. Do you have any parting thoughts?”

It’s an exciting time in EMS resuscitation.  It takes work on everyone’s part to keep pace with the findings we’re putting into practice. Thanks for your commitment to excellence in out-of-hospital EMS medicine by reading this article. Together we’re finding better answers to challenges like cardiac arrest, answers that truly make a life or death difference to people we serve, and when they need those answers most. Keep reading and asking questions because scientific discoveries are happening in EMS medicine now more than ever. 

References

1. Field JM, Hazinski MF, Sayre MR, et al. Part 1: Executive summary: 2010 American Heart Association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care. Circulation. 2010;122(suppl 3):S640–S656.

2. Field RA, Soar J, Davies RP, et al. The impact of chest compression rates on quality of chest compressions: A manikin study. Resuscitation. 2012;83(3):360–364.

3. Jäntti H, Silfvast T, Turpeinen A, et al. Influence of chest compression rate guidance on the quality of cardiopulmonary resuscitation performed on manikins. Resuscitation. 2009;80(4):453–457.

4. Idris AH, Guffey D, Aufderheide TP, et al. The relationship between chest compression rates and outcomes from cardiac arrest. Circulation. 2012; 125(24):3004–3012.

5. Aufderheide TP, Nichol G, Rea TD, et al. A trial of an impedance threshold device in out-of-hospital cardiac arrest. N Engl J Med. 2011;365(9):798–806.

6. Aufderheide TP, Frascone RJ, Wayne MA, et al. Standard cardiopulmonary resuscitation versus active compression-decompression cardiopulmonary resuscitation with augmentation of negative intrathoracic pressure for out-of-hospital cardiac arrest: A randomized trial. Lancet. 2011;377(9762):271–352.

7. Kern KB, Stickney RE, Gallison L, et al. Metronome improves compression and ventilation rates during CPR on a manikin in a randomized trial. Resuscitation. 2010;81(2):206–210.