Recent CPR Findings Raise New Questions

The recent AHA and ILCOR CPR guidelines and ROC trial findings codified important, current knowledge about CPR. Yet resuscitation research continues to be fraught with difficulty, and physicians need to recognize its limitations.

A few years ago, we celebrated an important 50th anniversary: the advent of closed-chest cardiopulmonary massage was published in JAMA in 1960 by Kouwenhoven, Jude and Knickerbocker [1]. Fast forward to 2015 and it is interesting that we are still working on the details of this amazing advance in medicine.

The ensuing decades produced extensive research on the best treatment of sudden cardiac death. We have studied drugs, tools and techniques and have created an industry that brings the best and latest techniques to the medical and lay community, even though the evidence is often anecdotal or scant. Since the recommendations seem to change on a frequent basis, many of us have trouble keeping up with what really is best. We do know that of all of the drugs, tubes and mechanical devices we’ve assessed through the years, the only certain thing is that early effective CPR saves lives and that better CPR saves lives better. And yet we are still far from sure of the best way to apply chest compressions and ventilation.

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We can now unequivocally define the important parameters of “high performance CPR”: adequate depth (at least 2 inches), complete recoil of the chest, adequate rate (probably about 110/min) and a chest compression fraction or CCF (proportion of each minute chest compressions are being applied) of greater than 60% (per guidelines, but most of us have much higher goals of around 90) [2], minimize pauses and don’t over-ventilate. But do you need to ventilate at all [3]? If so, how much and how frequently? We are pretty sure that pauses in CPR can be fatal [4,5], but maybe short pauses for ventilation are necessary or superior?

2015 CPR Guidelines already outdated by ROC?
The 2015 AHA and ILCOR guidelines [6,7,8] are hot off the press. The AHA guidelines endorse a strategy of continuous compressions with “asynchronous” ventilations during CPR in patients with an advanced airway, that is, breaths interposed every six seconds without interruption in CPR—OR 10 breaths/minute without stopping CPR. For 1 and 2 rescuer CPR in adults they recommend interrupted compressions with thirty compressions followed by 2 breaths (30:2) during which chest compressions are withheld, consistent as well with the recommendations of ILCOR. These guidelines were based upon the best evidence available at the time of 2015 guideline development.

Now, on the heels of the recommendations is an important large study conducted by the Resuscitation Outcomes Consortion (ROC) that compares continuous chest compressions with asynchronous BVM ventilation (the study intervention) against CPR with compression pauses for breaths (the study control) in patients without an advanced airway placed.

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ROC is a well-seasoned research network that has been performing out of hospital resuscitation research for the last decade. Study centers provide high quality CPR and performance is measured through the use of recording monitor defibrillators. In the NEJM-reported trial [9], 8 clinical sites representing 114 EMS agencies enrolled 23,711 patients. So what was the conclusion?

The ROC study concluded that there was no significant difference between the two techniques with regard to survival to discharge. In the asynchronous ventilation group, overall survival was 9.7% (7.7% with most favorable neurological outcome) versus 9.0% in the continuous compression group (7% with most favorable outcome). This was the outcome for all comers, all rhythms and with ventricular fibrillation accounting for only about 22% in both groups.

While the study seems to support that interrupted or continuous compressions lead to statistically similar outcomes, the problem is that close reading of the particulars of the study may not support that conclusion. The very important detail is that in this trial, the expected difference in compression fractions with continuous versus interrupted CPR was not found. Both groups had an approximate 80% CCF. Why is this so important? The benefit we hope will accrue by doing continuous compressions is a higher percentage of time during CPR that chest compressions are being performed, the so-called chest compression fraction, CCF. Unfortunately the study showed only a slight and non-significant difference in the chest compression fractions between the groups. If the compression fraction between the groups is not significantly different then a valid concern is whether they truly discriminated between the two methods.

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We are therefore left with considering that the potential implication is that this study revalidates the effect of compression fraction more than the benefit of one ventilation strategy over the other. In other words, like compression fractions led to like results.

For those with a research bent, glance at the study and note that when the groups were compared after subselection by an algorithm for patients that clearly met the “machine” criteria for either continuous versus interrupted CPR, a significant survival advantage was found for interrupted. However, these groups were no longer statistically balanced and once this correction was added the difference did not persist. Tantalizing but not scientifcally proven!

Resuscitation research is very difficult. The ROC has for years provided a platform for investigating causation as opposed to association in the details of the components of critical interventions in various types of resuscitation. This meticulous study provides important information for us regarding ventilation strategy in CPR but it also demonstrates the limitations inherent in studies of out of hospital cardiac arrest, which is the sine qua non of complex multivariable events.

The Bottom Line For Best Outcomes
Either continuous chest compressions or chest compressions interrupted with ventilation are OK as long as meticulous basic CPR technique is followed and perishock pauses are kept as brief as possible.

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In light of the recent ROC trial and new adult ACLS guidelines, here are the numbers you need to know:

• 110 compressions per minute
• 2-2.4 inches chest compression
• 30:2 (1 breath q 6s) OR continuous compressions with asynchronous ventilation
• At least 60% (try for 90%) of resuscitation should be chest compressions.
• Keep pauses as short as possible

REFERENCES

1. KouwenhovenWB, JudeJR, KnickerbockerGG  Closed-chest cardiac massage  JAMA 1960, 173(10):1064-1067. Doi: 10.100/JAMA 1960.03020280004002
2. Christensen J, Andrusiek D et al. Chest compression fraction determines survival in patients with out-of-hospital ventricular fibrillation. Circulation 2009; 120:1241-1247
3. Bobrow BJ, Clark LL, Ewy GA, et al. Minimally interrupted cardiac resuscitation by emergency medical services for out-of-hospital cardiac arrest. JAMA 2008;299:1158-1165
4. Berg RA, Sanders AB, Kern KB, et al. Adverse hemodynamic effects of interrupting chest compressions for rescue breathing during cardiopulmonary resuscitation for ventricular fibrillation cardiac arrest. Circulation 2001;104:2465-2470
5. BrouwerTF, WalkerRG et al. Association between chest compression interruptions and clinical outcomes of ventricular fibrillation out of hospital cardiac arrest CIRCULATIONAHA.115.014016 Published online before print August 7, 2015, doi: 10.1161/CIRCULATIONAHA.115.014016
6. O’Connor RE, Al Ali AS, Brady WJ et al 2015 American Heart Association Guidelines Update for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care.  Circulation  Nov 3, 2015 132: 18 (supplement 2), s483-500
7. Perkins GD, Handley AJ, Koster RW et al ‘European Resuscitation Council Guidelines for Resuscitation 2015: Section 2. Adult Basic life Support and Automated External Defibrillation, Resuscitation, 95: 81-99, October 2015
8. Monsieurs KG, Nolan JP, Bossaert LL et al ‘European Resuscitation Council Guidelines for Resuscitation 2015: Section 1. Executive Summary. Resuscitation, 95:1-80, October 2015
9. Nichol G, Leroux B, Wang H, et al. Trial of continuous or interrupted chest compressions during CPR. N Engl J Med. Dec 3 2015 ; 373:2203-2214 PMID 26550795 DOI: 10.1056/NEJMoa1509139