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Study: No Difference in Survival Between Continuous and Interrupted Chest Compressions in OHCA
Continuous compressions have long been thought of as superior to interrupted compressions with pauses for ventilations. But a recent study by Nichol, et al. suggests that if good quality CPR is performed, there may not be a difference in survival to discharge of out-of-hospital cardiac arrest patients between patients receiving either continuous and interrupted compressions. Despite this, in the prehospital environment, unexpected and unavoidable pauses in compressions occur often; therefore, prehospital providers may opt to continue to perform continuous compressions in order to mitigate these unavoidable pauses.
Introduction
Recently, a team led by the University of Washington's Graham Nichol, MD, published a randomized trial in the New England Journal of Medicine comparing continuous vs. interrupted chest compressions during cardiopulmonary resuscitation (CPR) for out of hospital cardiac arrest (OHCA) and found no difference in survival to discharge with favorable neurologic outcome.1
This challenges multiple previous observational studies showing a survival benefit with continuous compressions over interrupted compressions.2–5 Both groups in this large, randomized trial had good quality CPR as measured by chest compression rate, compression depth and compression fraction (CCF). This may explain the similar outcomes between the treatment arms and highlights the importance of good quality CPR in OHCA.
Quality CPR
In 1991 the Utstein variables were first proposed as a system of consistently reporting information about cardiac arrest resuscitations, but it was more than a system of reporting. They were demographic, temporal and practical variables known to be associated with cardiac arrest outcome including suspected cardiac vs. non-cardiac etiology, witnessed vs. non-witnessed arrest, initial rhythm and bystander CPR.6
Since then, as CPR interventions have advanced, several CPR performance variables have been found to also be associated with outcomes in cardiac arrest, including compression rate, compression depth, compression fraction, pre-shock pause, peri-shock pause and all breaks in CPR.7-12 More important, as was done in the Nichol, et al. study, recording these variables allows researchers to assess the relationship between interventions performed during CPR and patient outcomes.
The Nichol, et al. study randomized 23,711 OHCA patients into either a control group who received compressions interrupted by ventilations in a 30:2 ratio or an intervention group who received continuous uninterrupted compressions with either bag-valve mask (BVM) ventilations or passive oxygenation via non-rebreather mask. Both groups paused for rhythm analysis and shock (if indicated) about every two minutes and delayed advanced airway placement until about 6 minutes after the start of CPR, at which point both groups reverted to continuous compressions with BVM ventilations.1
As seen in Table 1, by comparing the CPR performance variables of the continuous vs. interrupted compression groups, it is clear why there was not a significant difference in survival to discharge. Each group had good CPR performance variables with averages that have been associated with improved cardiac arrest outcomes. These results reiterate that whether CPR performance targets are achieved via continuous or interrupted compressions, attaining these targets will result in improved outcomes.
Discussion
Despite these results, prehospital providers may elect to continue performing continuous compressions for several reasons. In addition to being one of the few interventions with a known survival benefit in OHCA,2–5 continuous compressions likely facilitate improved compression rates and compression fractions in suboptimal prehospital environments.
Although trials like the Nichol, et al. study prove that good quality CPR can be performed in the field, CPR quality is often poor.14 Pauses during extrication, transport, and to conduct other interventions like placing the patient on a defibrillator/monitor, intubating or obtaining IV/IO access are often unavoidable and unexpected, especially with a small prehospital crew. Because these pauses are often unavoidable and unexpected during CPR in the field, it fundamentally makes sense to continue compressions whenever possible and only stop for unpreventable obstacles.
Continuous compressions minimize the avoidable pauses, thereby mitigating the negative effects the unavoidable pauses would have on compression rate and compression fraction. Mitigating these pauses is one mechanism explaining why interventions like minimally interrupted cardiac resuscitation (MICR), which includes continuous compressions, single shocks, immediate post-shock compressions and delayed intubation, have previously shown survival benefit in OHCA.2
Lastly, as seen in Table S1 of the Supplementary Appendix, the Nichol, et al. study selected cardiac arrests with high mean compression fractions in both groups: >80% in the continuous compression group and between 60-80% in the interrupted compression group. This created some selection bias in the sample population against cardiac arrests with lengthy pauses in compressions, which is the subgroup of cardiac arrests that would likely benefit most from continuous compressions.1
Potential Pitfalls
There are some pitfalls to avoid when performing continuous compressions:
- Although the Nichol, et al. study did not address ventilation rates or tidal volume, continuous compressions can facilitate hyperventilation. Maintaining an appropriate ventilation rate utilizing the 1 breath every 6 seconds method is difficult and multiple studies have shown that hyperventilation with this method is common and detrimental.15–19 However, several commonly used adjuncts are available to mitigate hyperventilation, including compression-adjusted ventilations, metronomes, and CPR feedback devices.20
- Compression-only CPR may facilitate a compression rate that is too fast. Ahamed Idris, MD, et al. found that in about 1/3 of CPR cases compression rates exceeded 120/min, while in 7% of cases they exceeded 140/min. They also found that the likelihood of ROSC peaked at about 125/min and declined at greater rates.7,12
- Excessive compression rates have been associated with inadequate compression depths, potentially explaining negative outcomes with elevated rates.12,21
Conclusion
High-quality resuscitation trials through research networks such as ROC have helped to deeper our understanding of the impact each intervention we provide during CPR may have on patients. Regardless of the CPR technique employed (continuous or briefly interrupted), lengthy breaks in CPR for other aspects of resuscitation may be detrimental and should be avoided. The Nichol et al. study reinforces that good quality CPR with adequate compression rates, compression fraction, compression depth and minimal pauses is essential if we are to maximize the benefit we provide to our OHCA patients.
References
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16. Aufderheide TP and Lurie KG. Death by hyperventilation: A common and life-threatening problem during cardiopulmonary resuscitation. Crit Care Med, 2004;32(9): S345–S351.
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17. Cheifetz IM, Craig DM, Quick G, et al. Increasing tidal volumes and pulmonary overdistention adversely affect pulmonary vascular mechanics and cardiac output in a pediatric swine model. Crit Care Med, 1998;26(4):710–716.
19. Theres H, Binkau J, Laule M, et al. Phase-related changes in right ventricular cardiac output under volume-controlled mechanical ventilation with positive end-expiratory pressure. Crit Care Med, 1999;27(5):953–958.
20. Nikolla D, Lewandowski T, Carlson J. Mitigating hyperventilation during cardiopulmonary resuscitation. Am J Emerg Med, 2016 Mar;34(3):643–6.
21. Chung TN, Bae J, Kim EC, et al. Induction of a shorter compression phase is correlated with a deeper chest compression during metronome-guided cardiopulmonary resuscitation: a manikin study. Emerg Med J, 2013 Jul;30(7):551–554.
Dhimitri Nikolla, DO, EMT-B, is an emergency medicine resident physician at Allegheny Health Network—Saint Vincent Health Center in Erie, PA. He continues to volunteer as an EMT-B at Tuxedo Volunteer Ambulance Corps in Tuxedo, NY. Contact him at dhimitri.nikolla@med.lecom.edu.
Jestin N Carlson, MD, MSc, is an emergency medicine attending physician at Allegheny Health Network–Saint Vincent Health Center in Erie, PA. He is the resident research director and core faculty for the Saint Vincent osteopathic emergency medicine residency.
