The two most important things that we can do in cardiac arrest to improve survival and neurologically intact outcomes is high quality CPR, with limited interruptions and early defibrillation. The 2015 AHA/ACC CPR updates recommended a compression rate of 100 -120/min, a depth of 2 – 2.4in, allowing full recoil, and minimizing pauses. This is a lot to remember during a stressful code situation and one way many providers are offloading themselves cognitively is by the use of mechancical CPR (mCPR) devices.  In theory these devices compress at a fixed rate, and depth, with the added benefit that the machine simply does not tire out.  Additionally, use of this device allows another provider to be available for other procedures and interventions. A recent systematic review and meta-analysis in  looked at five randomized clinical trials with over 10,000 patients with out-of-hospital cardiac arrest (OHCA) (Gates 2015).  They concluded that there was no difference in ROSC, survival or survival with good neurological outcomes with the use of these devices compared to manual CPR. It is important to state that none of these studies showed increased harm either.  A new paper just published in Circulation however, argues that mCPR during OHCA was associated with lower neurologically intact survival.

Clinical Question

How does mCPR effect outcomes in OHCA?


Patients greater than or equal to 18 years of age with non-traumatic OHCA captured in the CARES US national registry.


Mechanical CPR


Manual CPR


Primary: Neurologically favorable survival at hospital discharge (Defined as Cerebral Performance Category of 1 or 2)


Retrospective study of data extracted from a national database


Age < 18, Traumatic arrest

Primary Results

  • 80,861 patients were included in the analysis
    • Median age was 62 years
    • 35.1% received bystander CPR

Critical Results (mCPR vs. Manual CPR)

  • Survival to Hospital Discharge: 7.0% vs. 11.3%
  • Neurologically Favorable Survival: 5.6% vs. 9.5%
  • Use of AED: 33.3% vs. 28.3%
  • Advanced Airway Placed: 87.4% vs. 79.0%
  • Impedance Threshold Device Used: 41.8% vs. 13.4%


  • Used a multivariable logistic regression model to control for arrest characteristics (Including: age, arrest location, bystander CPR, AED use, witnessed arrest status, initial rhythm, post arrest targeted temperature management, successful advanced airway placement, and impedance threshold device use)
  • Large, real life look at the use of mCPR in OHCA as opposed to prior work that was done in research setting
  • Primary outcome is clinically important and patient centered


  • Retrospective secondary analysis
  • Time of arrest, time of first CPR, and timing of interventions were not reliably reported
  • Interventions aside from mCPR not detailed here (with the exception of advanced airway and ITD)
  • Large variations in use of mCPR use by various EMS services (Ranged from 21.7% to >75% of OHCA cases)

Author's Conclusions

“In conclusion, the use of mCPR during out-of-hospital cardiac arrest was associated with lower neurologically favorable survival within emergency medical services agencies participating in CARES. Although the use of mCPR devices increased during the study period, deployment rates remained highly variable, and the majority of agencies did not use them. Further research is required to identify circumstances in which mCPR may benefit patients with out-of hospital cardiac arrest; however our data indicate that mCPR for routine cardiac arrest care was associated with worse outcomes.”

Our Conclusions

In this registry database of OHCA, the use of mCPR was associated with decreased survival and decreased survival with good neurologic outcomes. However, the retrospective nature of this study does not allow a full analysis of the causes of this difference.

Bottom Line

Although the authors of this paper must be commended for taking confounding variables into account in this large trial, it is retrospective and observational and therefore conclusions must be taken with a grain of salt. This is not the death of mCPR, but it is one of the first trials showing harm with the use mCPR in the prehospital setting.

Read More


Buckler DG et al. Association of Mechanical Cardiopulmonary Resuscitation Device Use With Cardiac Arrest Outcomes: A Population-Based Study Using the CARES Registry (Cardiac Arrest Registry to Enhance Survival). Circulation 2016; 134: 2131 – 2133. PMID: 27994028

Gates S et al. Mechanical Chest Compression for Out of Hospital Cardiac Arrest: Systematic Review and Meta-Analysis. Resuscitation 2015; 94: 91 – 7. PMID: 26190673