ABSTRACT & COMMENTARY
Mechanical Chest Compressions in CPR
By Michael H. Crawford, MD
Professor of Medicine, Chief of Clinical Cardiology, University of California, San Francisco
This article originally appeared in the March 2014 issue of Clinical Cardiology Alert. It was peer reviewed by Ethan Weiss, MD, Assistant Professor of Medicine, Division of Cardiology and CVRI, University of California, San Francisco. Dr. Crawford reports no financial relationships relevant to this field of study, and Dr. Weiss is a scientific advisory board member for Bionovo.
Source: Rubertsson S, et al. Mechanical chest compressions and simultaneous defibrillation vs conventional cardiopulmonary resuscitation in out-of-hospital cardiac arrest: The LINC randomized trial. JAMA 2014;311:53-61.
Effective cardiopulmonary resuscitation (CPR) is partly dependent on the adequacy of manual chest compressions, but they are limited by interruptions and less than ideal conditions such as during transport. Mechanical chest compression devices have been developed that improve organ perfusion vs manual compressions in experimental studies, but there is little evidence of their clinical effectiveness and safety compared to manual compressions. Thus, these investigators from Sweden, the Netherlands, and the United Kingdom conducted a randomized trial to compare whether CPR using a mechanical chest compression device (LUCAS) resulted in superior 4-hour survival in patients with out-of-hospital cardiac arrest as compared to standard CPR with manual chest compressions. All patients in whom CPR was performed by six emergency medical systems in three countries between January 2008 to August 2012 were entered. Exclusion criteria were traumatic cardiac arrest, known pregnancy, age < 18 years, or body size inappropriate for the device (too large or small). Several secondary outcomes were evaluated, including survival with good neurologic outcome at 6 months.
A total of 4998 cases were screened and 2593 were enrolled. Informed consent was done after successful resuscitation and four patients withdrew consent, leaving 2589 study subjects. The first defibrillation was delivered 1.5 minutes later and there were more defibrillations in the mechanical compression group, but otherwise the groups were well matched. The primary outcome of survival to 4 hours was not different between the two groups (both 24%). Nor was there a significant difference in any of the secondary outcomes. There were 23 device-related adverse events among 1282 deployments of the device and eight of these required discontinuing use of the device. There were seven serious adverse events with the device vs three with manual compressions; these included pneumothorax and flail chest. The authors concluded that there was no significant difference in 4-hour post out-of-hospital cardiac arrest survival between those in whom a mechanical chest compression device was used vs. manual compressions during CPR.
This seems to be the glass half full or empty parable. One could look at this study and conclude that these mechanical chest compression devices are not worth buying or could say that they are just as good as the manual way, so what could an emergency medical technician (EMT) do to benefit the arrest victim if he/she is not pushing on the chest. Also, they produce consistent excellent chest compressions with a compression fraction of 0.84 vs 0.78 for manual. So, this might allow highly skilled but smaller people with less arm strength to be EMTs. One of my colleagues was urging us to buy these devices because he didn't want a small relatively weak resident doing chest compressions on him when he collapses during rounds (he is a large man). In addition, these devices seem safe; serious complications from the device were unusual and not statistically different from manual compressions. Also, device malfunction was rare (< 1%). There were issues with very large and small people with device fit, but overall it fit 95% of people. This could easily be corrected by having different sized devices or other technical improvements.
Given all these pluses, why didn't use of this device improve outcomes? There are several plausible reasons. First, the device group's CPR protocol was different to try to take advantage of the device's strengths. Chest compressions were done in 3-minute intervals rather than 2 minutes with manual compressions to take advantage of the lack of fatigue with the device. Second, the first defibrillation shock was given without stopping compressions in the device group, again to take advantage of the automatic chest compressions without human contact with the victim during the shocks. Third, since compressions were not stopped for the first shock, it was given as quickly as possible without efforts to determine the patient's rhythm. Fourth, the first shock was delivered 1.5 minutes later in the device group due to the time needed to employ the device. Finally, since this study was done in the field by EMS personnel, it is likely that all the EMTs were excellent at chest compressions, which may not be the case in less selective environments. Which of these potential explanations for the failure to show better outcomes with the device is the most important is difficult to determine. However, I believe the device has promise and is at least as good as manual compressions. Further work to capitalize on the advantages of mechanical chest compressions seems warranted. If your CPR results aren't what you want them to be, perhaps looking into deploying a mechanical chest compression device makes sense.