Automated Chest Compression Devices
August 1, 2006 6 minutes read
Automated Chest Compression Devices
Abstracts & Commentary
By John P. DiMarco, MD, PhD, Professor of Medicine, Division of Cardiology, University of Virginia, Charlottesville. Dr. DiMarco is a consultant for Novartis, and does research for Medtronic and Guidant.
Synopsis: Even a device which makes perfect physiological sense may not help us achieve the goals of improved outcomes for out-of-hospital cardiac arrest victims.
Sources: Hallstrom A, et al. Manual Chest Compression vs Use of an Automated Chest Compression Device During Resuscitation following Out-of-Hospital Cardiac Arrest: A Randomized Trial. JAMA. 2006;295:2620-2628; Ong ME, et al. Use of an Automated, Load-Distributing Band Chest Compression Device for Out-of-Hospital Cardiac Arrest Resuscitation. JAMA. 2006;295:2629-2637.
Rates of resuscitation after out-of-hospital cardiac arrest remain disappointing. Recently, 2 papers reporting the use of a new device for performing chest compression during cardiopulmonary resuscitation (CPR) were published.
The first study was a multi-center, randomized, cluster trial of patients with out-of-hospital cardiac arrest conducted at 5 centers in the United States and Canada. The device used was the AutoPulse Resuscitation System (ZOLL Circulation, Sunnyvale, CA). This device is a load-distributing band (LDB) circumferential chest compression device. The constricting band is electrically actuated on a short backboard, and has been shown to produce greater blood flow to the heart and brain than manual CPR or some other automated CPR device. In this trial, Emergency Medicine System (EMS) stations at each study site used the LDB-CPR device during alternate periods of time. The cross-over between standard CPR and LDB-CPR occurred at each center at intervals of 4 weeks to 2 months.
Prior to the study, there was a brief run-in period during which EMS personnel integrated use of the LDB-CPR device into their out-of-hospital care routine. All EMS personnel underwent hands-on skill practice before the study. Several minor variations in treatment immediately after arrival of EMS personnel were permitted by the protocol to conform with local preferences. Patients randomized to standard manual CPR received manual CPR, according to published guidelines. Patients randomized to the LDB-CPR received compressions from the device at a rate of 80 per minute, either with or without intermittent pauses for ventilation. The primary end point of the study was survival, with spontaneous circulation 4 hours after the 911 call. Secondary end points included discharge from the hospital and cerebral performance category score at the time of discharge.
During the randomization period, there were 673 total cases assigned to manual CPR and 704 total cases assigned to LDB-CPR. Prespecified exclusion criteria left 517 eligible cases in the manual CPR group and 554 eligible cases in the LDB-CPR group. After exclusion of patients who had cardiac arrest after EMS arrival, a noncardiac etiology for the arrest or more than 90 seconds of advanced life support before the study ambulance arrived, there were 373 primary comparison episodes in the manual CPR group and 394 primary comparison episodes in the LDB-CPR group. There were only minor clinical differences between the groups. In the total population, 19% of the arrests occurred in a public location and the mean age of victims was 66 years. Sixty-five percent were men. The initial rhythm was VF or pulseless VT in 31%, pulseless electrical activity in 22.5%, asystole in 41%, and uncertain in the remainder. Time from the first 911 call to the first EMS vehicle arrival was 5.6 minutes, and to study vehicle arrival was 6.7 minutes. Initiation of chest compressions using the LDB-CPR device began a mean of 11.9 minutes after the 911 call.
There was no significant difference in survival at 4 hours after the 911 call between the manual CPR group and the automated LDB-CPR group (24.7% vs 26.4%). Survival at hospital discharge was lower in the LDB-CPR group (5.8% vs 9.9%). Survival with a cerebral performance category score of 1 or 2 was observed in 7.5% of patients in the manual CPR group compared with 3.1% in the LDB-CPR group. Adjustment for differences in clinical characteristics and treatment site revealed similar patterns of survival. Based on these data, the Data Safety Monitoring Board, after a review of interim data, recommended discontinuation of the study.
The second study also used the AutoPulse LDB-CPR device. The study was performed in a single EMS system (Richmond, VA) and used a historical control group for comparison. The manual CPR phase was between January 2001 and March 2003. There was, then, an interim period during which LDB-CPR units were evaluated and introduced into the system. The LDB-CPR phase was between December 2003 and March 2005. In the Richmond EMS systems, the first responders were paramedics who were trained to provide 90 seconds of CPR before defibrillation. This continued before and after introduction of the LDB-CPR system, with manual CPR performed until the LDB-CPR device could be set up and activated. This was only an option in the multicenter trial discussed earlier. The primary outcome measure was return of spontaneous circulation. Secondary outcomes included survival rates to both hospital admission and hospital discharge and neurological status at discharge.
During the manual CPR phase, there were 1475 patients with out-of-hospital arrest. Resuscitation was attempted in 657 individuals, and 499 had a presumed cardiac etiology. During the LDB-CPR phase, there were 284 patients with a presumed cardiology etiology, but 74 did not have the LDB-CPR device applied. Patient characteristics during the 2 phases of the study were similar except that slightly higher proportions of subjects had their cardiac arrest witnessed by the EMS team in the LDB-CPR group. The EMS response time was also slightly shorter in the LDB-CPR phase, and a small number of patients in that group received hypothermia as post-resuscitation treatment.
Return of spontaneous circulation was seen in 34.5% of the LDB-CPR group in comparison to 20.2% of the manual CPR group. Survival-to-hospital admission (20.9% vs 11.1%) and survival-to-hospital discharge (9.7% vs 2.9%), respectively, were also both improved in the LDB-CPR phase of the study. All of the benefits of LDB-CPR compared to manual CPR occurred in those arrests when the paramedic ambulances arrived on location in less than 8 minutes from the time of the 911 call.
The authors conclude that a resuscitation strategy employing the LDB-CPR device results in improved outcomes in out-of-hospital cardiac arrest.
Commentary
Studies on resuscitation strategies for out-of-hospital cardiac arrest victims are notoriously difficult to conduct. It has been clearly shown that prompt external defibrillation improves survival in patients with ventricular fibrillation and pulseless ventricular tachycardia. It has been estimated that the probability of survival decreases with each minute before defibrillation. Standard manual CPR has also been shown to extend the window for survival by a short time. It has, however, been well shown that CPR is difficult to perform consistently, even by trained personnel. This has led to the development of external devices such as the LDB-CPR device used in these studies. The hope has been that better CPR would result in improved survival rates.
The reason why these 2 studies had different results remains uncertain. The study by Ong and colleagues was not a randomized trial, and is subject to temporal changes that might have affected the results. The randomized trial by Hallstrom and colleagues was performed simultaneously at 5 centers, thus avoiding any temporal bias, but sight changes in the 2 EMS treatment protocols make comparison of the 2 studies difficult. What can be said definitely is that the rates for survival with a good neurological outcome remained poor in all groups in both studies.
The LBD-CPR system described in these studies has been approved for commercial use by the FDA and is currently used by many EMS systems. In the future, we can hope that the FDA will require careful post-marketing studies of devices such as theses. The studies here show that even a device which makes perfect physiological sense may not help us achieve the goals of improved outcomes for out-of-hospital cardiac arrest victims.
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