Abstract 205: Variability of Chest Compression Duty Cycle in the Treatment of Out-of-Hospital Cardiac Arrest

Abstract

Background: The duty cycle (DC) of cardiopulmonary resuscitation (CPR), which, from the start of one compression to the start of the next compression, describes the proportion of time spent compressing the chest downward, may be useful for characterizing CPR quality. Fifty percent is considered an optimal CPR DC, but little is known about real world DC characteristics. Objective: To describe DC characteristics of CPR delivered during the treatment of out-of-hospital cardiac arrest (OHCA). Methods: Defibrillator download files for cases of OHCA treated by emergency medical services (EMS) between 2006 and 2008 were obtained from the Pittsburgh regional clinical center of the Resuscitation Outcomes Consortium (ROC), a multi-center clinical research network. Compression depth data were imported into custom software, screened for artifacts, and then parsed and analyzed to establish start, end, and maximum depth for each compression. DC was calculated as the proportion of a compression prior to maximum depth. Descriptive statistics were reported for compression depth in centimeters, rate in compressions per minute (CPM) and DC, averaged over each minute of CPR for up to 30 minutes. Generalized estimating equations (GEE) were used to model the relationship between DC and rate, depth and time. Results: The 328 cases included in this study had a mean (SD) age of 64.9 (16.7) years and were predominantly male (61.9%, SE: 2.7). A total of 393,013 analyzable compressions were detected. Figure 1 shows the average CPR DC, rate and depth over the first 30 minutes. Average DC for this period ranged from 44.0% to 46.7%. Mean (SD) DC for the entire 30 minute period was 45.6% (5.2). In a GEE model, DC was inversely related to rate (coeff: -0.0004, p<0.001) and time (coeff: -0.0006, p<0.001), but directly related to depth (coeff: 0.0038, p<0.001). Conclusions: DC in EMS-treated OHCA cases was less than the 50% standard, decreased over time, and correlated with both compression rate and depth.