Abstract 236: Complete Recoil Duration Declines Over the Course of Longer Resuscitations

Abstract

Introduction: CPR guidelines call for chest compressions within rate and depth ranges and complete chest recoil. Guidelines development has relied on data from the first 10 minutes of resuscitations. We investigated the influence of rate, depth and chest stiffness on complete recoil duration in longer resuscitations. Hypothesis: Decreasing chest stiffness will contribute to reduced complete recoil duration over the course of long resuscitations. Methods: Acceleration and force signals were from monitors used in continuous compression CPR during out-of-hospital resuscitations of adults treated by Tualatin Valley Fire & Rescue (Tigard, OR) from 2013 through 2017. Complete recoil was defined as return to within 5 mm of baseline in the absence of leaning (release force > 2.5 kg-f), stiffness as peak force/peak depth. Influences of rate, depth and stiffness on complete recoil duration were modeled with linear mixed effects models with a random intercept and slope clustered by patient. Results: A total of 1,076,808 compressions without leaning (93% of compressions) were measured from 616 cases with 1888 ± 1118 compressions/case (mean ± std). Observed increases in rate (7%) and depth (2%) were modest, while stiffness declined markedly (-33%) (Fig 1a). All of these changes tend to reduce the duration of complete recoil (p < 0.001). Mean complete recoil duration decreased 21% (Fig 1a) from 160 ms to 126 ms (Fig 1b). Despite its large relative change, stiffness had little effect on complete recoil duration, as did depth. Increasing rate explained most of the decline in complete recoil duration (Fig 1b). Conclusions: Substantial decline in chest stiffness over the course of long resuscitations contributes to reduction of complete recoil duration but little compared to increasing rate. Careful compliance with rate guidelines is paramount in maintaining periods of complete recoil. Depth is relatively well-controlled. Chest molding (decreased stiffness) is of secondary importance.