Abstract 131: Chest Molding in Extended Cardiopulmonary Resuscitation

Abstract

Introduction: Cardiopulmonary resuscitation (CPR) is a forceful procedure that may change characteristics of the subject. Little clinical data has been published relating applied forces and depth responses, particularly in increasingly prevalent extended sessions of CPR. We analyzed synchronous force and depth records to investigate how chests mold during the course of extended CPR. Hypothesis: Chest molding, characterized as decrease in stiffness from its initial value, will increase as CPR proceeds. Methods: Force and acceleration signals were extracted from CPR monitors used in adult cases of continuous compression CPR in out-of-hospital resuscitations attended by a single EMS agency (TVFR, Tigard, Oregon) during 2013 through 2017. We computed depth and velocity from acceleration, and identified chest compressions automatically where downward velocity crossed 25mm/s and force subsequently exceeded 5 kg-f. Series were defined as sequences without pauses exceeding 2 minutes. We analyzed initial series lasting at least 10 minutes. We calculated stiffness as force/depth at peak compression velocity. We calculated molding in 5 minute blocks of CPR as 100*(1- stiffnessblock/stiffnessminute 1), using medians as stiffness was not normally distributed. Dependence of molding on CPR duration was analyzed with Kruskal-Wallis ANOVA. Results and Conclusions: Of 616 available cases, 478 had initial CPR series >= 10 minutes duration, including 997,254 compressions. Initial CPR series duration were >= 30 minutes in 152 cases, and >= 40 minutes in 48 cases. The longest initial series was 61 minutes. Chest molding increased steadily through the first 25 minutes of CPR, and plateaued thereafter (p < 0.001). Median molding at >= 25 minutes was 20%. The implications of declining stiffness warrant further investigation.