Chest compression release and recoil dynamics in prolonged manual cardiopulmonary resuscitation

Aim of the study: Characterize release and recoil dynamics in chest compressions during prolonged cardiopulmonary resuscitation (CPR) efforts, which are increasingly prevalent. Methods: Force and depth of chest compressions, and their rates of change, were calculated from records extracted from CPR monitors used during prolonged resuscitation efforts for out-of-hospital cardiac arrest and tracked over time. Metrics were normalized to the median of the first 100 compressions. Kruskal-Wallis ANOVA and Jonckheere-Terpstra trend analyses were used for differences and trends. Averages are reported as median (interquartile range). Correlations among metrics are reported as coefficients of determination. Results: In 471 cases of adult subjects receiving at least 1000 compressions, peak depths varied modestly over the course of extended resuscitation efforts, staying within a narrow range without a trend over the course of resuscitation efforts. Increases in recoil velocity and decreases in recoil interval also remained within limited ranges (5%, 6% variation respectively). By contrast, force waveforms changed substantially. Peak force decreased monotonically reaching a 38% decrease for compression numbers > 3500, similar to a decrease in release rate (39%) and an increase in release interval (39%). Conclusion: Depth waveforms change markedly less than do force waveforms over the course of prolonged CPR. With the benefit of feedback, CPR providers effectively adjust the application of force to compensate for changes in chest stiffness, documented previously. Despite slowing release and quickening recoil, interference between release of force and recoil of depth appears limited. Spontaneous chest recoil is well preserved in prolonged duration manual CPR.