Can chest compression release rate or recoil velocity identify rescuer leaning in out-of-hospital cardiopulmonary resuscitation?

Background: Measurement of chest velocity has been proposed as an alternative method to identify responder leaning during cardiopulmonary resuscitation (CPR). Leaning is defined in terms of force, but no study has tested the utility of chest velocity in the presence of force measurements that directly measure leaning. Materials and methods: We analyzed 1004 out-of-hospital cardiac arrest (OHCA) files collected with Q-CPR monitors in the Portland, Oregon, USA metro region from 2006 to 2017. Records contained accelerometry and force signals. For each chest compression, the following metrics were computed: minimum force at the end of the compression (F-release), compression depth, compression rate, maximum chest velocity during recoil (v(recoil)) and maximum rate of change in force during chest release (upsilon(release)). A compression was classified as having leaning if F-release was greater than 2.5 kg-f. The ability of v(recoil) and upsilon(release) to predict F-release was estimated with generalized linear models, and their ability to identify leaning with logistic regression. Results: The data set contained over 1.5 million chest compressions, 21% compliant with 2015 rate and depth guidelines for CPR (the G2015 population). Leaning was uncommon generally (12%), and less common in G2015 compliant compressions (5%). Leaning and F-release decreased with both vrecoil and.release but with extensive overlap. Neither v(recoil) nor upsilon(release), alone or in combination with chest compression rate and depth, reliably predicted leaning or F-release. Conclusion: Leaning cannot be reliably identified from v(recoil) or upsilon(release), alone or in combination with currently recommended chest compression metrics in out-of-hospital CPR.