Abstract 223: What Affects Chest Compression Depth in Out-of-Hospital Cardiac Arrest?

Introduction: Adherence to CPR guidelines for chest compressions depth (CCD) is poor. Compressors tend to converge on an individualized depth for each patient.

Aim: Determine the factors affecting CCD in adult out-of-hospital cardiac arrest (OHCA).

Methods: Patient, event, and EMS characteristics extracted from a regional registry (age, sex, estimated weight, witness status, bystander AED use, location, time to reach patient, initial ECG rhythm, number of shocks delivered, advanced airway use, initial EtCO2, number of EMS responders) were linked to depth and stiffness (force/depth) data from CPR monitors of resuscitation efforts for adult OHCA collected by a first response agency in suburban Portland, Oregon during 2018-21. With generalized linear models we examined the relationship of case-wise CCD in relation to stiffness and arrest characteristics, as well as the determinants of stiffness, a dominant predictor of CCD. Significant univariate predictors (p < 0.05) were combined into multivariate models, where we assessed statistical significance with a limit of 0.05/(number of predictors).

Results: Case-wise median (IQR) chest compression depth was 50.3 (44.2 - 56.1) mm. Weight and stiffness dominated multivariate predictivity for depth (Table). Age had a modest effect overall and was not predictive in witnessed cases. Depth decreased with increasing stiffness and weight and increased slightly with age. Sex, weight and responder count were predictors of stiffness. Responder count did not predict initial stiffness. Stiffness increased with weight and decreased with number of responders.

Conclusions: Depth of chest compressions is best predicted by patient stiffness and weight. Age contributes little, sex is non-significant. Responders do not vary depth in relation to other arrest characteristics. Age, weight and number of responders were the best predictors of stiffness.