Transthoracic impedance variability to assess quality of chest compression in out-of-hospital cardiac arrest

Background: Chest compression is a lifesaving intervention in out-of-hospital cardiac arrest (OHCA), but the optimal metrics to assess its quality have yet to be identified. The objective of this study was to investigate whether a new parameter, that is, the variability of the chest compression-generated transthoracic impedance (TTI), namely ImpCC, which measures the consistency of the chest compression maneuver, relates to resuscitation outcome. Methods: This multicenter observational, retrospective study included OHCAs with shockable rhythm. ImpCC variability was evaluated with the power spectral density analysis of the TTI. Multivariate regression model was used to examine the impact of ImpCC variability on defibrillation success. Secondary outcome measures were return of spontaneous circulation and survival. Results: Among 835 treated OHCAs, 680 met inclusion criteria and 565 matched long-term outcomes. ImpCC was significantly higher in patients with unsuccessful defibrillation compared to those with successful defibrillation (p =.0002). Lower ImpCC variability was associated with successful defibrillation with an odds ratio (OR) of 0.993 (95% confidence interval [95% CI], 0.989–0.998, p =.003), while the standard chest compression fraction (CCF) was not associated (OR 1.008 [95 % CI, 0.992–1.026, p =.33]). Neither ImpCC nor CCF was associated with long-term outcomes. Conclusions: In this population, consistency of chest compression maneuver, measured by variability in TTI, was an independent predictor of defibrillation outcome. ImpCC may be a useful novel metrics for improving quality of care in OHCA.