Investigating the Airway Opening Index during cardiopulmonary resuscitation

Introduction: Chest compressions during CPR induce oscillations in capnography (E_TCO₂) waveforms. Studies suggest E_TCO₂ oscillation characteristics are associated with intrathoracic airflow dependent on airway patency. Oscillations can be quantified by the Airway Opening Index (AOI). We sought to evaluate multiple methods of computing AOI and their association with return of spontaneous circulation (ROSC).

Methods: We conducted a retrospective study of 307 out-of-hospital cardiac arrest (OHCA) cases in Seattle, WA during 2019. E_TCO₂ and chest impedance waveforms were annotated for the presence of intubation and CPR. We developed four methods for computing AOI based on peak E_TCO₂ and the oscillations in E_TCO₂ during chest compressions (ΔE_TCO₂). We examined the feasibility of automating ΔE_TCO₂ and AOI calculation and evaluated differences in AOI across the methods using nonparametric testing (α = 0.05).

Results: Median [interquartile range] AOI across all cases using Methods 1-4 was 28.0 % [17.9-45.5 %], 20.6 % [13.0-36.6 %], 18.3 % [11.4-30.4 %], and 22.4 % [12.8-38.5 %], respectively (p < 0.001). Cases with ROSC had a higher median AOI than those without ROSC across all methods, though not statistically significant. Cases with ROSC had a significantly higher median [interquartile range] ΔE_TCO₂ of 7.3 mmHg [4.5-13.6 mmHg] compared to those without ROSC (4.8 mmHg [2.6-9.1 mmHg], p < 0.001).

Conclusion: We calculated AOI using four proposed methods resulting in significantly different AOI. Additionally, AOI and ΔE_TCO₂ were larger in cases achieving ROSC. Further investigation is required to characterize AOI's ability to predict OHCA outcomes, and whether this information can improve resuscitation care.