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. 2022 Sep:178:96-101.
doi: 10.1016/j.resuscitation.2022.07.015. Epub 2022 Jul 16.

Investigating the Airway Opening Index during cardiopulmonary resuscitation

Shiv Bhandari  1 , Jason Coult  2 , Catherine R Counts  3 , Natalie E Bulger  4 , Heemun Kwok  4 , Andrew J Latimer  5 , Michael R Sayre  3 , Thomas D Rea  6 , Nicholas J Johnson  7
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Investigating the Airway Opening Index during cardiopulmonary resuscitation

Shiv Bhandari et al. Resuscitation. 2022 Sep.

Abstract

Introduction: Chest compressions during CPR induce oscillations in capnography (ETCO2) waveforms. Studies suggest ETCO2 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. ETCO2 and chest impedance waveforms were annotated for the presence of intubation and CPR. We developed four methods for computing AOI based on peak ETCO2 and the oscillations in ETCO2 during chest compressions (ΔETCO2). We examined the feasibility of automating ΔETCO2 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] ΔETCO2 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 ΔETCO2 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.

Keywords: Emergency Medical Services; End-tidal carbon dioxide; Out-of-hospital cardiac arrest; Respiration, Artificial.

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Conflict of interest statement

Conflicts of Interest NJJ receives funding from the National Institutes of Health, the Centers for Disease Control and Prevention, and University of Washington Royalty Research Fund and serves on the Scientific Advisory Board for Opticyte, LLC. JC receives funding by a grant provided to the University of Washington by the Washington Research Foundation. HK, MRS, and TDR receive funding provided to the University of Washington by the American Heart Association Strategically Focused Research Network on Arrhythmias and Sudden Cardiac Death.

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