Abstract Body: Introduction: International guidelines support use of end-tidal carbon dioxide (E_TCO₂) for monitoring resuscitation in out-of-hospital cardiac arrest (OHCA). Specific E_TCO₂ cutoffs have been proposed for termination of resuscitation, though data on rates of ROSC based on changes in E_TCO₂ is limited. We aimed to evaluate the relationship between change in E_TCO₂ in OHCA and its relationship to return of spontaneous circulation (ROSC) using a US national database.

Methods: This retrospective analysis of National Emergency Medical Services Information System (NEMSIS) datasets from 2020 to 2022 evaluated all adult patients who underwent resuscitation for OHCA and had multiple E_TCO₂ measurements. We excluded cases with missing data. The highest difference between two sequential E_TCO₂ measurements (MΔE_TCO₂) and total difference between minimum and maximum E_TCO₂ measurements [TΔE_TCO₂] were calculated for each case. ΔE_TCO₂ groups were stratified into 10-unit increments and we compared rates of ROSC between groups. We then used multivariable logistic regression to evaluate the association between each 5 unit increase in ΔE_TCO₂ and ROSC. We adjusted for age, sex, location, witness status, initial shockable rhythm, and CPR or AED prior to EMS arrival.

Results: We included 274,516 total patients with 1,686,390 E_TCO₂ measurements. The median number of E_TCO₂ measurements was 5 (IQR 3-8). Median age was 65, 62.8% were male, 60.1% had witnessed arrests, and 78.3% received CPR and 32.3% received AED placement prior to EMS arrival. ROSC rates based on MΔE_TCO₂ were 0-10 mmHg [33.3%], 10-20 mmHg [42.3%], 20-30 mmHg [49.7%], 30-40 mmHg [53.2%], and >40 mmHg [56.6%]. ROSC rates for TΔE_TCO₂ were 0-10 mmHg [29.6%], 10-20 mmHg [36.7%], 20-30 mmHg [43.5%], 30-40 mmHg [48.9%], and >40 mmHg [54.6%]. Adjusted odds of ROSC per 10 mmHg increase in MΔE_TCO₂ was 1.21 [1.21-1.22] and TΔE_TCO₂ was 1.19 [1.19-1.19].

Conclusions: Increasing max and overall ΔE_TCO₂ was associated with increased rates and odds of ROSC for OHCA.