Resuscitation From Out-of-Hospital Cardiac Arrest: When Is EtCO2 Reliably Associated With ROSC?
Circulation · 2026-05-18 · Observational study
Abstract
BACKGROUND: Exhaled end-tidal carbon dioxide (EtCO2) trajectory is associated with out-of-hospital cardiac arrest (OHCA) outcomes. However, the minimum EtCO2 monitoring duration needed to discriminate return of spontaneous circulation (ROSC) from non-ROSC remains unknown. We sought to determine the EtCO2 trajectory observation time required to differentiate ROSC from non-ROSC patients. METHODS: We performed a secondary analysis of the cluster-randomized Pragmatic Airway Resuscitation Trial (PART), which assessed endotracheal intubation or laryngeal tube strategies in OHCA resuscitation. We summarized mean EtCO2 in 1-minute epochs over the resuscitation. Cases were stratified a priori by: (1) witnessed versus unwitnessed status, and (2) initial EtCO2: low (≤30 mm Hg), moderate (31-49), and high (≥50). Within each stratum, group-based trajectory modeling (GBTM) was used to identify latent EtCO2 trajectory classes, and patients were categorized into an upward or downward trajectory. To balance trajectory groups on baseline characteristics including age, sex, race, initial rhythm, location, and bystander CPR, we applied inverse probability of treatment weighting. We fit weighted pooled logistic regression models to estimate risk ratios (RRs) for ROSC comparing upward versus downward EtCO2 trajectories. Within each stratum, we identified the earliest minute when CIs between upward versus downward EtCO2 trajectories no longer overlapped. RESULTS: EtCO2 data were available for 1168 patients: 452 (38.6%) witnessed and 716 (61.1%) unwitnessed. Patients were predominantly men (63.5%), with a median age of 65 years (Q1, Q3: 53-75), majority White race (51.3%), and presenting in a nonpublic setting (85.4%). Overall ROSC was 18.2%: 30.5% of witnessed and 10.5% of unwitnessed. Among witnessed arrests, 95% CI for upward versus downward EtCO2 trajectories no longer overlapped at 8 minutes for low initial EtCO2 (RR, 3.06; 95% CI, 1.49, 6.71), 12 minutes for moderate EtCO2 (RR, 1.95; 95% CI, 1.23, 3.48), and 21 minutes for high EtCO2 (RR, 2.12; 95% CI, 1.30, 3.73). Among unwitnessed arrests, nonoverlapping CIs were first observed at 7 minutes (RR, 3.56; 95% CI, 1.53, 10.37). CONCLUSIONS: Depending on witness status and initial EtCO2, between 7 and 21 minutes of monitoring are needed to reliably differentiate upward from downward EtCO2 trajectories during OHCA resuscitation. Dynamic EtCO2 trajectory monitoring may provide early prognostic information to guide resuscitation.