We investigated the predictive value of the gradient between arterial carbon dioxide (PaCO₂) and end-tidal carbon dioxide (ETCO₂) (Pa-ETCO₂) in post-cardiac arrest patients for in-hospital mortality.

This retrospective observational study evaluated cardiac arrest patients admitted to the emergency department of a tertiary university hospital. The PaCO₂ and ETCO₂ values at 6, 12, and 24 h after return of spontaneous circulation (ROSC) were obtained from medical records and Pa-ETCO₂ gap was calculated as the difference between PaCO₂ and ETCO₂ at each time point. Multivariate logistic regression analysis was performed to verify the relationship between Pa-ETCO₂ gap and clinical variables. Receiver operating characteristic (ROC) curve analysis was performed to determine the cutoff value of Pa-ETCO₂ for predicting in-hospital mortality.

The final analysis included 58 patients. In univariate analysis, Pa-ETCO₂ gaps were significantly lower in survivors than in non-survivors at 12 h [12.2 (6.5–14.8) vs. 13.9 (12.1–19.6) mmHg, p = 0.040] and 24 h [9.1 (6.3–10.5) vs. 17.1 (13.1–23.2) mmHg, p < 0.001)] after ROSC. In multivariate analysis, Pa-ETCO₂ gap at 24 h after ROSC was related to in-hospital mortality [odds ratio (95% confidence interval): 1.30 (1.07–1.59), p = 0.0101]. In ROC curve analysis, the optimal cut-off value of Pa-ETCO₂ gap at 24 h after ROSC was 10.6 mmHg (area under the curve, 0.843), with 77.8% sensitivity and 85.7% specificity.

The Pa-ETCO₂ gap at 24 h after ROSC was associated with in-hospital mortality in post-cardiac arrest patients.