Predictive Value of End-Tidal CO₂, Arterial CO₂, CO₂ Gap and Ratio for 30-Day Mortality in Emergency Department...

Background and Objectives: To evaluate the prognostic value of end-tidal carbon dioxide (ETCO₂), arterial carbon dioxide (PaCO₂), their difference (ΔCO₂ = PaCO₂-ETCO₂), and the ETCO₂/PaCO₂ ratio for 30-day mortality in adult patients intubated for acute respiratory failure in the emergency department (ED). Materials and Methods: In this single-center, prospective observational study, we enrolled consecutive adults intubated in the ED who had at least two paired arterial blood gas and capnography measurements within 90 min post-intubation. PaCO₂ and ETCO₂ were recorded at 0, 30, 60, and 90 min, and ΔCO₂ and ETCO₂/PaCO₂ were calculated at each time point. Between-group comparisons, repeated-measures analyses, and logistic regression were used to explore associations, and prognostic performance was assessed using receiver operating characteristic curves. Results: Among 100 patients (36% female); 30- and 90-day mortality were 64% and 70%, respectively. Non-survivors were older, had lower mean arterial pressure after intubation, higher inflammatory and coagulation markers, and more frequent pneumonia and pulmonary embolism. ETCO₂ values were consistently lower in non-survivors at 0, 30, and 60 min, while PaCO₂ was also lower at early time points. ΔCO₂ and the ETCO₂/PaCO₂ ratio did not differ between survivors and non-survivors. Among all CO₂ metrics and time points, only ETCO₂ showed low-to-moderate discrimination for 30-day mortality (area under the curve 0.65-0.70). Conclusions: In ED patients emergently intubated for acute respiratory failure, absolute ETCO₂ values in the early post-intubation period provide modest prognostic information for short-term mortality, whereas ΔCO₂ and ETCO₂/PaCO₂ do not appear to add prognostic value beyond ETCO₂ alone.