Association between the PaO₂/FiO₂-to-PaCO₂ ratio and mortality in patients with sepsis: a retrospective study with...

Sepsis patients face a high mortality risk. Available prognostic biomarkers have certain limitations. This study explored the prognostic utility of the PaO₂/FiO₂-to-PaCO₂ ratio (PFP) in sepsis.

This study analyzed MIMIC-IV data on 16,546 patients with sepsis admitted to the ICU and categorized into three groups by PFP values calculated from the first arterial blood gas within 24 h of admission. Associations between PFP and mortality were assessed using Kaplan-Meier, Cox regression, and restricted cubic splines (RCS) analyses, and validated using clinical data from a regional hospital. Machine learning was used to develop predictive models for 28- and 90-day mortality, with and without PFP, to evaluate its predictive strength against existing models.

Mortality rates at 28 and 90 days varied significantly across PFP groups (P < 0.001). Cox regression and Kaplan-Meier analyses showed that lower PFP was associated with higher mortality risk (log-rank P < 0.001), Especially among patients receiving mechanical ventilation, which was confirmed by subgroup and sensitivity analyses.RCS analyses demonstrated a nonlinear association between PFP and mortality (cutoff: 4.85). In external validation, lower PFP was linked to higher mortality risk (cutoff: 4.85; log-rank P < 0.001). Machine learning models for 28- and 90-day mortality identified PFP as a significant predictor. Models including PFP improved integrated discrimination improvement (IDI) compared with baseline models (IDI = 0.6%, P = 0.001; IDI = 0.3%, P = 0.002), indicating improved discrimination.

Lower PFP values correlate with higher 28-day and 90-day mortality in septic ICU patients. PFP has modest supplementary prognostic value, mainly in mechanically ventilated patients, not a universal biomarker for all sepsis patients.