To evaluate the accuracy of the arterial oxygen partial pressure/inspired oxygen fraction (PaO₂/FiO₂) ratio in predicting mortality among acute respiratory distress syndrome (ARDS) patients in Vietnam.

A retrospective observational study.

A central hospital in Vietnam.

Adult patients diagnosed with ARDS based on the Berlin definition and admitted to Bach Mai Hospital between August 2015 and August 2023. ARDS severity was converted from descriptive categories to the Berlin score, ranging from 1 (PaO₂/FiO₂>300 mm Hg) to 4 (PaO₂/FiO₂≤100 mm Hg).

All-cause hospital mortality.

Of 345 patients, 67.5% were male, and the median age was 55.0 years (IQR: 39.0–66.0). Hospital mortality was 61.2% (211/345). On the first day of admission, the PaO₂/FiO₂ ratio (areas under the receiver operating characteristic curves (AUROC): 0.585 (95% CI 0.522 to 0.649)) showed limited predictive ability for hospital mortality. Incorporating the PaO₂/FiO₂ ratio into the Berlin score did not substantially improve accuracy (AUROC: 0.578 (95% CI 0.516 to 0.641)). Both measures were less accurate than Sequential Organ Failure Assessment (SOFA) (AUROC: 0.650 (95% CI 0.590 to 0.711)), Acute Physiology and Chronic Health Evaluation II (APACHE II) (AUROC: 0.685 (95% CI 0.628 to 0.742)) and Confusion, Urea >7 mmol/L (20 mg/dL), Respiratory rate ≥30 breaths/min, Blood pressure (systolic 2/FiO₂ values (adjusted OR, AOR: 0.988 (95% CI 0.979 to 0.996)) were independently associated with lower mortality risk, while higher Berlin (AOR: 2.477 (95% CI 1.190 to 5.156)), SOFA (AOR: 1.278 (95% CI 1.102 to 1.482)), APACHE II (AOR: 1.236 (95% CI 1.108 to 1.379)) and CURB-65 (AOR: 7.142 (95% CI 2.581 to 19.763)) scores were associated with increased mortality risk.

In this study of ARDS patients in Vietnam, the PaO₂/FiO₂ ratio demonstrated limited discriminatory ability for hospital mortality, and incorporating it into the Berlin score did not meaningfully improve performance. While less accurate than SOFA, APACHE II and CURB-65 scores, the PaO₂/FiO₂ ratio and Berlin score remained independently associated with mortality risk. These findings should be interpreted cautiously, given the retrospective design, single-centre setting and potential selection bias; further validation in larger, multicentre studies is warranted.