Risk stratification of acute respiratory distress syndrome using a PaO2: Fio2 threshold of 150 mmHg: A retrospective analysis from an Indian intensive care unit

Background: Whether a Pa-O2: F-O2 ratio of 150 mmHg could be used to classify patients with acute respiratory distress syndrome (ARDS) as severe or non-severe is unknown. Herein, we study whether Pa-O2: Fi(O2) < 150 mmHg could be used as a risk stratification and prediction tool for mortality in patients with ARDS. Methods: Patients with ARDS (Pa-O2: Fi(O2) ratio <= 300 mmHg) were categorized as nonsevere ARDS (150 <= Pa-O2: Fi(O2) ratio <= 300 mmHg) and severe ARDS (Pa-O2: Fi(O2) ratio <150 mmHg). We compared the physiological characteristics, ventilatory parameters, and mortality between the two groups. Further, we subcategorized those with severe ARDS as very severe (Pa-O2: Fi(O2) ratio <= 100 mmHg) or severe ARDS (100<Pa-O2: Fi(O2) ratio <150 mmHg). We also compared the performance of this cut off value with the Berlin criteria using the receiver operating characteristic curve. Results: Four hundred and sixty (256, non-severe ARDS; 204, severe ARDS) patients (mean standard deviation age, 40 (17) years, 55% males) with ARDS were included. Patients with severe ARDS had significantly lower baseline pH and higher Pa-CO2. Patients with severe ARDS also had higher plateau pressure, peak airway pressure, applied positive end-expiratory positive pressure. The odds ratio (95% confidence interval [CI]) of mortality in those with severe ARDS was 1.6 (95% CI, 1.1-2.4). Although the AUC for both the revised and Berlin models was low, on a multivariate logistic regression analysis, after adjusting for age, gender, sequential organ failure assessment score, driving pressure, and mechanical power, Pa-O2: Fi(O2) ratio of 150 mmHg remained an independent risk for mortality. Conclusions: The Pa-O2: Fi(O2) ratio threshold of 150 mmHg may be used to identify severe ARDS. However, used alone a Pa-O2: Fi(O2) threshold of 150 mmHg has poor sensitivity in predicting mortality. Due to the small sample, the results of our study should be confirmed in a larger multicentric study.