Risk stratification using SpO2/FiO2 and PEEP at initial ARDS diagnosis and after 24 h in patients with moderate or severe ARDS

Luigi Pisani, Jan-Paul Roozeman, Fabienne D. Simonis, Antonio Giangregorio, Sophia M. van der Hoeven, Laura R. Schouten, Janneke Horn, Ary Serpa Neto, Emir Festic, Arjen M. Dondorp, Salvatore Grasso, Lieuwe D. Bos, Marcus J. Schultz, for the MARS consortium

We assessed the potential of risk stratification of ARDS patients using SpO2/FiO2 and positive end-expiratory pressure (PEEP) at ARDS onset and after 24 h. We used data from a prospective observational study in patients admitted to a mixed medical-surgical intensive care unit of a university hospital in the Netherlands. Risk stratification was by cutoffs for SpO2/FiO2 and PEEP. The primary outcome was in-hospital mortality. Patients with moderate or severe ARDS with a length of stay of > 24 h were included in this study. Patients were assigned to four predefined risk groups: group I (SpO2/FiO2 ≥ 190 and PEEP < 10 cm H2O), group II (SpO2/FiO2 ≥ 190 and PEEP ≥ 10 cm), group III (SpO2/FiO2 < 190 and PEEP < 10 cm H2O) and group IV (SpO2/FiO2 < 190 and PEEP ≥ 10 cm H2O). The analysis included 456 patients. SpO2/FiO2 and PaO2/FiO2 had a strong relationship (P < 0.001, R 2 = 0.676) that could be described in a linear regression equation (SpO2/FiO2 = 42.6 + 1.0 * PaO2/FiO2). Risk stratification at initial ARDS diagnosis resulted in groups that had no differences in in-hospital mortality. Risk stratification at 24 h resulted in groups with increasing mortality rates. The association between group assignment at 24 h and outcome was confounded by several factors, including APACHE IV scores, arterial pH and plasma lactate levels, and vasopressor therapy. In this cohort of patients with moderate or severe ARDS, SpO2/FiO2 and PaO2/FiO2 have a strong linear relationship. In contrast to risk stratification at initial ARDS diagnosis, risk stratification using SpO2/FiO2 and PEEP after 24 h resulted in groups with worsening outcomes. Risk stratification using SpO2/FiO2 and PEEP could be practical, especially in resource-limited settings.