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

Background: 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. Methods: 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). Results: The analysis included 456 patients. SpO₂/FiO₂ and PaO₂/FiO₂ had a strong relationship (P < 0.001, R₂ = 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. Conclusions: 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.