Risk stratification using SpO(2)/FiO(2) 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 SpO(2)/FiO(2) 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 SpO(2)/FiO(2) 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 (SpO(2)/FiO(2) ≥ 190 and PEEP < 10 cm H(2)O), group II (SpO(2)/FiO(2) ≥ 190 and PEEP ≥ 10 cm), group III (SpO(2)/FiO(2) < 190 and PEEP < 10 cm H(2)O) and group IV (SpO(2)/FiO(2) < 190 and PEEP ≥ 10 cm H(2)O). RESULTS: The analysis included 456 patients. SpO(2)/FiO(2) and PaO(2)/FiO(2) had a strong relationship (P < 0.001, R (2) = 0.676) that could be described in a linear regression equation (SpO(2)/FiO(2) = 42.6 + 1.0 * PaO(2)/FiO(2)). 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, SpO(2)/FiO(2) and PaO(2)/FiO(2) have a strong linear relationship. In contrast to risk stratification at initial ARDS diagnosis, risk stratification using SpO(2)/FiO(2) and PEEP after 24 h resulted in groups with worsening outcomes. Risk stratification using SpO(2)/FiO(2) and PEEP could be practical, especially in resource-limited settings. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s13613-017-0327-9) contains supplementary material, which is available to authorized users.