Risk factors for the deterioration of oxygenation ratio in ventilated intensive care unit patients: A retrospective cohort study

PurposeThe aim of the study is to determine which factors are associated with the deterioration of Pao2/fraction of inspired oxygen (Fio2) ratio in patients with normal oxygenation at admission and ventilated according to a lung protective ventilation strategy.Materials and MethodsRetrospective cohort study of ventilated (≥3 days) intensive care unit patients with an admission Pao2/Fio2 ratio of 300 mm Hg or higher (n = 105). Patients who developed lung injury (Pao2/Fio2 ratio, <300 mm Hg) on day 7 (n = 37) were compared to those who did not (n = 68), with regard to ventilator settings, gas exchange variables, and lung injury risk factors.ResultsMean ± SD of administered tidal volume was 7.9 ± 1.3 mL/kg. Patients who developed lung injury were older (P = .019), had lower Pao2 (P = .009), higher Paco2 (P = .045), and lower Pao2/Fio2 ratio (P = .002) at admission. Postoperative state (Hazard risk [HR], 5.1) and controlled ventilation mode (HR, 4.3) were identified as independent risk factors. Lung injury-free time was shorter in patients with low initial Pao2/Fio2 ratio (odds ratio, 1.7; P = .039). This effect was not only caused by the baseline difference, as the decrease in Pao2/Fio2 ratio was more pronounced in patients who developed lung injury compared to those who did not (P = .008).ConclusionsLung injury exacerbates during mechanical ventilation. In patients treated with a mean tidal volume of 7.9 mL/kg, controlled ventilation is a major risk factor.