In patients with acute respiratory distress syndrome (ARDS), the National Heart, Lung, and Blood Institute ARDS Clinical Trials Network recommends a target partial pressure of arterial oxygen (Pao) between 55 and 80 mm Hg. Prospective validation of this range in patients with ARDS is lacking. We hypothesized that targeting the lower limit of this range would improve outcomes in patients with ARDS.
In this multicenter, randomized trial, we assigned patients with ARDS to receive either conservative oxygen therapy (target Pao, 55 to 70 mm Hg; oxygen saturation as measured by pulse oximetry [Spo], 88 to 92%) or liberal oxygen therapy (target Pao, 90 to 105 mm Hg; Spo, ≥96%) for 7 days. The same mechanical-ventilation strategies were used in both groups. The primary outcome was death from any cause at 28 days.
After the enrollment of 205 patients, the trial was prematurely stopped by the data and safety monitoring board because of safety concerns and a low likelihood of a significant difference between the two groups in the primary outcome. Four patients who did not meet the eligibility criteria were excluded. At day 28, a total of 34 of 99 patients (34.3%) in the conservative-oxygen group and 27 of 102 patients (26.5%) in the liberal-oxygen group had died (difference, 7.8 percentage points; 95% confidence interval [CI], -4.8 to 20.6). At day 90, 44.4% of the patients in the conservative-oxygen group and 30.4% of the patients in the liberal-oxygen group had died (difference, 14.0 percentage points; 95% CI, 0.7 to 27.2). Five mesenteric ischemic events occurred in the conservative-oxygen group.
Among patients with ARDS, early exposure to a conservative-oxygenation strategy with a Pao between 55 and 70 mm Hg did not increase survival at 28 days. (Funded by the French Ministry of Health; LOCO number, NCT02713451.).

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