For patients with ARDS, conservative oxygen strategy is no better, and may be worse, than a more liberal strategy (LOCO2)

Reference

Barrot L, Asfar P, Mauny F, et al, for the LOCO2 Investigators and REVA Research Network. Liberal or conservative oxygen therapy for acute respiratory distress syndrome. N Engl J Med 2020;382(11):999-1008.

Synopsis

Although a target PaO2 of 55 to 80 mm Hg is recommended, this recommendation has not been evaluated in prospective clinical trials. These investigators identified patients who were mechanically ventilated for ARDS for less than 12 hours. All patients had a ratio of PaO2 to fraction of inspired oxygen (FiO2) of no more than 300 mm Hg, positive end-expiratory pressure of at least 5 cm of water, and bilateral opacities on imaging. The mean age of the 205 patients was 63 years, 64% were men, and the mean PaO2:FiO2 ratio was 118 mm Hg (moderate to severe ARDS). Groups were balanced at the start of the study, and analysis was by intention to treat. The patients were randomized to a liberal oxygen therapy group (PaO2 target 90 to 105 mm Hg) or a conservative oxygen therapy group (PaO2 target 55 to 70 mm Hg) for the first 7 days of mechanical ventilation, unless extubated sooner. Blood gasses were measured every 6 hours. Between those measurements the oxygen saturation was maintained at 96% or higher in the liberal oxygen group and between 88% and 92% in the conservative oxygen group. Oxygen exposure was generally consistent with the assigned targets throughout the study period. Although the authors initially hoped to enroll 850 patients, the study was stopped because of safety concerns after only 205 patients had been randomized. At 28 days after trial entry, mortality was numerically but nonsignificantly higher in the conservative oxygen therapy group. This difference became statistically significant after 90 days of follow-up (absolute difference 14%; number needed to treat to harm = 7 for one additional death). Although not statistically significant, there were also more episodes of arrhythmia (23 vs 16), new onset atrial fibrillation (21 vs 13), stroke or seizure (6 vs 1), and mesenteric ischemia (5 vs 0) in the conservative oxygen therapy group.