In mechanically ventilated adults receiving supplemental oxygen in the ICU, conservative oxygen therapy did not lead to meaningful reductions in all-cause mortality at 90 days, according to new U.K. research. The UK-ROX Randomized Clinical Trial included 16,500 mechanically ventilated patients across 97 ICUs between 2021 and 2024. Patients were randomized to conservative oxygen therapy, receiving the lowest fraction of inspired oxygen possible to maintain their Spo2 at 90%, or to usual oxygen therapy, which was administered at the discretion of the treating clinician. The conservative oxygen therapy group had 29% lower supplemental oxygen exposure compared with the usual oxygen therapy group. All-cause mortality at 90 days – the primary outcome – was 35.4% in the conservative oxygen therapy group and 34.9% in the usual oxygen therapy group. No significant differences were seen in secondary outcomes including length of stay in ICU or hospital, days alive and free from organ support at 30 days, or mortality at other time points.