Conservative oxygen therapy does not improve survival with a favourable functional outcome at 180 days versus a liberal oxygen therapy in unresponsive adults undergoing mechanical ventilation in the ICU after a cardiac arrest.

The findings, from the Australian-led Low Oxygen Intervention for Cardiac Arrest Injury Limitation (LOGICAL) trial, are consistent with other studies such as the EXACT trial evaluating oxygen use in the out-of-hospital setting after resuscitation from cardiac arrest.

“Available data now suggest that conservative oxygen therapy does not improve patients’ outcomes regardless of the timing of initiation,” the LOGICAL trial said.

The trial, published in the NEJM [link here], randomised 1,840 adult patients from 53 ICUs in Australia, New Zealand, and Ireland to either conservative or liberal oxygen therapy.

The conservative oxygen arm aimed for a SpO₂ upper limit of 95% with Fio₂ decreased to 0.21 versus no SpO₂ upper limit in the liberal oxygen arm and minimum Fio₂ of 0.3. Median hours exposed to SpO₂ ≥97% was 16 in the conservative group versus 37 in the liberal group and the percentage of hours per patient with SpO₂ ≥97% was 21.2% versus 53.0%.

The primary outcome of a favourable functional outcome – an Extended Glasgow Outcome Scale level of 5 to 8 – was achieved by 38.2% of the conservative-oxygen group and 39.7% of the liberal-oxygen group (relative risk, 0.97; 95% CI, 0.87 to 1.09; P = 0.65).

The findings were consistent across pre-specified subgroups including cause of arrest, first monitored rhythm, arrest setting, time from ICU admission to randomisation, and time from return of spontaneous circulation to randomisation.

In a key secondary outcome, 48.0% in the conservative-oxygen group and 49.7% in the liberal-oxygen group were alive at 180 days (adjusted relative risk for death, 0.97).

Other secondary outcomes including median EQ-5D-5L utility score, Montreal Cognitive Assessment-Blind score, median hours of mechanical ventilation, median days in ICU, median hospital stay, and proportion of patients directly discharged from hospital to home were similar in both treatment groups.

The investigators of the trial, auspiced by the Australian and New Zealand Intensive Care Society Clinical Trials Group, said the broad cohort of patients with in-hospital and out-of-hospital cardiac arrests, with few exclusions and run across many sites, increased the generalisability of their findings.

However they noted several trial limitations such as some protocol deviations and the modest between-group separation in daily oxygen-exposure metrics.