Slow inclusion

Investigators hypothesized that a relative low SpO2 directed oxygen therapy would reduced the mortality in patients staying longer than 72 hours in ICUs.

In fear of harmful effect of hypoxia, oxygen therapy is commonly used, especially in critically ill patients in intensive care units (ICUs). However, hyperoxia can be harmful too. Examples are myocardial infarction (MI) patients and patients resuscitated to return of spontaneous circulation after cardiac arrest. In Air Versus Oxygen in Myocardial Infarction (AVOID) trial, Meyhoff and colleagues proved hyperoxia caused more cardiac injury in patients with ST-elevation MI but without hypoxia. Kilgannon and colleagues found that arterial hyperoxia following resuscitation from cardiac arrest were associated with increased in-hospital mortality, and a pulse oxygen saturation (SpO2) of 94-98% was recommended.

Recently, Panwar and colleagues found that compared to liberal oxygen strategy (SpO2 ≥96%), conservative oxygen strategy (SpO2 of 88%-92%) was feasible in patients receiving invasive mechanical ventilation. Girardis and colleagues found control oxygen therapy (targeting SpO2 of 94%-98% or PaO2 of 70-100mmHg) resulted lower ICU mortality than conventional oxygen therapy (SpO2 ≥97%) in the randomized clinical trial called Oxygen-ICU. However, the Oxygen-ICU trial was single-centered, early-terminated with only 480 patients included and led to an unplanned interim analysis. In this larger multicenter trial, investigators hypothesized that a relative low SpO2 directed oxygen therapy was safe and would reduced the 28-day mortality in patients staying longer than 72 hours in ICUs.

Inclusion Criteria:

• aged 18 years or older and admitted into ICU, with expected stay in ICU more than 72 hours or longer.

Exclusion Criteria:

• under 18 years old, expected stay in ICU less than 72 hours, unconsented inclusion, ICU readmission, patients with acute exacerbation of chronic obstruction disease, patients with severe acute respiratory distress syndrome (defined as PaO2/FiO2 ≤ 100mmHg and PEEP ≥10cmH2O), decision to withhold life-sustaining treatment, physician forgetting to screen during 12 hours after admission, pregnancy, patients with acute myocardial infarction, paraquat poisoning and patients on extracorporeal membrane oxygenation (ECMO) or planned to be on ECMO.