F_io2 trajectory as a pragmatic intermediate marker in acute hypoxic respiratory failure

BACKGROUND: Several markers of oxygenation are used as prognostic markers in acute hypoxemic respiratory failure. Real-world use is limited by the need for invasive measurements and unreliable availability in the electronic health record. A pragmatic, reliable, and accurate marker of acute hypoxemic respiratory failure is needed to facilitate epidemiologic studies, clinical trials, and shared decision-making with patients. F_IO2 is easily obtained at the bedside and from the electronic health record. The F_IO2 trajectory may be a valuable marker of recovery in patients with acute hypoxemic respiratory failure. METHODS: This was a historical cohort study of adult subjects admitted to an ICU with acute hypoxemic respiratory failure secondary to community-acquired pneumonia and/or ARDS. RESULTS: Our study included 2,670 subjects. F_IO2 and S_pO2 were consistently more available than was P_aO2 in the electronic health record: (F_IO2 vs S_pO2 vs P_aO2: 100 vs 100 vs 72.8% on day 1, and 100 vs 99 vs 21% on day 5). A worsening F_IO2 trajectory was associated with reduced ventilator-free days. From days 2 to 5, every increase in F_IO2 by 10% from the previous day was associated with fewer ventilator-free days (on day 2: adjusted mean –1.25 [95% CI –1.45 to –1.05] d, P < .001). The S_pO2 =F_IO2 trajectory also provided prognostic information. On days 3 – 5, an increase in S_pO2 =F_IO2 from the previous day was associated with increased ventilator-free days (on day 3: adjusted mean 2.09 (95% CI 1.44–2.74) d; P < .001). S_pO2 =F_IO2 models did not add predictive information compared with models with F_IO2 alone (on day 2: adjusted F_IO2 vs S_pO2 =F_IO2 R² 0.122 vs 0.119; and on day 3: 0.153 vs 0.163). CONCLUSIONS: F_IO2 and S_pO2 =F_IO2 are pragmatic and readily available intermediate prognostic markers in acute hypoxic respiratory failure. The F_IO2 trajectory in the first 5 d of ICU admission provided important prognostic information (ventilator-free days). Although the S_pO2 =F_IO2 trajectory was also associated with ventilator-free days, it did not provide more information than the F_IO2 trajectory alone.