FIO2 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 IO 2 is easily obtained at the bedside and from the electronic health record. The F IO 2 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 IO 2 and S pO 2 were consistently more available than was P aO 2 in the electronic health record: ( F IO 2 vs S pO 2 vs P aO 2 : 100 vs 100 vs 72.8% on day 1, and 100 vs 99 vs 21% on day 5). A worsening F IO 2 trajectory was associated with reduced ventilator-free days. From days 2 to 5, every increase in F IO 2 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 S pO 2 /F IO 2 trajectory also provided prognostic information. On days 3 – 5, an increase in S pO 2 /F IO 2 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 S pO 2 /F IO 2 models did not add predictive information compared with models with F IO 2 alone (on day 2: adjusted F IO 2 vs S pO 2 /F IO 2 R2 0.122 vs 0.119; and on day 3: 0.153 vs 0.163). CONCLUSIONS: F IO 2 and S pO 2 /F IO 2 are pragmatic and readily available intermediate prognostic markers in acute hypoxic respiratory failure. The F IO 2 trajectory in the first 5 d of ICU admission provided important prognostic information (ventilator-free days). Although the S pO 2 /F IO 2 trajectory was also associated with ventilator-free days, it did not provide more information than the F IO 2 trajectory alone.