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