Validating Measures of Disease Severity in Acute Respiratory Distress Syndrome

RATIONALE: Quantifying ARDS severity is essential for prognostic enrichment to stratify patients for invasive or higher risk treatments, however, the comparative performance of many ARDS severity measures is unknown.

OBJECTIVE: To validate ARDS severity measures for their ability to predict hospital mortality and an ARDS-specific outcome (defined as death from pulmonary dysfunction or the need for extra-corporeal membrane oxygenation [ECMO] therapy).

METHODS: We compared five individual ARDS severity measures including PaO2/FiO2, oxygenation index, ventilatory ratio, lung compliance, and radiologic assessment of lung edema (RALE); two ARDS composite severity scores including the Murray Lung Injury Score (LIS), and a novel score combining RALE, PaO2/FiO2, and ventilatory ratio; and the APACHE-IV score, using data collected at ARDS onset in patients hospitalized at a single center in 2016 and 2017. Discrimination of hospital mortality and the ARDS specific outcome was evaluated using the area under the receiver operator characteristic curve (AUROC). Measure calibration was also evaluated.

RESULTS: Among 340 ARDS patients, 125 (37%) died during hospitalization and 36 (10.6%) had the ARDS-specific outcome, including one who received ECMO. Among the five individual ARDS severity measures, the RALE score had the highest discrimination of the ARDS-specific outcome (AUROC = 0.67, 95% CI 0.58-0.77), although other ARDS severity measures had similar performance. However, their ability to discriminate overall mortality was low. In contrast, the APACHE-IV score best discriminated overall mortality (AUROC = 0.73, 95% CI 0.67-0.79) but was unable to discriminate the ARDS-specific outcome (AUROC = 0.54, 95% CI 0.44-0.65). Among ARDS composite severity scores, the LIS had an AUROC = 0.67 (95% CI, 0.58-0.75) for the ARDS-specific outcome while the novel score had an AUROC = 0.79 (95% CI 0.61-0.79). Patients grouped by quartile of the novel score had an 6%, 2%, 10%, and 24% rate of the ARDS-specific outcome.

CONCLUSION: While most ARDS severity measures had poor discrimination of hospital mortality, they performed better at predicting death from severe pulmonary dysfunction or ECMO needs. A novel composite score had the highest the discrimination of this outcome.