A decrease in ARDS mortality was only seen in observational studies from 1984 to 1993. Mortality did not decrease between 1994 (when a consensus definition was published) and 2006, and is lower in RCTs than observational studies.

WHO. Coronavirus disease (COVID-19) advice for the public: when and how to use masks. 2020. https://www.who.int/emergencies/diseases/novelcoronavirus-2019/advice-for-public/when-and-how-to-use-masks (accessed March 17, 2020). 2 State Council, China. Guidelines for the selection and use of different types of masks for preventing new coronavirus infection in different populations 2020 (in Chinese). Feb 5, 2020.

The main characteristics of mechanically ventilated ARDS patients affected with COVID-19, and the adherence to lung-protective ventilation strategies are not well known. We describe characteristics and outcomes of confirmed ARDS in COVID-19 patients managed with invasive mechanical ventilation (MV). Methods: This is a multicenter, prospective, observational study in consecutive, mechanically ventilated patients with ARDS (as defined by the Berlin criteria) affected with with COVID-19 (confirmed SARS-CoV-2 infection in nasal or pharyngeal swab specimens), admitted to a network of 36 Spanish and Andorran intensive care units (ICUs) between March 12 and June 1, 2020. We examined the clinical features, ventilatory management, and clinical outcomes of COVID-19 ARDS patients, and compared some results with other relevant studies in non-COVID-19 ARDS patients. Results: A total of 742 patients were analysed with complete 28-day outcome data: 128 (17.1%) with mild, 331 (44.6%) with moderate, and 283 (38.1%) with severe ARDS. At baseline, defined as the first day on invasive MV, median (IQR) values were: tidal volume 6.9 (6.3-7.8) ml/kg predicted body weight, positive end-expiratory pressure 12 (11-14) cmH 2 O. Values of respiratory system compliance 35 (27-45) ml/cmH 2 O, plateau pressure 25 (22-29) cmH 2 O, and driving pressure 12 (10-16) cmH 2 O were similar to values from non-COVID-19 ARDS patients observed in other studies. Recruitment maneuvers, prone position and neuromuscular blocking agents were used in 79%, 76% and 72% of patients, respectively. The risk of 28-day mortality was lower in mild ARDS [hazard ratio (RR) 0.56 (95% CI 0.33-0.93), p = 0.026] and moderate ARDS [hazard ratio (RR) 0.69 (95% CI 0.47-0.97), p = 0.035] when compared to severe ARDS. The 28-day mortality was similar to other observational studies in non-COVID-19 ARDS patients. Conclusions: In this large series, COVID-19 ARDS patients have features similar to other causes of ARDS, compliance with lung-protective ventilation was high, and the risk of 28-day mortality increased with the degree of ARDS severity.

The early use of noninvasive ventilation averted respiratory failure after extubation and decreased intensive care unit mortality among patients at increased risk. The beneficial effect of noninvasive ventilation in improving survival of hypercapnic patients with chronic respiratory disorders warrants a new prospective clinical trial.

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