Respiratory physiology of COVID-19-induced respiratory failure compared to ARDS of other etiologies

BackgroundWhether respiratory physiology of COVID-19-induced respiratory failure is different from acute respiratory distress syndrome (ARDS) of other etiologies is unclear. We conducted a single-center study to describe respiratory mechanics and response to positive end-expiratory pressure (PEEP) in COVID-19 ARDS and to compare COVID-19 patients to matched-control subjects with ARDS from other causes.MethodsThirty consecutive COVID-19 patients admitted to an intensive care unit in Rome, Italy, and fulfilling moderate-to-severe ARDS criteria were enrolled within 24h from endotracheal intubation. Gas exchange, respiratory mechanics, and ventilatory ratio were measured at PEEP of 15 and 5cmH(2)O. A single-breath derecruitment maneuver was performed to assess recruitability. After 1:1 matching based on PaO2/FiO(2), FiO(2), PEEP, and tidal volume, COVID-19 patients were compared to subjects affected by ARDS of other etiologies who underwent the same procedures in a previous study.ResultsThirty COVID-19 patients were successfully matched with 30 ARDS from other etiologies. At low PEEP, median [25th-75th percentiles] PaO2/FiO(2) in the two groups was 119mmHg [101-142] and 116mmHg [87-154]. Average compliance (41ml/cmH(2)O [32-52] vs. 36ml/cmH(2)O [27-42], p =0.045) and ventilatory ratio (2.1 [1.7-2.3] vs. 1.6 [1.4-2.1], p =0.032) were slightly higher in COVID-19 patients. Inter-individual variability (ratio of standard deviation to mean) of compliance was 36% in COVID-19 patients and 31% in other ARDS. In COVID-19 patients, PaO2/FiO(2) was linearly correlated with respiratory system compliance (r =0.52 p =0.003). High PEEP improved PaO2/FiO(2) in both cohorts, but more remarkably in COVID-19 patients (p =0.005). Recruitability was not different between cohorts (p =0.39) and was highly inter-individually variable (72% in COVID-19 patients and 64% in ARDS from other causes). In COVID-19 patients, recruitability was independent from oxygenation and respiratory mechanics changes due to PEEP.ConclusionsEarly after establishment of mechanical ventilation, COVID-19 patients follow ARDS physiology, with compliance reduction related to the degree of hypoxemia, and inter-individually variable respiratory mechanics and recruitability. Physiological differences between ARDS from COVID-19 and other causes appear small.