Respiratory Mechanics and Gas Exchange in Acute Respiratory Distress Syndrome Associated with COVID-19

Aim. To compare respiratory mechanics and gas exchange in patients with acute respiratory distress syndrome (ARDS) with and without COVID-19.

Material and methods. We examined 96 patients, who were divided into two groups. The main group included 48 patients with COVID-19-associated ARDS. The control group included 48 patients with ARDS not associated with COVID-19. Most characteristic patients were selected for the following baseline parameters: age, sex, SAPS II score, disease severity, plateau pressure (Pplateau), oxygenation index (PaO₂/FiO₂), and arterial-alveolar oxygen gradient (A-aO₂). Respiratory mechanics and gas exchange parameters assessed immediately after ARDS diagnosis and on days 1, 3 and 7 of treatment included arterial oxygen (PaO₂) and carbon dioxide (PaCO₂) pressure, tidal volume (Vt), respiratory rate (RR), respiratory minute volume (RMV), positive end expiratory pressure (PEEP), and Pplateau.

Results. Patients in the main group had higher Vt (9.7 vs. 5.1 ml/kg, P<0.001), RR (38 vs. 30 min-1, P<0.001), and RMV (27.7 vs. 10.5 l/min, P<0.001). Control group patients showed hypercapnia (PaCO₂ 43 vs. 38 mmHg, P<0.001), lower respiratory compliance (30 vs. 48 ml/cm H₂O, P<0.001) and ventilation ratio (VR) (1.5 vs. 2.0, P<0.01). Lower PEEP values were required for patients in the main group. However, despite the higher rate of tracheal intubation in the control group (50% vs 16.7%) in the initial period of intensive care, the proportion of patients receiving invasive lung ventilation was significantly higher in the main group (33.3% vs.14.6%) by day 7.

Conclusion. The initial phase (the first 7 days) of ARDS associated with COVID-19 is characterized by higher values of Vt, RR and RMV, as well as lung compliance vs «typical» ARDS with almost identical PaO₂/FiO₂ values.

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