Respiratory Drive and Inspiratory Effort in COVID-19 Associated ARDS

Multicenter cohort study in four Italian ICU including adults with moderate and severe CARDS (PaO2/FiO2 \<100 mmHg) at ICU admission. An historical cohort of patients with ARDS from various etiologies used for comparison. Respiratory drive (P0.1), diaphragm electrical activity (EAdi), inspiratory effort derived from EAdi (∆PmusEAdi) and from deflection in airway pressure occluded (ΔPocc) (PmusΔPocc), dynamic transpulmonary driving pressure (ΔPL,dyn, the difference between peak and end-expiratory transpulmonary pressure) measured under assisted ventilation. The main ventilatory pattern variables: * Airway Occlusion Pressure (P0.1): Measurement of the decrease in airway pressure during an end-expiratory occlusion. * Pmus-EAdi-derived (∆Pmus, EAdi): Measurement of the pressure generated by the respiratory muscles during inspiration derived by electrical activity of the diaphragm measurements. * Transpulmonary pressure EAdi-derived (∆Plung,dyn): difference between peak and end-expiratory transpulmonary pressure . * Occlusive Pressure Difference (∆Pocc): Evaluation of the pressure difference between the initial and final airway opening during inspiration. * Pmus-∆Pocc-derived (∆Pmus, ∆Pocc): Measurement of the pressure generated by the respiratory muscles during inspiration derived by ∆Pocc (∆Pocc\*0.75) * Transpulmonary driving pressure ∆Pocc derived (∆Plung, ∆Pocc): calculated as (Peak airway pressure -PEEP) - 2/3 \* ∆Pocc * Diaphragmatic Electrical Activity (EAdi): Recording of the electrical activity of the diaphragm. * Peak EAdi (EAdiPEAK): Determination of the highest recorded value of diaphragmatic electrical activity. * Pressure time product of the trans-diaphragmatic pressure per breath and per minute(PTP/min): the integral of Pmusc-EAdi-derived during inspiration per breath. * Inspiratory Delay (ID): Assessment of the time delay between the start of neural inspiration and the onset of mechanical ventilation. * Neuro-ventilatory Efficiency (NVE): Measurement of the efficiency of the neural drive to the respiratory muscles. * Peak Airway Opening Pressure (PawPEAK): Measurement of the peak pressure in the airway during inspiration. * Inspiratory Pressure-Time Product (PmusEAdi/b): Calculation of the work of breathing by integrating the product of diaphragmatic electrical activity and the change in airway pressure during inspiration. * Tidal Volume (VT): Measurement of the volume of air inspired and expired during each breath. * Respiratory Rate: Calculation of the number of breaths per minute delivered by the mechanical ventilator. * Inspiratory and Expiratory Time (Ti,MECH and Te,MECH): Determination of the duration of mechanical inspiration and expiration. * Inspiratory Duty Cycle (TI/TTOT-neur): Calculation of the ratio of inspiratory time to total respiratory cycle time based on neural inspiration.