Open Lung Strategy, Gas Distribution and Right Heart Function in ARDS Patients

A recent large observational study published on JAMA showed that Acute Respiratory Distress Syndrome (ARDS) is associated with high mortality and developed in 10.4% of 29,144 patients admitted to the intensive care unit from 50 countries across 5 continents. Mechanical ventilation is the cornerstone for lung treatment during ARDS. Lung protective ventilation improved ARDS outcome significantly. However, it is still unclear what method should be used to select levels of positive end-expiratory pressure (PEEP). In the current study proposal, the investigators hypothesized that, when ARDS lungs are recruitable, a lung recruitment maneuver (LRM) and PEEP titration ("PEEPLRM") improve ventilation/perfusion matching and decreased right heart workload when compared to the actual standard of care PEEP selection based on low PEEP/high FiO2 table ("PEEPARDSnet"). The investigators will test this hypothesis in an interventional crossover study. 50 patients with ARDS will be enrolled in a physiological and lung and heart imaging study. The protocol is divided in the following phases: A) "PEEPARDSnet": setting PEEP according to the ARDSnet table (low PEEP/ high FiO2) B) Recruitability assessment sequence: P-V curve tool (Hamilton ventilator): evaluate patient recruitability, among three criteria, two must be positive to consider a subject recruitable: (1) Presence of a lower inflection point (2) Linear compliance measured more than 2 times higher than the dynamic compliance (3) Increase in volume of more than 300mL during the descendant limb of the PV curve at a same given pressure (20 cmH2O)(Hysteresis property). C)"PEEPLRM": LRM plus PEEP decremental trial guided by best compliance. Lung and heart response to "PEEPLRM": we will compare the driving pressure (DP) value (DP = Plateau pressure - PEEP) and transthoracic echocardiography (TTE) with the values at PEEPARDSnet. In the advent of an increased DP and/or new onset of abnormal values at the TTE, we will resume the PEEPARDSnet settings during the 48h follow-up phase. Before and after the lung recruitment maneuver and decremental PEEP trial, we will collect: 1. Respiratory system mechanics 2. Lung volumes 3. Gas exchange 4. Hemodynamic parameters 5. Electrical Impedance Tomography (EIT) ventilation and perfusion data 6. Transthoracic echocardiographic indices of RH function Follow-up phase: In 24 and 48 hours, if the subject did not present a negative response to "PEEPLRM" as described above , we will repeat the recruitment maneuver and the decremental PEEP trial and and we will collect: 1. Respiratory system mechanics (i.e. driving pressure) 2. Lung volumes 3. Gas exchange 4. Hemodynamic parameters 5. EIT ventilation and perfusion data 6. Transthoracic echocardiographic indices of RH function before and after the aforementioned intervention.