Vascular ARDS Recruitment After Inhaled Nitric Oxide

The investigators will screen patients with ARDS diagnosis daily at MGH intensive care units and work in the consenting process with the ICU team and surrogates. The enrollment period will be limited to the time subjects will undergo the study procedures. Subjects will exit the study as soon as the study procedures are completed. No further procedures are planned; therefore, subjects will not be asked to return to the hospital exclusively for research-related purposes. The enrolled subjects will be divided into two cohorts. Cohort 1 (n=60) will be monitored with EIT before, during, and after the administration of iNO. Cohort 2 (n=10) will be monitored with EIT and DECT before and during the administration of iNO. Methods to answer question 1 (To measure the topographic perfusion response to an iNO challenge with EIT): \- The EIT monitoring will be composed of ventilation and perfusion distributions. First, the ventilation is recorded; at this point, no additional maneuver is needed; the subjects need to wear the electrode belt connected to the device, and their ventilation will be recorded. Secondly, for the perfusion distribution, after a pause in the ventilation, EIT measures the distribution of blood perfusion in the lungs during the injection of a 10 mL bolus of 11.7% hypertonic saline solution through a central venous catheter. Cohort 1 (n=60) will receive 20ppm of iNO for 15 minutes. Cohort 1 will be monitored with EIT before, during, and after the iNO delivery in an OFF-ON-OFF fashion. Methods to answer question 2 (To compare EIT measurements against the gold standard DECT): \- Cohort 2 (n=10) will be monitored with EIT and DECT. They will receive 20ppm of iNO for 15 minutes. The subjects will be transported to the computed tomography (CT) room, and the first DECT (DECT OFF) will be performed before the iNO delivery. After the DECT OFF, the EIT belt will be placed, and ventilation/perfusion will be measured before the iNO delivery (EIT OFF). Then, the iNO delivery will start, and after 15 minutes, the EIT ON will be recorded. The EIT belts will be removed, and the second DECT (DECT ON) will be performed. Of note, the EIT belt needs to be removed before the DECT acquisitions because the electrodes generate artifacts that would compromise the image quality. Methods to answer question 3 (To determine ARDS phenotypes based on regional perfusion imaging): \- The investigators will explore the vascular response measured by EIT and categorize subjects accordingly. The investigators plan to apply EIT patterns as an image marker and combine them with other markers (demographical, radiological, clinical, biochemical, and inflammatory) to identify ARDS sub-phenotypes. Finally, * Blood MetHb levels will be continuously monitored before, during, and after each iNO administration of the day. At the end of each iNO administration, MetHb will continue to be monitored until values return to the level recorded before the current treatment and * The NO, nitrogen dioxide (NO2) will be continuously monitored by INOmax DSIR (Mallinckrodt) deliver system.