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 (n=70) will be divided into three sub-cohorts. Sub-Cohort 1 (n=60) will be monitored with EIT before, during, and after the administration of iNO (OFF-ON-OFF). Sub-Cohort 2 (n=10) will be monitored with EIT before and during the administration of iNO (OFF-ON) in the supine and in the prone position, and with DECT in the supine and in the prone position (without iNO). Sub-Cohort 3 (n=10) will be a subset of Cohort 1 and will be monitored with DECT before and during the administration of iNO, in addition to EIT monitoring before, during and after iNO administration (OFF-ON-OFF). 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 measure the topographic perfusion response to prone position, applied alone and in combination with iNO): \- Sub-Cohort 2 (n=10) will be monitored with EIT before and after 15 minutes receiving 20ppm iNO in an OFF-ON fashion, both in the supine and in the prone position. A second EIT measurement off iNO will not be obtained to minimize the total dose of hypertonic saline solution. The subjects will be transported to the computed tomography (CT) room, and DECT will be performed first in the supine position. A second DECT will be obtained after 30 minutes in the prone position. No iNO will be given during DECT. Methods to answer question 3 (To compare changes of regional lung perfusion due to iNO detected by EIT against the changes detected by gold standard DECT): \- 10 subjects in Sub-Cohort 1 will receive DECT in addition to EIT monitoring in the supine position. DECT will be obtained before the iNO delivery. Then, the iNO delivery will start, and after 15 minutes, DECT will be repeated. Methods to answer question 4 (to define correlations between EIT-derived perfusion changes during an iNO challenge and clinical characteristics and outcomes. ): \- The investigators will explore the vascular response measured by EIT from all 70 subjects and categorize subjects accordingly. The investigators plan to apply EIT patterns as an image marker and use them in conjunction with other markers (demographical, radiological, clinical, biochemical, and inflammatory) to identify ARDS severity. 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.