Dead Space and Inhaled Nitric Oxide in Pediatric Acute Respiratory Distress Syndrome

Inclusion Criteria: * Age \>37 weeks corrected gestational age to 21 years, including adults lacking the capacity to consent. * Within 72 hours of the start of invasive mechanical ventilation and meet the criteria for pediatric ARDS (new infiltrate on chest imaging and a known ARDS risk factor within 7 days of the onset of hypoxemia) and either meet criteria for moderate or severe pediatric ARDS between 4-72 hours of IMV (OI ≥ 8 or OSI ≥ 7.5) OR have an OI ≥ 20 or an OSI ≥ 14 x 15 minutes between 0-4 hours of IMV. * Subgroup of children eligible for longituduinal Blood Collection: Children with severe PARDS (OI ≥ 16 or an OSI ≥ 12 between 4-72 hours of IMV) or those with an OI ≥ 20 or an OSI ≥ 14 for 15 minutes between 0-4 hours of IMV will be eligible for collection of longitudinal plasma samples. Exclusion Criteria: * Non-conventional invasive mechanical ventilation (i.e. High Frequency Oscillatory Ventilation, Airway Pressure Release Ventilation) at the time of ICU admission * ECMO or iNO (or other inhaled pulmonary vasodilator therapy) at the time of ICU admission * Significant lower airways obstruction (examination of ventilator and capnography waveforms by site study or medical team) * Air leak \>20% (endotracheal tube, tracheostomy tube, or thoracostomy tube) * Home Invasive Mechanical Ventilation * Cyanotic Congenital Heart Disease * Previous enrollment in the DiNO study * Do not resuscitate order at the time of pediatric ARDS diagnosis. * Blood gas not obtained prior to initiation of ECMO, iNO, or non-conventional ventilation.