Safety Study of Inhaled Carbon Monoxide to Treat Acute Respiratory Distress Syndrome (ARDS)

Inclusion Criteria: 1. Patients with sepsis are defined as those with suspected or documented infection: Suspected or proven infection: Sites of infection include thorax, urinary tract, abdomen, skin, sinuses, central venous catheters, and central nervous system All eligible patients meet the new definition of sepsis (suspected or proven infection and a SOFA ≥ 2) as PaO2/FiO2 ratio \< 300 = 2 SOFA points. 2. ARDS is defined when all four of the following criteria are met: * A PaO2/FiO2 ratio ≤ 300 with at least 5 cm H2O positive end-expiratory airway pressure (PEEP) * Bilateral infiltrates consistent with pulmonary edema on frontal chest radiograph * A need for positive pressure ventilation by an endotracheal or tracheal tube * No clinical evidence of left atrial hypertension for bilateral pulmonary infiltrates. 3. ARDS onset is defined as the time the last of criteria 1-4 are met. ARDS must persist through the enrollment time window of 120 hours. 4. Infiltrates considered "consistent with pulmonary edema" include any infiltrates not fully explained by mass, atelectasis, or effusion or opacities known to be chronic (greater than 1 week). Vascular redistribution, indistinct vessels, and indistinct heart borders alone are not considered "consistent with pulmonary edema" and thus would not count as qualifying opacities for this study. Exclusion Criteria: 1. Age less than 18 years 2. Greater than 120 hours since ARDS onset 3. Pregnant or breast-feeding 4. Prisoner 5. Patient, surrogate, or physician not committed to full support (exception: a patient will not be excluded if he/she would receive all supportive care except for attempts at resuscitation from cardiac arrest) 6. No consent/inability to obtain consent 7. Physician refusal to allow enrollment in the trial 8. Moribund patient not expected to survive 24 hours 9. No arterial line/no intent to place an arterial line 10. No intent/unwillingness to follow lung protective ventilation strategy 11. Severe hypoxemia defined as oxygenation saturation (SpO2) \<95 or PaO2 \<80 on FiO2 ≥0.8 12. Hemoglobin \< 7.5 g/dl or hemoglobin \< 8 g/dl and actively bleeding 13. Subjects who are Jehovah's Witnesses or are otherwise unable or unwilling to receive blood transfusions during hospitalization 14. Acute myocardial infarction (MI) or acute coronary syndrome (ACS) within the last 90 days 15. Coronary artery bypass graft (CABG) surgery within 30 days 16. Angina pectoris or use of nitrates with activities of daily living 17. Cardiopulmonary disease classified as New York Heart Association (NYHA) class IV 18. Stroke (ischemic or hemorrhagic) within the prior 3 months 19. Diffuse alveolar hemorrhage from vasculitis 20. Use of high frequency ventilation 21. Participation in other interventional studies involving investigational agents 22. Burns \> 40% total body surface area 23. Use of inhaled pulmonary vasodilator therapy (eg. NO or prostaglandins)