1. Mental obtundation at ICU admission 2. Contraindications or unwillingness to NIV 3. Requiring mechanical ventilation at ICU admission 4. Pre-enrollment diagnosis of chronic renal failure (CRF) or stage 1 Acute Kidney Injury (AKI) as per Kidney Disease Improving Global Outcomes (KDIGO) guidelines 5. Presence of hemoglobinopathies 6. Shock at presentation (mean arterial pressure <60) 7. History of G6PD deficiency or baseline methemoglobin >3% 8. Presence of baseline pulmonary artery hypertension 9. Pregnancy or breastfeeding

1. Mental obtundation at ICU admission 2. Contraindications or unwillingness to NIV 3. Requiring mechanical ventilation at ICU admission 4. Pre-enrollment diagnosis of chronic renal failure (CRF) or stage 1 Acute Kidney Injury (AKI) as per Kidney Disease Improving Global Outcomes (KDIGO) guidelines 5. Presence of hemoglobinopathies 6. Shock at presentation (mean arterial pressure <60) 7. History of G6PD deficiency or baseline methemoglobin >3% 8. Presence of baseline pulmonary artery hypertension 9. Pregnancy or breastfeeding