Influence of FreeO2 on Percentage of Time Within Oxygen Saturation Target Using Noninvasive Ventilation (NIV) and Continuous Positive Airway Pressure (CPAP) for Patients Admitted for AECOPD or Bariatric Surgery

Inclusion Criteria (AECOPD): * Respiratory acidosis (pH \<= 7.35 and PaCO2 \> 45 mmHg), with or without NIV (last blood gas available during hospitalization) * Oxygen therapy and/or SpO2 \<90% room air (FiO2 \<= 50% or nasal cannula \<= 7 L/min to maintain SpO2 90%) * High flow nasal cannula with flow \<= 30 L/min Inclusion Criteria (Bariatric surgery post-op): * Patients using CPAP before the surgery (obstructive sleep apnea documented). * Patients with obesity hypoventilation syndrome in addition to obstructive sleep apnea can be included. Exclusion Criteria: * Age \< 18 * Pregnancy * Respiratory distress or other clinical situation requiring continuous NIV or CPAP * Glasgow \< 12 or agitation/delirium/dementia (limiting NIV) * Any contraindication to NIV (state requiring immediate endotracheal intubation, pneumothorax, recent esophagus surgery) * Hemodynamic instability (at the beginning of the study) (increasing doses of vasopressors or inotropes) * Refusal to consent to the study 5 patient with AECOPD and 5 patient with bariatric surgery will be included.