Baseline Characteristics according to NIV initiation conditions.

Chronic = Chronic Respiratory Failure; Acute: Acute Respiratory Failure; I.C.U: Intensive Care Unit; BMI: Body Mass Index; n of ABG with O2: number of arterial blood gases realized with additional O2; VC: Vital Capacity expressed as percentage of predicted value; FEV1/VC: Forced Expiratory Volume in one second/Vital Capacity ratio; Heart failure included (ischemic, hypertrophic or dilated); COPD: Chronic Obstructive Pulmonary Disease; OSAS: Obstructive Sleep Apnea Syndrome; CEI: Angiotensin Converting Enzyme Inhhnibitors; ARBs: Angiotensin II Receptor Blockers.*#: represent significant difference between pairwise comparisons.