Inclusion Criteria:Participants admitted to the RICU with acute hypercapnic respiratory failure requiring NIV support with the following criteria:  RR> 25 breath/minute. Use of accessory muscles of respiration, paradoxical breathing, thoracoabdominal asynchrony.  Hypoxemia evidenced by the following items:  In patient with hypercapnic ARF:  I.Need for oxygen therapy at FIO2> 40% to maintain PaO2 > 60 mmHg or SaO2> 90% II.Blood gas analysis shows pH <7.35 and paCO2> 45 mmHg  -  Exclusion Criteria:Patients with ARF who have any of the following:  I.Indication for emergency endotracheal intubation. II.HR < 50 beat\minute with decreased level of consciousness III.Persistent hemodynamic instability with  Systolic blood pressure <90 mmHg after infusing a bolus of crystalloid solution at a dose of 30 ml / kg. life-threatening arrhythmia. IV.Undrained pneumothorax or Pneumothorax with persistent air leak. V.Extensive facial trauma or burnVI.Refusal to participate. VII.Usual long-term treatment with NIV for chronic disease