COPD patients hospitalized with mild-to-moderate hypercapnic respiratory failure, defined as arterial pH \[range, e.g., 7.25-7.35\] and PaCO2 \[threshold, e.g., \>45 mmHg and less 60 mmHg\].
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patients with altered mental state, confused, severe agitation or not cooperative were excluded. Also, severe acidosis (pH \<7.25), hemodynamic instability, facial trauma or surgery, cases with severe nasal deformity, immediate indication for invasive ventilation, patient refusal, cases with respiratory rate more than 35 breaths per minute. Respiratory exhaustion, excess use of respiratory accessory muscles, Patients with breathing disorders during sleep as well as cases of upper airway obstruction and patients with history of chronic home ventilation prior admission were another items for exclusion
