Impact of HI-NPPV Vs LI-NPPV on Tolerance Among AECOPD Patients

Inclusion Criteria: * AECOPD confirmed by the 2019 criteria of the Global Initiative for Chronic Obstructive Lung Disease (GOLD); * Arterial pH \<7.35 and PaCO2 \>45 mmHg at screening entry; * PaCO2 \>45 mmHg after a 6-hour trial of low-intensity NPPV. Exclusion Criteria: * Age \<18 years * Excessive respiratory secretions with weak cough * Upper airway obstruction * Recent oral, facial, or cranial trauma or surgery * Recent gastric or esophageal surgery * Presence of restrictive ventilatory dysfunction (eg, consolidation or removal of at least one pulmonary lobe, massive pleural effusion, chest wall deformity, continuous strapping with thoracic or abdominal bandage, or severe abdominal distension) * Active upper gastrointestinal bleeding * Cardiac or respiratory arrest * Arterial oxygen tension/fraction of inspired oxygen (PaO2/FiO2) \<100 mmHg * Pneumothorax * Obvious emphysematous bullae confirmed by chest CT scan * Ventricular arrhythmia or myocardial ischemia * Severe hemodynamic instability (mean arterial pressure \<65 mmHg) * Severe metabolic acidosis (pH \<7.20 and bicarbonate \<22 mmol/L) * Refusal to receive NPPV or give informed consent * Prior endotracheal intubation or tracheostomy during the current hospitalization * A do-not-intubate order