Noninvasive Ventilation Facemasks Favoring Carbon Dioxide Washout

Inclusion Criteria: Acute respiratory failure with * PaCO2 ≥ 45 mmHg; * Arterial pH \< 7.35; * Signed written informed consent Exclusion Criteria: * Respiratory rate \< 12 bpm; * Immediate need for intubation; * Haemodynamic instability (Systolic blood pressure \<90 mmHg or mean arterial pressure \<65 mmHg) and/or lactic acidosis (lactate \>5 mmol/L) and/or clinically diagnosed shock; * Metabolic Acidosis; * Recent head surgery or anatomy that prevent the application of facemasks; * Any contraindications to oesophageal balloon insertion and/or electrical impedance tomography (EIT) belt placement. * Any contraindications to facemask noninvasive ventilation.