1. Assessment of benefits of HVNI in management of obesity hypoventilation syndrome complicated with acute hypercapnic respiratory failure.
2. Compare the value, safety and effectiveness of HVNI and NIV in patients with obesity hypoventilation syndrome complicated with acute hypercapnic respiratory failure.

Obesity has become a worldwide health concern. Moreover, obese patients often present comorbidities, such as obstructive apnea syndrome or obesity hypoventilation syndrome. Atelectasis formation is increased in obese patients, because of the negative effects of thoracic wall weight and abdominal fat mass on pulmonary compliance, leading to decreased functional residual capacity (FRC) and arterial oxygenation. The repetitive occurrence of rapid eye movement (REM) sleep, hypoventilation or obstructive sleep apnea with long-lasting apnea and hypopnea induces a secondary depression of respiratory drive with daytime hypercapnia, leading to obesity hypoventilation syndrome. Obesity hypoventilation syndrome is defined as a combination of obesity (body mass index [BMI] ≥ 30 kg/m2), daytime hypercapnia (PaCO2 > 45 mm Hg), and disordered breathing during sleep.

Obese patients represent a specific population in the intensive care unit. Obese patients can be admitted in a critical care setting for de novo acute respiratory failure, 'acute-on-chronic' respiratory failure with an underlying disease, such as an obesity hypoventilation syndrome, or in the perioperative period. The main challenges for ICU clinicians are to take into account the pulmonary pathophysiological specificities of the obese patient to optimize airway management and non-invasive or invasive mechanical ventilation.

Noninvasive ventilation (NIV) has revolutionized the management of acute respiratory failure. NIV obviates endotracheal intubation and thus decreases the risk of ventilator-induced pneumonia, shortens ICU stay, and decreases the overall cost of hospitalization.

Oxygen delivery through high flow nasal cannula (HFNC) has used for the treatment of certain hypoxic situations like bronchiolitis in neonate. HFNC acts as non-invasive ventilator by reducing airway resistance and improving CO2 clearance by providing positive end-expiratory pressure (PEEP). Therefore, it is feasible to employ NFC in the case of obstructive pulmonary diseases. Since HFNC can open the airway by inducing stenting effects, it supplies more effective oxygenation with stable fraction of inspired oxygen (FIO2) in the range of 21 to 100% and a flow rate of up to 60 L/min.

High velocity nasal insufflation (HVNI), a form of HFNC that utilizes a small-bore nasal cannula to generate higher velocities of gas delivery than its counterparts using large bore HFNC, has the ability to accomplish complete purge of extra thoracic dead space at flow rates of 35 liters/min and may be able to provide ventilatory support in patients with acute hypercapnic respiratory failure in addition to oxygenation support.

Inclusion Criteria:

1. Age >18 years.
2. Obesity hypoventilation syndrome with acute hypercapnic respiratory failure. A) Body mass index [BMI] ≥ 30 kg/m2. B) Daytime hypercapnia (PaCO2 > 45 mm Hg) C) PH < 7.35 D) Arterial oxygen saturation (SaO2) <90%

Exclusion Criteria:

1. Age <18 years.
2. Pulmonary infiltrates suggesting pulmonary edema, pneumonia, active tuberculosis, or its sequelae.
3. Patients with gas exchange alterations due to other conditions, such as bronchiectasis, fibrosis of the pleural space (fibrothorax), neuromuscular disease and chronic obstructive pulmonary disease (COPD)
4. Pregnancy.
5. Contraindications for positive-airway pressure devices.