To evaluate whether early application of nasal high flow oxygen therapy after extubation can reduce the incidence of postoperative hypoxemia (defined as a PaO2/FiO2 ratio <300) after abdominal surgery in patients with intermediate to high risk of postoperative pulmonary complications.

Postoperative hypoxemia complicates between 30 to 50% of patients after abdominal surgery. Loss of functioning alveolar units and development of atelectasis after abdominal surgery have been recognized as the underlying mechanisms responsible for postoperative hypoxemia. Supplemental Oxygen administration is therefore widely recommended after extubation in the postoperative period, especially in patients with high risk of postoperative respiratory complications. Although oxygen therapy is effective in preventing the vast majority of severe postoperative hypoxemia after extubation in surgical patients, respiratory failure may occur, thus requiring endotracheal intubation and mechanical ventilation or therapeutic use of non-invasive positive pressure ventilation (NPPV). In patients with postoperative hypoxemia (defined as patients with a PaO2/FiO2 ratio <300), application of NPPV was found to decrease the incidence of endotracheal intubation after abdominal surgery. Nevertheless, use of NPPV in the postoperative period is responsible for organizational constraints and increases healthcare utilization.

Nasal high flow cannula (NHFC) has been described as an attractive and well-tolerated method of non-invasive oxygen delivery. Previous studies have shown that NHFC generates a low level of positive airway pressure, increases end-expiratory lung volume and reduces airway resistance, thus contributing to a reduction in work of breathing. To date, however, no clinical trials have compared NHFC to standard oxygen therapy in the prevention of postoperative hypoxemia after abdominal surgery in patients with intermediate to high risk of postoperative pulmonary complications.

The primary objective of the study is to compare: 1- Standard oxygen therapy; 2- Nasal high flow oxygen therapy after extubation in patients with intermediate to high risk of postoperative pulmonary complications after abdominal surgery.

Our hypothesis is that, compared with standard oxygen therapy, early application of nasal high flow oxygen therapy can reduce the need for postoperative NPPV for postoperative hypoxemia (defined as PaO2/FiO2 ratio <300).

Inclusion Criteria:

• Planned or unplanned surgical procedures
• Abdominal or abdominal and thoracic surgery
• Expected duration ≥2 hours
• ARISCAT score ≥26 points

Exclusion Criteria:

• Age <18 years
• Body mass index >35 kg/m2
• Sleep apnea syndrome
• Patient refusal
• Pregnancy and/or lactation