IGH-FLOW NASAL OXYGEN (HFNO) therapy delivers low-level, flow-dependent positive airway pressure and may be tolerated better than continuous positive airway pressure (CPAP) or noninvasive bi-level positive airway pressure (BiPAP) and enhance washout of nasopharyngeal deadspace, thus improving oxygenation. 1,2 The apparatus is composed of an air/oxygen blender, an active heated humidifier, a single heated circuit, and a nasal cannula. At the air/ oxygen blender, the inspiratory fraction of oxygen (FIO2) is set from 0.21 to 1.0 at a flow of up to 60 L/min. The gas is heated and humidified with the active humidifier and delivered through the heated circuit. Theoretically, HFNO has a number of advantages over other respiratory support systems, including conventional nasal cannulae, face masks, or CPAP/BiPAP. First, because gas generally is warmed to 371C and completely humidified in HFNO circuits, mucociliary function remains intact and patients report minimal discomfort. Mechanical splinting of the nasopharynx prevents supraglottic collapse and decreases nasopharyngeal resistance, and at 60 L/min HFNO can generate positive end-expiratory pressure (PEEP) of 4 to 7.4 cmH2O, which may counterbalance auto-PEEP and reduce the work of breathing. 3,4 HFNO therapy has been gaining attention as an innovative form of respiratory support in various clinical settings. It is being used increasingly in critically ill patients and gaining favor in the perioperative period. HFNO has been used for multiple indications, including hypoxemic respiratory failure and cardiogenic pulmonary edema, to counterbalance autoPEEP in patients with chronic obstructive airway disease and as prophylactic therapy or treatment of respiratory failure after surgery and extubation. 5 It has been shown to be both safe and noninferior to conventional CPAP in providing prophylactic support to very preterm neonates after extubation. 6 In this same study, the incidence of nasal trauma also was significantly lower in the nasal cannulae group than in the CPAP group. Little clinical experience has been reported on the use of HFNO in the cardiothoracic surgical patient population. Patients undergoing cardiothoracic surgery are at significant risk of postoperative pulmonary complications, and these complications may increase morbidity and mortality and lead to prolonged intensive care unit and hospital length of stay. 7 The incidence of pulmonary complications ranges from 8% to 79% after cardiac surgery and has been reported to be as high as 50% after lung resection surgery. 8 Postoperative pulmonary complications manifest early as arterial hypoxemia, during the later course as pneumonia, and in rare cases also as acute respiratory distress syndrome. 9 The pathogenesis of