High Flow Oxygen Therapy – Risks and Rewards

Abstract

Introduction High Flow Oxygen Therapy via Nasal Cannula (HFNC) has documented advantages over conventional oxygen therapy (COT). It’s been noted to improve the survival rate among patients with acute hypoxemic respiratory failure, and potentially reduce the incidence of more invasive care. Adjustable oxygen concentration and higher flows that match the inspiratory demand of the patient with respiratory distress result in less entrainment of room air, which dilutes the fraction of inspired oxygen (FiO2) and therefore reduces effectiveness of intended use. Higher flows have been demanded by the clinical community and are associated with a reduction of both PaCO2 and metabolic work. Newer High Flow devices offer higher flow rates up to 80 liters per minute. We examined whether the use of 60 and 80 liters per minute set flows would create an increased risk of gastric insufflation and possibly aspiration. Methods Bench study to compare the pressures generated using different flow rates in two commercially available HFNC devices in three different conditions: Open and closed system (mouth) breathing, breathing against active exhalation, and complete downstream occlusion. Results Our bench study found that high flow rate therapy did not elevate airway pressures to a level that would result in gastric distention and potential aspiration. In the open mouth test, the pressure ranged from minimum 0.2 to maximum of 1.3 cmH2O, and from minimum of 0.52 to 5.27 cmH2O in the closed mouth test. In the active breathing test, the pressures ranged from minimum 1.5 to 6 cmH2O. In the complete occlusion test, the pressures ranged from minimum 0.37 to 4.49 cmH2O. Conclusion Flows provided during HFNC therapy do not pose a hazard of creating high pressures which exceed esophageal opening pressure and pose a risk of gastric distention. The higher flow rates may reduce the risk associated with the potential false positive prediction of HFNC failure when therapy is not set to match the patient’s inspiratory peak flow demand. The benefit of higher flows to match the inspiratory demand provides a rarely recognized additional benefit of improving the accuracy of predictive indices such as the ROX index and allows for high flow therapy to more fully achieve its intended use.