The Effects of Flow on Airway Pressure During Nasal High-Flow Oxygen Therapy

BACKGROUND: Nasal high-flow oxygen therapy increases the mean nasopharyngeal airway pressure in adults, but the relationship between flow and pressure is not well defined. OBJECTIVE: To determine the relationship between flow and pressure with the Optiflow nasal high-flow oxygen therapy system. METHODS: We invited patients scheduled for elective cardiac surgery to participate. Measurements were performed with nasal high-flow oxygen at flows of 30, 40, and 50 L/min, with the patient's mouth both open and closed. Pressures were recorded over one minute of breathing, and average flows were calculated via simple averaging. RESULTS: With the mouth closed, the mean +/- SD airway pressures at 30, 40, and 50 L/min were 1.93 +/- 1.25 cm H2O, 2.58 +/- 1.54 cm H2O, and 3.31 +/- 1.05 cm H2O, respectively. There was a positive linear relationship between flow and pressure. CONCLUSIONS: The mean nasopharyngeal pressure during nasal high-flow oxygen increases as flow increases. (Australian Clinical Trials Registry http://www.adhb.govt.nz/achicu/hot_2_airway_pressure.htm)