High flow nasal cannula: Influence of gas type and flow rate on airway pressure and CO 2 clearance in adult nasal airway replicas.

•Airway gas washout and pressure during high flow therapy was measured using adult airway replicas.•Increasing cannula flowrate resulted in greater gas washout from the airways.•Cannula size and gas type had only minor influence on gas washout.•Airway pressure increased with cannula flow rate approximately quadratically.•Administration of heliox resulted in lower airway pressures than those for air or oxygen.