High flow nasal oxygen generates positive airway pressure in adult volunteers

Introduction The use of non-invasive ventilation (NIV) as an alternative to intubation in respiratory failure is associated with better outcomes in certain conditions. NIV is often poorly tolerated by patients hence precipitating the need for invasive ventilation. High flow nasal (HFN) oxygen delivery is a potential alternative to NIV as it delivers air and oxygen via a humidified circuit at flows greater than those traditionally used with a nasal interface. Body Studies of paediatric patient using high flow nasal oxygen therapy have been shown to have similar efficacy as nasal continuous positive airway pressure (CPAP). Although the degree of positive pressure and the effect of different flow rates on positive pressure generation have not been well defined or studied in the adult intensive care population. St. Vincent's Health Human Research and Ethics Committee granted approval to this study and also awarded a $3000 grant. Volunteers were fitted with the Fisher & Paykel high flow nasal interface (RT034) and pharyngeal pressures were recorded with flows from 0 to 60 L/min. Expiratory pressures with the mouth closed were higher than those with the mouth open and this was statistically significant (<0.001). Expiratory pressures were higher with the mouth closed and were statistically different (p < 0.001). EPPs were higher amongst female subjects compared to male subjects and were statistically different between genders for both open (p < 0.05) and closed (p < 0.001) measurements. Conclusion This study has demonstrated that high flow nasal therapy is associated with the generation of significant positive airway pressure in volunteers. In conclusion there is a degree of CPAP generated with the HFN therapy, which is flow dependent and also dependent on whether the person is breathing with mouth open or closed.