Mechanics of nasal mask-delivered HFOV in neonates: A physiologic study.

OBJECTIVES: To clarify if nasal mask influences noninvasive high-frequency oscillatory ventilation (NHFOV) mechanics to optimize the clinical use of nasal mask-delivered NHFOV.

WORKING HYPOTHESIS: Nasal mask may affect the mechanical efficacy of NHFOV.

METHODOLOGY: We designed a physiologic study composed of an in vitro phase aiming to investigate pressure transmission and volume delivery in a bench model of nasal mask-delivered NHFOV. In a second phase, we measured the leaks in vivo in a series of neonates receiving nasal mask-delivered NHFOV or other forms of noninvasive respiratory support with same nasal masks.

RESULTS: In vitro pressure transmission is lower with nasal mask (pressure at the lung [Plung]: 2 [0.8]), than with the endotracheal tube (Plung 9.5 [1.5] cmH2 O; P = 0.007). Same applies for volume delivery (Vol: 0.6 [0.2] vs 1.8 [0.5] mL; P = 0.0001). Increasing ventilatory boundaries slowly affects pressure and volume delivery. Ventilating the model with maximal parameters (∆P = 55 cmH2 O; frequency = 8 Hz) we obtained a Vol 1.5 (0.2) mL. The nasal mask provides lower volume delivery and ventilation, compared with nasal prongs studied in previously published studies. Changing frequency allows a better performance than changing ∆P. In vivo leaks are approximately 30% and are similar during NHFOV or other forms of nasal mask-delivered noninvasive ventilation.

CONCLUSIONS: Nasal mask-delivered NHFOV is feasible, but it may require more aggressive ventilatory parameters to increase volume delivery and ventilation. The use of the nasal mask is associated with some leaks, but this is independent from the type of noninvasive respiratory support applied.