High-frequency oscillatory ventilation: lessons learned from mechanical test lung models.

Abstract

OBJECTIVE: Review data obtained from high-frequency oscillatory ventilation (HFOV) and mechanical test lung models with respect to delivered tidal volume, distal pressure transmission, endotracheal tube cuff leaks, and simulated clinical conditions. DESIGN: Review of selected studies from PubMed, published abstracts, and institutional mechanical test lung data. RESULTS: Tidal volume delivery during HFOV is altered by oscillatory pressure amplitude (DeltaP), frequency (Hz), percent inspiratory time (IT%), and patient variables. Distal (carinal) oscillatory pressure amplitude transmission is directly correlated with endotracheal tube diameter and peripheral airway resistance. Endotracheal tube cuff leaks promote egress of tracheal gas while attenuating distal oscillatory pressure amplitude and tidal volume transmission. Simulated clinical conditions (e.g., increased distal airway resistance, mainstem intubation) may increase observed DeltaP, whereas mean airway pressure is decreased with air leaks. CONCLUSION: Mechanical test lung and artificial trachea simulations may provide useful information on the interaction of HFOV with altered lung mechanics and may contribute to the formulation of HFOV clinical strategies. Important limitations of these models include absence of gas exchange, histologic and biologic markers, or hemodynamic data.