ICU · Respiratory / ventilation

High-Frequency Oscillatory Ventilation (HFOV)

Also known as HFOV · High-frequency oscillatory ventilation · High-frequency ventilation · OSCILLATE trial · OSCAR trial · MOAT trial · Mean airway pressure · mPaw · Pendelluft · Taylor dispersion · Bias flow · Power (amplitude) · Open-lung strategy

High-frequency oscillatory ventilation (HFOV) is characterised by the rapid delivery of small tidal volumes together with the application of high mean airway pressures — the open-lung, lung-protective concept (Chan 2007; Fessler 2007: adult frequency typically 6 Hz or less, generous mean airway pressures). Gas exchange occurs not by bulk tidal flow alone but by five combined transport mechanisms (direct alveolar ventilation, convective mixing among units of unequal time constants, asymmetric velocity-profile convection, longitudinal/Taylor dispersion, and molecular diffusion; Chang 1984, who also showed increasing tidal volume improves gas exchange more effectively than increasing frequency). Oxygenation is managed through mean airway pressure and FiO2, CO2 clearance through pressure amplitude and frequency. Two landmark trials in adult ARDS were negative: the OSCILLATE trial (NEJM 2013, stopped early) found in-hospital mortality 47% vs 35% (RR 1.33) — HFOV 'does not reduce, and may increase' in-hospital mortality; the OSCAR trial (NEJM 2013) found no significant effect on 30-day mortality (41.7% vs 41.1%); a Cochrane review (2016) found no mortality reduction (RR 0.92) and does not support first-line use. HFOV is therefore NOT recommended for routine adult ARDS — at most a rarely-used rescue.