Does High-Frequency Ventilation Have Still a Role Among the Current Ventilatory Strategies?

After the decline of the “iron lung,” mechanical ventilation is currently based on intermittent positive pressure (IPPV). Accordingly, a “positive” pressure (i.e., greater than the atmospheric pressure) inflates the tidal volume (VT), while expiration is passive, due to the elastic return of the respiratory system. During IPPV, the mean airway opening pressure (PAO, MEAN) depends on the pressure applied to supply the VT, on the eventual level of positive end-expiratory pressure (PEEP), and, on a lesser extent, on respiratory rate (RR) and inspiratory time (TINSP). High-frequency oscillation ventilation (HFO) is an alternative technique that applies a constant lung-distending pressure with superimposed small pressure oscillations (±2–4 cmH2O) delivered at very high rate (between 180 and 900 cycles per minute) [1, 2]. The resulting VTs are smaller than the anatomic dead space (between 1 and 3 ml/kg) and therefore the CO2 is not cleared by alveolar ventilation as happens with IPPV, but through “unconventional” mechanisms (see below).