Are All Oscillators Created Equal? In vitro Performance Characteristics of Eight High-Frequency Oscillatory Ventilators

Background: The mode of waveform generation and circuit characteristics differ between high-frequency oscillators. It is unknown if this influences performance.

Objectives: To describe the relationships between set and delivered pressure amplitude (ΔP), and the interaction with frequency and endotracheal tube (ETT) diameter, in eight high-frequency oscillators.

Methods: Oscillators were evaluated using a 70-ml test lung at 1.0 and 2.0 ml/cm H₂O compliance, with mean airway pressures (P_AW) of 10 and 20 cm H₂O, frequencies of 5, 10 and 15 Hz, and an ETT diameter of 2.5 and 3.5 mm. At each permutation of P_AW, frequency and ETT, the set ΔP was sequentially increased from 15 to 50 cm H₂O, or from 20 to 100% maximum amplitude (10% increments) depending on the oscillator design. The ΔP at the ventilator (ΔP_VENT), airway opening (ΔP_AO) and within the test lung (ΔP_TRACH), and tidal volume (V_T) at the airway opening were determined at each set ΔP.

Results: IIn two oscillators the relationships between set and delivered ΔP were non-linear, with a plateau in ΔP thresholds noted at all frequencies (Dräger Babylog 8000) or ≥10 Hz (Dräger VN500). In all other devices there was a linear relationship between ΔP_VENT, ΔP_AO and ΔP_TRACH (all r² >0.93), with differing attenuation of the pressure wave. Delivered V_T at the different settings tested varied between devices, with some unable to deliver V_T >3 ml at 15 Hz, and others generating V_T >20 ml at 5 Hz and a 1:1 inspiratory-to-expiratory time ratio.

Conclusions: Clinicians should be aware that modern high-frequency oscillators exhibit important differences in the delivered ΔP and V_T.