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

<strong><em>Background:</em></strong> The mode of waveform generation and circuit characteristics differ between high-frequency oscillators. It is unknown if this influences performance. <b><i>Objectives:</i></b> 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. <b><i>Methods:</i></b> Oscillators were evaluated using a 70-ml test lung at 1.0 and 2.0 ml/cm H<sub>2</sub>O compliance, with mean airway pressures (P<sub>AW</sub>) of 10 and 20 cm H<sub>2</sub>O, frequencies of 5, 10 and 15 Hz, and an ETT diameter of 2.5 and 3.5 mm. At each permutation of P<sub>AW</sub>, frequency and ETT, the set ΔP was sequentially increased from 15 to 50 cm H<sub>2</sub>O, or from 20 to 100% maximum amplitude (10% increments) depending on the oscillator design. The ΔP at the ventilator (ΔP<sub>VENT</sub>), airway opening (ΔP<sub>AO</sub>) and within the test lung (ΔP<sub>TRACH</sub>), and tidal volume (V<sub>T</sub>) at the airway opening were determined at each set ΔP. <b><i>Results:</i></b> In 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<sub>VENT</sub>, ΔP<sub>AO</sub> and ΔP<sub>TRACH</sub> (all r<sup>2</sup> >0.93), with differing attenuation of the pressure wave. Delivered V<sub>T</sub> at the different settings tested varied between devices, with some unable to deliver V<sub>T</sub> >3 ml at 15 Hz, and others generating V<sub>T</sub> >20 ml at 5 Hz and a 1:1 inspiratory-to-expiratory time ratio. <b><i>Conclusions:</i></b> Clinicians should be aware that modern high-frequency oscillators exhibit important differences in the delivered ΔP and V<sub>T</sub>.