Introduction: Protective Conventional Mechanical Ventilation (CMV) has substantially improved outcomes in patients with ARDS over the last two decades, although mortality remains unacceptably high. We hypothesized that multi-frequency ventilation (MFV), in which small volume oscillations at multiple frequencies are added to a CMV waveform, would improve lung aeration and ventilation homogeneity, as assessed by quantitative Computed Tomography (qCT).
Methods: Twenty-five pigs were mechanically ventilated using a hybrid ventilator/oscillator (OscillaVent Inc., Iowa City, Iowa). Lung injury was induced by intravenous infusion of oleic acid, after which the animals were randomized to receive: 1) Protective CMV; 2) high frequency oscillatory ventilation (HFOV) per established protocol; or 3) MFV with a waveform consisting of 3.5 and 7 Hz oscillations superimposed on a CMV waveform. For each group, seven whole-lung CT scans were obtained during static breath holds from 30 to 0 cmH2O, in decrements of 5 cmH2O. Images were obtained at five time points, including before and immediately after lung injury, as well as 3-hour intervals thereafter. Quantitative CT analyses, including aeration and texture assessment, were performed on each segmented image.
Results: Air volume decreased with reduced pressure at each time point and was significantly higher in HFOV compared to CMV. Aeration analysis revealed a higher percentage of non-aerated regions during CMV compared to MFV and HFOV, with significant increases with decreasing pressure. Normally aerated regions were more prevalent during HFOV than in CMV, and decreased with decreasing airway pressure. Texture analysis showed a significant increase in consolidated areas with decreasing pressure, with higher values in CMV compared to MFV and HFOV.
Conclusions: This study shows that in a porcine model of ARDS, both MFV and HFOV improved lung aeration and reduced consolidation compared to CMV. MFV demonstrated results similar to HFOV, but with lower mean airway pressures. These findings suggest that MFV may offer similar benefits in lung recruitment and ventilation homogeneity compared to HFOV, with less risk of hemodynamic impairment. Further research is needed to assess the clinical applicability of MFV in patients, and its long-term effects in ARDS management.
