Abstract
Mechanical ventilation strategies that reduce the heterogeneity of regional lung stress and strain may reduce the risk of ventilator-induced lung injury (VILI). In this study, we used registration of four-dimensional computed tomographic (4DCT) images to assess regional lung aeration and deformation in 10 pigs under baseline conditions and following acute lung injury induced with oleic acid. CT images were obtained via dynamic axial imaging (Siemens SOMATOM Force) during conventional pressure-controlled mechanical ventilation (CMV), as well as high-frequency and multi-frequency oscillatory ventilation modalities (HFOV and MFOV, respectively). Our results demonstrate that oscillatory modalities reduce intratidal strain throughout the lung in comparison to conventional ventilation, as well as the spatial gradients of dynamic strain along the dorsal-ventral axis. Harmonic distortion of parenchymal deformation was observed during HFOV with a single discrete sinusoid delivered at the airway opening, suggesting inherent mechanical nonlinearity of the lung tissues. MFOV may therefore provide improved lung-protective ventilation by reducing strain magnitudes and spatial gradients of strain compared to either CMV or HFOV.
Highlights
Ventilator-induced lung injury (VILI) may inadvertently occur in critically ill patients receiving mechanical ventilation, due to the harmful stresses and strains associated with gas flows driven under positive pressure (Slutsky and Ranieri, 2013)
We demonstrated that oscillatory ventilation improves the average regional lung strain, as well as the spatial gradients of lung strain, compared to a conventional pressure-controlled modality in pigs with heterogeneous lung injury
In an oleic acid model of porcine acute respiratory distress syndrome (ARDS), high-frequency and multi-frequency oscillatory ventilation resulted in improved gas exchange efficiency and reduced regional lung strain compared to conventional mechanical ventilation
Summary
Ventilator-induced lung injury (VILI) may inadvertently occur in critically ill patients receiving mechanical ventilation, due to the harmful stresses and strains associated with gas flows driven under positive pressure (Slutsky and Ranieri, 2013). High-frequency oscillatory ventilation (HFOV) has been proposed as a rescue treatment for refractory hypoxemia in ARDS, given its theoretically ideal qualities for lung-protection: small tidal volumes that mitigate the risk of dynamic strain injury (i.e., volutrauma), and high mean airway pressures that prevent cyclic recruitment/derecruitment (i.e., atelectrauma) (Sklar et al, 2017). Despite an extensive history of scientific and clinical research over several decades, optimal strategies for HFOV initiation and management remain a subject of controversy (Malhotra and Drazen, 2013; Kneyber and Markhorst, 2016; Nguyen et al, 2016) As it is currently delivered, HFOV may not be an appropriate ventilatory modality in many patients with ARDS for several reasons. High frequency oscillatory flows are distributed in a heterogeneous and frequencydependent manner, predisposing overventilated regions to excess mechanical strain, and underventilated regions to derecruitment and atelectasis (Amini and Kaczka, 2013; Herrmann et al, 2016)
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