Mechanical ventilation guided by driving pressure optimizes local pulmonary biomechanics in an ovine model.

Mechanical ventilation exposes the lung to injurious stresses and strains that can negatively affect clinical outcomes in acute respiratory distress syndrome or cause pulmonary complications after general anesthesia. Excess global lung strain, estimated as increased respiratory system driving pressure, is associated with mortality related to mechanical ventilation. The role of small-dimension biomechanical factors underlying this association and their spatial heterogeneity within the lung are currently unknown. Using four-dimensional computed tomography with a voxel resolution of 2.4 cubic millimeters and a multiresolution convolutional neural network for whole-lung image segmentation, we dynamically measured voxel-wise lung inflation and tidal parenchymal strains. Healthy or injured ovine lungs were evaluated as the mechanical ventilation positive end-expiratory pressure (PEEP) was titrated from 20 to 2 centimeters of water. The PEEP of minimal driving pressure (PEEP_DP) optimized local lung biomechanics. We observed a greater rate of change in nonaerated lung mass with respect to PEEP below PEEP_DP compared with PEEP values above this threshold. PEEP_DP similarly characterized a breaking point in the relationships between PEEP and SD of local tidal parenchymal strain, the 95th percentile of local strains, and the magnitude of tidal overdistension. These findings advance the understanding of lung collapse, tidal overdistension, and strain heterogeneity as local triggers of ventilator-induced lung injury in large-animal lungs similar to those of humans and could inform the clinical management of mechanical ventilation to improve local lung biomechanics. Editor's summary: Mechanical ventilation is a life-sustaining tool for patients with compromised lungs but is also associated with a risk of damaging lung strain. Several ventilation parameters can be tuned by clinicians, including the amount of pressure applied at the end of expiration to maintain open alveoli [positive end-expiratory pressure (PEEP)]. The relationship between applied PEEP and small-scale lung strains is not well characterized. Here, Lagier et al. used four-dimensional computed tomography imaging with 2.4 mm³ voxel resolution in mechanically ventilated sheep to analyze localized changes in lung strain in healthy lungs and diseased lungs. They identified the PEEP of minimal respiratory driving pressure as a setting that marks a change in the relationship between PEEP settings and parameters of lung function and biomechanics. These findings will support future investigation in individualized mechanical ventilation. —Molly Ogle [ABSTRACT FROM AUTHOR]