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A5126 - Onset and Magnitude of Pendelluft During Spontaneous Breathing Depend on Lung Volume
Author Block: M. Pellegrini1, G. Hedenstierna2, A. Roneus1, A. S. Larsson1, G. Perchiazzi1; 1Surgical Sciences, Uppsala University, Uppsala, Sweden, 2Medical Sciences, Uppsala University, Uppsala, Sweden.
Rationale. Pendelluft phenomena, characterized by movements of air from non-dependent to dependent regions of lung parenchyma before the onset on inspiratory flow, have been described as a consequence of spontaneous breathing (SB) efforts in injured lungs (1). These events have been designated as a potential cause of lung overdistension leading to patient self-inflicted lung injury (P-SILI) (2). To investigate the effects of different lung volumes on the onset, magnitude and topographical distribution of pendelluft, in a mild acute respiratory distress syndrome (ARDS) animal model, both during spontaneous breathing (SB) and controlled mechanical ventilation (MV). Methods. Six anaesthetized, tracheostomized pigs underwent lung lavages to obtain mild ARDS (PO2/FIO2 of 250). We studied SB during continuous positive airway pressure (CPAP) ventilation and then MV during pressure control ventilation (PCV) in the same animals, during muscle relaxation. High rate (20Hz) dynamic simultaneous CT scans were performed at different lung volumes created by six positive end expiratory pressures (CPAP/PEEP) levels (15 to 0, in steps of 3 cmH2O) at two distances (at 1 (L1) and 4 (L4) cm) from the diaphragm dome. Consecutive CT images were subtracted to obtain delta volume maps (ΔVm), representing the distribution of the local volume changes. For each studied breath, the first 3 ΔVm, at the beginning of inspiration, before the onset of inspiratory flow, were selected and analyzed. Each ΔVm image was divided in 4 consecutive regions of interest (ROI1, ROI2, ROI3, ROI4) along the gravitational axis. Statistics: Student t-test (α=0.05). Results. Pendelluft events occurred during all SB conditions. High CPAP values (15-9 cmH2O) were characterized by a more homogeneous distribution of gas inside the different ROIs, when compared to lower CPAP. CPAP values lower than 6 cmH2O significantly enhanced the onset of pendelluft both from non-dependent (ROI1) to dependent lung regions (ROI4) and from more cranial (L4) to more caudal (L1) lung regions. With PCV, independent from PEEP settings, there were no pendelluft events at the beginning of inspiration. Conclusions. In injured lungs, initial temporary pendelluft events before the onset of inspiratory flow appear during SB at low CPAP levels. Pendelluft magnitude and its topographical distribution are influenced by CPAP level. The presented results emphasized the importance of optimizing the ventilatory settings during SB to avoid P-SILI. Bibliography. 1) Yoshida T, et al. AJRCCM 2013; 188:1420-7 2) Brochard L, et al. AJRCCM 2017; 195:1-16