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Multiple Transients of Local Gas Redistribution During Spontaneous Breathing Are Influenced by Ventilatory Settings
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A7213 - Multiple Transients of Local Gas Redistribution During Spontaneous Breathing Are Influenced by Ventilatory Settings
Author Block: G. Perchiazzi1, M. Pellegrini1, G. Hedenstierna2, A. Roneus1, A. S. Larsson1; 1Surgical Sciences, Uppsala University, Uppsala, Sweden, 2Medical Sciences, Uppsala University, Uppsala, Sweden.
Rationale. Gas redistribution inside the lung parenchyma has been related to inspiratory efforts and suggested as cause of occult overstretch in injured lungs during spontaneous breathing (1). Regional ventilation heterogeneity has been previously described during controlled ventilation in experimental models of ARDS (2, 3). Aim of the research is to investigate the effects of different lung volumes and airway resistances on the pattern of air redistribution during the course of the entire inspiration, during spontaneous breathing (SB) and controlled mechanical ventilation (MV) in a mild acute respiratory distress syndrome (ARDS) model.
Methods. Six anaesthetized, tracheostomized pigs underwent lung lavages to obtain mild ARDS (PO2/FIO2 of 250 mmHg). They were studied during SB with continuous positive airway pressure (CPAP) and during pressure control ventilation (PCV) after muscle-relaxation. During CPAP two different endotracheal tube sizes (9 mm: low inspiratory resistance and 6mm: high inspiratory resistance) were sequentially used. High rate (20Hz) dynamic CT scans were performed at six PEEP levels (from 15 to 0, in steps of 3 cmH2O) and at two distances from the diaphragm dome: at 1 (L1) and 4 (L4) cm. From the entire inspiratory CT sequence, six consecutive breaths per condition were analyzed. After image registration, consecutive CT images were subtracted to obtain delta volume (ΔV) images, which were analyzed by a quadtree decomposition algorithm to assess the magnitude of air redistribution. The mean area of all obtained squares (AreaSq) for each image was used as index of the magnitude of air-redistribution. The higher the mean area, the bigger the air-redistribution events. Student t-test (α=0.05) was applied for statistics.
Results. Multiple transients of local air redistribution occurred continuously throughout the entire inspiration both during SB and MV. Both regions with negative ΔV and regions with positive ΔV were detected. During SB, the AreaSq: 1.increased by decreasing PEEP; 2.was higher for high airway resistances; 3.was higher at L4 than at L1.
Conclusions. Air redistribution occurs throughout the inspiration, both during SB and MV. Its magnitude depends on lung volume, airway resistance and distance from the diaphragm. Macro-air-redistribution events are facilitated by ventilatory settings promoting lung collapse: low PEEP and high tube resistance. Proximity to the diaphragm stabilized the lung and reduced macro-air-redistribution. These findings emphasize the importance of optimizing ventilatory settings during SB in mild ARDS conditions.
Bibliography.
1) Yoshida T, et al. AJRCCM 2013
2) Perchiazzi, et al. Resp.Physiol.Neurobiol 2014
3) Wellman, et al. J Appl Physiol 2012
Author Block: G. Perchiazzi1, M. Pellegrini1, G. Hedenstierna2, A. Roneus1, A. S. Larsson1; 1Surgical Sciences, Uppsala University, Uppsala, Sweden, 2Medical Sciences, Uppsala University, Uppsala, Sweden.
Rationale. Gas redistribution inside the lung parenchyma has been related to inspiratory efforts and suggested as cause of occult overstretch in injured lungs during spontaneous breathing (1). Regional ventilation heterogeneity has been previously described during controlled ventilation in experimental models of ARDS (2, 3). Aim of the research is to investigate the effects of different lung volumes and airway resistances on the pattern of air redistribution during the course of the entire inspiration, during spontaneous breathing (SB) and controlled mechanical ventilation (MV) in a mild acute respiratory distress syndrome (ARDS) model.
Methods. Six anaesthetized, tracheostomized pigs underwent lung lavages to obtain mild ARDS (PO2/FIO2 of 250 mmHg). They were studied during SB with continuous positive airway pressure (CPAP) and during pressure control ventilation (PCV) after muscle-relaxation. During CPAP two different endotracheal tube sizes (9 mm: low inspiratory resistance and 6mm: high inspiratory resistance) were sequentially used. High rate (20Hz) dynamic CT scans were performed at six PEEP levels (from 15 to 0, in steps of 3 cmH2O) and at two distances from the diaphragm dome: at 1 (L1) and 4 (L4) cm. From the entire inspiratory CT sequence, six consecutive breaths per condition were analyzed. After image registration, consecutive CT images were subtracted to obtain delta volume (ΔV) images, which were analyzed by a quadtree decomposition algorithm to assess the magnitude of air redistribution. The mean area of all obtained squares (AreaSq) for each image was used as index of the magnitude of air-redistribution. The higher the mean area, the bigger the air-redistribution events. Student t-test (α=0.05) was applied for statistics.
Results. Multiple transients of local air redistribution occurred continuously throughout the entire inspiration both during SB and MV. Both regions with negative ΔV and regions with positive ΔV were detected. During SB, the AreaSq: 1.increased by decreasing PEEP; 2.was higher for high airway resistances; 3.was higher at L4 than at L1.
Conclusions. Air redistribution occurs throughout the inspiration, both during SB and MV. Its magnitude depends on lung volume, airway resistance and distance from the diaphragm. Macro-air-redistribution events are facilitated by ventilatory settings promoting lung collapse: low PEEP and high tube resistance. Proximity to the diaphragm stabilized the lung and reduced macro-air-redistribution. These findings emphasize the importance of optimizing ventilatory settings during SB in mild ARDS conditions.
Bibliography.
1) Yoshida T, et al. AJRCCM 2013
2) Perchiazzi, et al. Resp.Physiol.Neurobiol 2014
3) Wellman, et al. J Appl Physiol 2012
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