Examinando por Autor "Araos, J."

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    Distribution and Magnitude of Regional Volumetric Lung Strain and Its Modification by PEEP in Healthy Anesthetized and Mechanically Ventilated Dogs
    (2297-1769, 2022-03) Araos, J.; Cruces, P.; Martin-Flores, M.; Donati, P.; Gleed, R.; Boullhesen-Williams, T.; Perez, A.; Staffieri, F.; Retamal, J.; Vidal, M.; Hurtado, D.
    The present study describes the magnitude and spatial distribution of lung strain in healthy anesthetized, mechanically ventilated dogs with and without positive end-expiratory pressure (PEEP). Total lung strain (LSTOTAL) has a dynamic (LSDYNAMIC) and a static (LSSTATIC) component. Due to lung heterogeneity, global lung strain may not accurately represent regional total tissue lung strain (TSTOTAL), which may also be described by a regional dynamic (TSDYNAMIC) and static (TSSTATIC) component. Six healthy anesthetized beagles (12.4 ± 1.4 kg body weight) were placed in dorsal recumbency and ventilated with a tidal volume of 15 ml/kg, respiratory rate of 15 bpm, and zero end-expiratory pressure (ZEEP). Respiratory system mechanics and full thoracic end-expiratory and end-inspiratory CT scan images were obtained at ZEEP. Thereafter, a PEEP of 5 cmH2O was set and respiratory system mechanics measurements and end-expiratory and end-inspiratory images were repeated. Computed lung volumes from CT scans were used to evaluate the global LSTOTAL, LSDYNAMIC, and LSSTATIC during PEEP. During ZEEP, LSSTATIC was assumed zero; therefore, LSTOTAL was the same as LSDYNAMIC. Image segmentation was applied to CT images to obtain maps of regional TSTOTAL, TSDYNAMIC, and TSSTATIC during PEEP, and TSDYNAMIC during ZEEP. Compliance increased (p = 0.013) and driving pressure decreased (p = 0.043) during PEEP. PEEP increased the end-expiratory lung volume (p < 0.001) and significantly reduced global LSDYNAMIC (33.4 ± 6.4% during ZEEP, 24.0 ± 4.6% during PEEP, p = 0.032). LSSTATIC by PEEP was larger than the reduction in LSDYNAMIC; therefore, LSTOTAL at PEEP was larger than LSDYNAMIC at ZEEP (p = 0.005). There was marked topographic heterogeneity of regional strains. PEEP induced a significant reduction in TSDYNAMIC in all lung regions (p < 0.05). Similar to global findings, PEEP-induced TSSTATIC was larger than the reduction in TSDYNAMIC; therefore, PEEP-induced TSTOTAL was larger than TSDYNAMIC at ZEEP. In conclusion, PEEP reduced both global and regional estimates of dynamic strain, but induced a large static strain. Given that lung injury has been mostly associated with tidal deformation, limiting dynamic strain may be an important clinical target in healthy and diseased lungs, but this requires further study.
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    Effect of a lung rest strategy during ECMO in a porcine acute lung injury model
    (SpringerOpen, 2015-10) Araos, J.; Cruces, P.; Tapia, P.; Alegria, L.; García, P.; Salomon, T.; Rodriguez, F.; Amthauer, M.; Castro, G.; Erranz, B.; Soto, D.; Carreño, P.; Medina, T.; Damiani, F.; Bugedo, G.; Bruhn, A.
    Introduction ECMO is used to treat patients who develop refractory hypoxemia and to provide a more protective ventilation. Several guidelines recommend “lung rest” strategies based on variable ventilatory parameters. However, there is limited evidence to support this strategy. Objectives To compare the effect of a lung rest strategy based on near-apneic ventilation (Vt 1-2 ml/kg, PEEP 10, respiratory rate-RR 5 min) versus conventional (Vt 10ml/kg, PEEP 5, RR 20/min), and standard protective ventilation (Vt 6ml/kg, PEEP 10, RR 20/min). Methods Twenty-four domestic pigs (26-36 kg) were anesthetized, mechanically ventilated (Vt 10 ml/kg, PEEP 5, O2 1.0) and invasively monitored. Six animals were used as Sham. In the other 18 lung injury was induced by saline lavages (30 ml/kg per lavage) performed repeatedly in both supine and prone position until PaO2/FiO2 dropped below 250. They were then subjected to a 2-hour injurious ventilation with PCV, PEEP = 0, Pinsp = 40 cmH2O, RR = 10/min, I:E = 1:1, one hour in prone and the other in supine. After completing lung injury (time 0) animals were connected to a saline primed-MEDOS Hilite ECMO circuit by inserting a AVALON 23F double-lumen cannula through the external jugular vein. Blood flow was set at 60-70% of cardiac output. Animals were randomized into one of the three groups and ventilated according to randomization for the following 24 hours. Respiratory and hemodynamic data were collected at times 0, 3, 6, 12, 18 and 24h. After euthanizing animals at time 24h, tissue samples were extracted from the lungs and injury evaluated and scored by light microscopy. Total lung water content was estimated by the wet-dry weight ratio. Results PaO2 decreased significantly in all groups after injury, but was progressively restored after ECMO start, despite the study group. Mean arterial pressure remained within normal limits throughout the study period, whereas MPAP increased significantly after injury but reached values close to SHAM soon after ECMO initiation. Lung wet-dry weight ratio and histological injury score increased significantly in all study groups compared to SHAM. Although non-significant, there was a trend towards a better histological injury score when Vt was reduced. Conclusions In this preliminary analysis, we found no clear advantage of reducing Vt when applying ECMO to support a double-hit animal model of ARDS in regard to resolution of lung edema or gas exchange. However, further work is required to determine if the non-significant reduction in lung injury observed in the near-apneic strategy may be relevant in providing further protection to the injured lungs supported by ECMO. © 2015 Araos et al.