Browsing by Author "Staffieri, Francesco"

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    Distribution and Magnitude of Regional Volumetric Lung Strain and Its Modification by PEEP in Healthy Anesthetized and Mechanically Ventilated Dogs
    (2022) Araos, Joaquin; Cruces, Pablo; Martin-Flores, Manuel; Donati, Pablo; Gleed, Robin D.; Boullhesen-Williams, Tomas; Perez, Agustin; Staffieri, Francesco; Retamal, Jaime; Melo, Marcos Vidal F.; Hurtado, Daniel E.
    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 cmH(2)O 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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    Evaluation of Lung Aeration and Respiratory System Mechanics in Obese Dogs Ventilated With Tidal Volumes Based on Ideal vs. Current Body Weight
    (2021) Araos, Joaquin; Lacitignola, Luca; de Monte, Valentina; Stabile, Marzia; Porter, Ian; Hurtado, Daniel E.; Perez, Agustin; Crovace, Antonio; Grasso, Salvatore; Martin-Flores, Manuel; Staffieri, Francesco
    We describe the respiratory mechanics and lung aeration in anesthetized obese dogs ventilated with tidal volumes (VT) based on ideal (VTi) vs. current (VTc) body weight. Six dogs with body condition scores >= 8/9 were included. End-expiratory respiratory mechanics and end-expiratory CT-scan were obtained at baseline for each dog. Thereafter, dogs were ventilated with VT 15 ml kg(-1) based on VTi and VTc, applied randomly. Respiratory mechanics and CT-scan were repeated at end-inspiration during VTi and VTc. Data analyzed with linear mixed models and reported as mean +/- SD or median [range]. Statistical significance p < 0.05. The elastance of the lung, chest wall and respiratory system indexed by ideal body weight (IBW) were positively correlated with body fat percentage, whereas the functional residual capacity indexed by IBW was negatively correlated with body fat percentage. At end-expiration, aeration (%) was: hyperaeration 0.03 [0.00-3.35], normoaeration 69.7 [44.6-82.2], hypoaeration 29.3 [13.6-49.4] and nonaeration (1.06% [0.37-6.02]). Next to the diaphragm, normoaeration dropped to 12 +/- 11% and hypoaeration increased to 90 +/- 8%. No differences in aeration between groups were found at end-inspiration. Airway driving pressure (cm H2O) was higher (p = 0.002) during VTc (9.8 +/- 0.7) compared with VTi (7.6 +/- 0.4). Lung strain was higher (p = 0.014) during VTc (55 +/- 21%) than VTi (38 +/- 10%). The stress index was higher (p = 0.012) during VTc (SI = 1.07 [0.14]) compared with VTi (SI = 0.93 [0.18]). This study indicates that body fat percentage influences the magnitude of lung, chest wall, and total respiratory system elastance and resistance, as well as functional residual capacity. Further, these results indicate that obese dogs have extensive areas of hypoaerated lungs, especially in caudodorsal regions. Finally, lung strain and airway driving pressure, surrogates of lung deformation, are higher during VTc than during VTi, suggesting that in obese anesthetized dogs, ventilation protocols based on IBW may be advantageous.
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    Preliminary evaluation of the effects of a 1:1 inspiratory-to-expiratory ratio in anesthetized and ventilated horses
    (2022) Pittman, Ella; Martin-Flores, Manuel; Mosing, Martina; Lorenzutti, Matías; Retamal Montes, Jaime; Staffieri, Francesco; Adler, Andy; Campbell, Mark; Araos, Joaquín
    Objective: To describe some cardiorespiratory effects of an inspiratory-to-expiratory (IE) ratio of 1:1 compared with 1:3 in ventilated horses in dorsal recumbency. Study design: Randomized crossover experimental study. Animals: A total of eight anesthetized horses, with 444 (330–485) kg body weight [median (range)]. Methods: Horses were ventilated in dorsal recumbency with a tidal volume of 15 mL kg–1 and a respiratory rate of 8 breaths minute–1, and IE ratios of 1:1 (IE1:1) and 1:3 (IE1:3) in random order, each for 25 minutes after applying a recruitment maneuver. Spirometry, arterial blood gases and dobutamine requirements were recorded in all horses during each treatment. Electrical impedance tomography (EIT) data were recorded in four horses and used to generate functional EIT variables including regional ventilation delay index (RVD), a measure of speed of lung inflation, and end-expiratory lung impedance (EELI), an indicator of functional residual capacity (FRC). Results were assessed with linear and generalized linear mixed models. Results: Compared with treatment IE1:3, horses ventilated with treatment IE1:1 had higher mean airway pressures and respiratory system compliance (p < 0.014), while peak, end-inspiratory and driving airway pressures were lower (p < 0.001). No differences in arterial oxygenation or dobutamine requirements were observed. PaCO2 was lower in treatment IE1:1 (p = 0.039). Treatment IE1:1 resulted in lower RVD (p < 0.002) and higher EELI (p = 0.023) than treatment IE1:3. Conclusions and clinical relevance: These results suggest that IE1:1 improved respiratory system mechanics and alveolar ventilation compared with IE1:3, whereas oxygenation and dobutamine requirements were unchanged, although differences were small. In the four horses where EIT was evaluated, IE1:1 led to a faster inflation rate of the lung, possibly the result of increased FRC. The clinical relevance of these findings needs to be further investigated.