![]() ![]() The study was approved by the Ethics Committees for Animal Research at the Faculty of Veterinary Medicine and Animal Science of the University of São Paulo (FMVZ-USP protocol number 110/8) and Faculty of Medicine of the University of São Paulo (CEUA-USP protocol number 100/10). The hypothesis of the study was that low inspiratory pressures would result in more areas of lung collapse, while high inspiratory pressures would result in more areas of overinflation in healthy cat lungs. The aim of this study was to assess the inspiratory lung aeration distribution by helical CT and respiratory mechanics in anesthetized cats ventilated with 6 different levels of inspiratory pressure (5, 7, 9, 11, 13, and 15 cmH2O) to obtain the best value of inspiratory pressure to ventilate healthy lungs. Using this technique, it is possible to precisely compute the amount of lung parenchyma overinflation in diverse inspiratory pressure conditions, allowing the identification of less harmful ventilatory strategies ( 9– 12). The quantitative assessment of the distribution of aeration within the lungs during MV can be evaluated using CT ( 8). The current ventilation monitoring methods available at the bedside are unable to detect lung hyperinflation. Despite the evidence in other species, to the authors' knowledge, there is no evidence describing the pulmonary aeration distribution of healthy cats undergoing positive pressure ventilation in relation to lung hyperinflation and alveolar collapse. Hyperinflation can lead to pulmonary lesions by cyclical stretching of lung tissues, promoting inflammation, acute lung injury, and postoperative complications ( 5– 7). However, it may lead to the development of areas of atelectasis and hyperinflation within the pulmonary parenchyma ( 1– 4). Mechanical ventilation (MV) aids in maintaining adequate pulmonary gas exchange during general anesthesia for surgical procedures. This fact can be controlled by increasing or decreasing respiratory rate and inspiratory time. The increase in airway pressure promoted an elevation in pH ( p < 0.001).Ĭonclusions and Clinical Relevance: Ventilation with 5 and 7 cmH 2O of airway pressure prevents overinflation in healthy cats with highly compliant chest walls, despite presenting acidemia by respiratory acidosis. A progressive decrease was observed in arterial carbon dioxide partial pressure (PaCO 2) and end-tidal carbon dioxide (ETCO 2) when the airway pressures were increased above 9 cmH 2O ( p < 0.001). Tidal volume and overinflated lung fraction returned to baseline when airway pressure was decreased. Increases in airway pressure were associated with progressive distention of the lung parenchyma. Result: At 5 cmH 2O airway pressure, tidal volume was 6.7± 2.2 ml kg −1, 2.1% (0.3–6.3%) of the pulmonary parenchyma was overinflated and 84.9% (77.6%−87.6%) was normally inflated. Lung parenchyma aeration was defined as overinflated, normally-aerated, poorly-aerated, and non-aerated according to the CT attenuation number (−1,000 to −900 HU, −900 to −500 HU, −500 to −100 HU, and −100 to +100 HU, respectively). After 5 min in each inspiratory pressure step, a 4 s inspiratory pause was performed to obtain a thoracic juxta-diaphragmatic single slice helical CT image and to collect respiratory mechanics data and an arterial blood sample. The respiratory rate was set at 15 movements per min and end-expiratory pressure at zero (ZEEP). Methods: Seventeen adult male cats were ventilated in pressure-controlled mode with airway pressure stepwise increased from 5 to 15 cmH 2O in 2 cmH 2O steps every 5 min and then stepwise decreased. Study Design: Prospective laboratory study.Īnimals: A group of 17 healthy male cats, aged 1.9–4.5 years and weighing 3.5 ± 0.5 kg. Objective: This study aimed to evaluate lung overinflation at different airway inspiratory pressure levels using computed tomography in cats undergoing general anesthesia. 5Discipline of Anesthesiology, Faculdade de Medicina da Universidade de São Paulo, São Paulo, Brazil.4Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California Davis, Davis, CA, United States.3Department of Clinical Sciences, School of Veterinary Medicine, North Caroline State University, Raleigh, NC, United States.2Department of Surgery, School of Veterinary Medicine and Animal Science, University of São Paulo, São Paulo, Brazil.1UFAPE Veterinary Intensive Care Unit, São Paulo, Brazil. ![]() Pinto 2 Lenin Arturo Villamizar-Martinez 3 João H. ![]()
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