The use of ventilator-acquired pulmonary mechanics and computed tomography in the assessment of interventions for experimental feline asthma

Abstract

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] In an experimental model of feline asthma, computed tomography (CT) and ventilator-acquired pulmonary mechanics were used in the assessment of various conditions. Bronchoalveolar lavage (BAL) was performed to induce airflow limitation. First, it was hypothesized that the use of positive end-expiratory pressure (PEEP) at 2 cmH₂O or inspired oxygen concentration of 30% would improve pulmonary mechanics and decrease evidence of atelectasis compared with no PEEP or 100% O₂ in cats undergoing BAL. Secondly, it was hypothesized that heliox-driven nebulization of albuterol (heliox/albuterol) would lead superior reduction in airflow limitation and CT documented anatomic changes compared with heliox/saline, nitrox/albuterol or nitrox/saline 24 hrs post-allergen challenge and 5 minutes post-BAL. In the first study, the use of 30% inspired oxygen concentration failed to show any significant improvement in pulmonary mechanics but did diminish atelectasis. It was also associated with further desaturation of hemoglobin in some cats. The modest levels of PEEP employed were without effect on any of our outcome parameters. In the second study, heliox failed to demonstrate any benefit in terms of oxygenation, pulmonary mechanics, or CT features. As expected, nebulized albuterol improved peak airway pressure when compared with saline nebulization. In this study mechanical ventilation and the use of PEEP may have altered our outcome parameters, especially in regard to CT attenuation and portions of lung aeration.