R04 - Effect of chest confirmation on measured expiratory volumes and lung mechanics in healthy dogs

Abstract: Background – In people with acute respiratory distress syndrome (ARDS), ventilation with lower tidal volumes has been associated with improved outcome. However, chest conformation in dogs is more variable than in people and it is unclear if different chest confirmations can influence lung mechanics. Hypothesis/Objectives – To prospectively evaluate lung volumes and dynamic compliance in healthy dogs with different chest conformation. Animals – Healthy dogs undergoing anesthesia for treatment of a non-pulmonary condition. Methods – Dogs were classified as having a keel (e.g. Setter), barrel (e.g. Labrador) or flat (e.g. Bulldog) chest based upon measurement of the thoracic depth:width ratio. Dogs were anesthetized, connected to a critical care ventilator and provided pressure-limited ventilation to a peak inspiratory pressure of 25 cmH2O to measure expiratory volume. Next, lung mechanics were measured with volume-limited ventilation. Continuous data for each group were compared with one-way ANOVA and Tukey post-hoc test for multiple comparisons. Results – 42 dogs were enrolled, 14 in each group. The mean expiratory volume was significantly lower in flat-chested dogs (28.1 0.4 mL/kg) compared to that of keel-chested dogs (31.55.9 mL/kg, p=.041). Flat-chested dogs also had significantly lower dynamic compliance (1.39 .23 mL/cm H2O/kg) than keel-chested (1.500.41 mL/cm H2O/kg, p=.023) and barrel-chested dogs (1.7050.21 mL/cm H2O/kg, p=.011). Conclusions and Clinical Importance – Flat-chested dogs have a lower lung volume for a given inflation pressure and subsequently lower compliance. Chest conformation impact lung mechanics, and separate guidelines should exist for ventilatory settings.