Static respiratory compliance in anaesthetised and intubated brachycephalic dogs with and without brachycephalic obstructive airway syndrome.

The impact of brachycephalic obstructive airway syndrome in dogs (BOAS) on respiratory mechanics is unclear and may affect the choice of ventilation strategies during anaesthesia. This prospective study included 56 client-owned brachycephalic dogs, allocated to be BOAS (n = 26) or non-BOAS dogs (n = 30) based on functional grading. All dogs were anaesthetised using a standardised anaesthetic protocol. Pressure-controlled ventilation was initiated around 30 min post-induction, maintaining peak inspiratory pressure at 7-12 cm H2O. Static respiratory compliance (Cstat) was recorded at predetermined time points in sternal, right and left lateral recumbency. Thorax dimensions were assessed with a tape measure. Body surface area (BSA) was calculated and the ratio Cstat/BSA used as the main outcome variable. Comparison of means/medians, analysis of proportions, the Spearman correlation coefficient and both logistic and linear regression were used for data analysis. P < 0.05 was considered statistically significant. Non-BOAS dogs showed significantly higher Cstat/BSA compared to BOAS dogs in sternal (41.6 (31.1-51.8) vs. 32.9 (24.4 - 39.2), respectively, P = 0.028), right lateral (36.2 (25.7 - 46.4) vs. 27.0 (22.7 - 35.6); P = 0.026) and left lateral (33.6 (22.6 - 45.5) vs. 24.6 (18.4 - 32.2); P = 0.020) recumbencies. For all dogs, the Cstat/BSA ratio was higher in sternal compared to lateral recumbencies. BOAS dogs had a significantly shorter distance between thoracic inlet and last rib compared to non-BOAS dogs (20 ± 4 vs. 23 ± 6 cm, respectively; P = 0.043). Reduced respiratory compliance in BOAS-affected dogs should be considered during mechanical ventilation.