OBJECTIVE: To evaluate three routinely used tidal volumes (VT; 10, 12 and 15 mL kg-1) for controlled mechanical ventilation (CMV) in lung-healthy anaesthetized dogs by assessing alveolar ventilation (VTalv) and dead space (DS).
STUDY DESIGN: Prospective, randomized clinical trial.
ANIMALS: A total of 36 client-owned dogs.
METHODS: Dogs were randomly allocated to a VT of 10 (G10), 12 (G12) or 15 (G15) mL kg-1. After induction CMV was started. End-tidal carbon dioxide tension was maintained at 4.7-5.3 kPa by changing the respiratory frequency (fR; 6<fR<30 breaths minute-1). After 29 minutes, cardiovascular and respiratory variables were recorded for 3 minutes using a multiparameter monitor, volumetric capnography (VCap) and a blood gas analyser. The ratios of VTalv to body weight (VTalv kg-1) and airway DS to VT (VDaw/VT), Bohr's DS (VDBohr), Enghoff's DS (VDBE) and the volume of expired carbon dioxide per breath (VTCO2,br) were calculated. Mean airway pressure (MawP), fR and peak inspiratory pressure (PIP) were recorded. Data were analysed using one-way anova and Student-Newman-Keuls tests with a statistical significance set at p<0.05.
RESULTS: No differences were observed for demographic data and cardiovascular variables between groups. A total of three dogs were excluded because of technical difficulties and one because of fR>30. VTalv kg-1 (p=0.001) increased and VDBohr (p=0.002) decreased with greater VT. VTCO2,br (p=0.017) increased and VDaw/VT (p=0.006), VDBE (p=0.008) and fR (p=0.002) decreased between G10 and G15. PIP (p=0.013) was significantly higher in G15 compared with that in G10 and G12. No changes were observed in MawP.
CONCLUSIONS AND CLINICAL RELEVANCE: A VT of 15 mL kg-1 is most appropriate for CMV in lung-healthy dogs (as evaluated by respiratory mechanics and VCap) and does not impair cardiovascular variables.