Evaluation of three tidal volumes (10, 12 and 15 mL kg) in dogs for controlled mechanical ventilation assessed by volumetric capnography: a randomized clinical trial.

OBJECTIVE

To evaluate three routinely used tidal volumes (V; 10, 12 and 15 mL kg) for controlled mechanical ventilation (CMV) in lung-healthy anaesthetized dogs by assessing alveolar ventilation (VT) 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 V of 10 (G), 12 (G) or 15 (G) mL kg. After induction CMV was started. End-tidal carbon dioxide tension was maintained at 4.7-5.3 kPa by changing the respiratory frequency (f; 6<f<30 breaths minute). 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 VT to body weight (VT kg) and airway DS to V (VD/V), Bohr's DS (VD), Enghoff's DS (VD) and the volume of expired carbon dioxide per breath (VTCO) were calculated. Mean airway pressure (MawP), f 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 f>30. VT kg (p=0.001) increased and VD (p=0.002) decreased with greater V. VTCO (p=0.017) increased and VD/V (p=0.006), VD (p=0.008) and f (p=0.002) decreased between G and G. PIP (p=0.013) was significantly higher in G compared with that in G and G. No changes were observed in MawP.

CONCLUSIONS AND CLINICAL RELEVANCE

A V of 15 mL kg is most appropriate for CMV in lung-healthy dogs (as evaluated by respiratory mechanics and VCap) and does not impair cardiovascular variables.