OBJECTIVE To evaluate the impact of 2 tidal volumes (T _V s) with or without positive end-expiratory pressure (PEEP) on lung mechanics, aeration, and gas exchange in healthy anesthetized dogs.

ANIMALS 40 mixed-breed dogs with healthy lungs.

PROCEDURES Anesthetized dogs were randomly assigned to 4 groups (n = 10/group) with different ventilatory settings: T _V of 8 mL/kg and PEEP of 0 cm H ₂ O (low T _V group), T _V of 8 mL/kg and PEEP of 5 cm H ₂ O (low T _V plus PEEP group), T _V of 15 mL/kg and PEEP of 0 cm H ₂ O (high T _V group), or T _V of 15 mL/kg and PEEP of 5 cm H ₂ O (high T _V plus PEEP group). Expired CO ₂ and respiratory rate were titrated on the basis of a predetermined stepwise protocol. Gas exchange, respiratory mechanics, and pulmonary aeration were evaluated by means of CT 30 minutes after starting mechanical ventilation at the assigned setting.

RESULTS Partial pressures of arterial and expired CO ₂ were higher in the low T _V and low T _V plus PEEP groups than in the high T _V and high T _V plus PEEP groups. Peak and plateau airway pressures were higher in the PEEP group than in the other groups. Static lung compliance was higher in the high T _V plus PEEP group than in the low T _V group. Relative percentages of atelectatic and poorly aerated lung were lower in the high T _V plus PEEP group than in the other groups. Oxygenation was similar among groups.

CONCLUSIONS AND CLINICAL RELEVANCE Differences in T _V and PEEP application during mechanical ventilation may affect respiratory function in anesthetized dogs with healthy lungs. Ventilation with a T _V of 15 mL/kg and PEEP of 5 cm H ₂ O significantly improved lung compliance and reduced the amount of atelectatic and poorly aerated lung.