Respiratory effects of low versus high tidal volume with or without positive end-expiratory pressure in anesthetized dogs with healthy lungs

OBJECTIVE To evaluate the impact of 2 tidal volumes (TVs) 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: TVof 8 mL/kg and PEEP of 0 cm H2O (low TVgroup), TVof 8 mL/kg and PEEP of 5 cm H2O (low TVplus PEEP group), TVof 15 mL/kg and PEEP of 0 cm H2O (high TVgroup), or TVof 15 mL/kg and PEEP of 5 cm H2O (high TVplus PEEP group). Expired CO2and 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 CO2were higher in the low TVand low TVplus PEEP groups than in the high TVand high TVplus 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 TVplus PEEP group than in the low TVgroup. Relative percentages of atelectatic and poorly aerated lung were lower in the high TVplus PEEP group than in the other groups. Oxygenation was similar among groups. CONCLUSIONS AND CLINICAL RELEVANCE Differences in TVand PEEP application during mechanical ventilation may affect respiratory function in anesthetized dogs with healthy lungs. Ventilation with a TVof 15 mL/kg and PEEP of 5 cm H2O significantly improved lung compliance and reduced the amount of atelectatic and poorly aerated lung.