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

Abstract

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