Pulmonary effects of body position, PEEP, and surfactant depletion in dogs

The influence of position (sphinx, lateral, supine), surfactant depletion, and different positive end‐expiratory pressure (PEEP) on functional residual capacity (FRC), series dead space (V_dS) and compliance of the respiratory system (C_rs) were evaluated in five dogs. Ventilation homogeneity as measured by an index (multiple breath alveolar mixing efficiency), oxygenation, and cardiovascular hemodynamics were additionally examined. The dogs were anesthetized with halothane, paralyzed, and mechanically ventilated. FRC and V_dS were found to be notably large in dogs, 45 ± 8 ml/kg and 6 ± 1 ml/kg, respectively. FRC and ventilation homogeneity were improved in the sphinx position (prone position with upright head). Surfactant depletion by lung lavage with 37±C saline caused an immediate and stable decrease in FRC, C_rs, and oxygenation (P<0.05, respectively) for about 5 h without marked effects on the circulatory system. FRC and V_dS increased with increasing PEEP. At the highest PEEP, 10 cmH₂O (1 kPa), C_rs decreased (P<0.05) and ventilation became more uneven, indicating alveolar overdistension.