Mechanical ventilation-induced air-space enlargement during experimental pneumonia in piglets

Mechanical ventilation-induced air-space enlargement was investigated in a porcine model of multifocal pneumonia. Following the intrabronchial inocula tion of Escherichia coli, 9 piglets (22 +/- 2 kg) were ventilated with a ti dal volume (VT) Of 15 ml/kg for 43 +/- 15 h. Five noninoculated piglets ven tilated for 60 h with the same VT served as control animals. Following deat h, the lungs were fixed and lung morphometry was assessed. In inoculated an imals, unventilated infected and normally ventilated noninfected pulmonary lobules coexisted. In normally ventilated lung regions (I) emphysema-like l esions were present, (2) mean alveolar area and mean linear intercept were significantly greater in inoculated than in control animals, and (3) the de gree of alveolar distension correlated with the decrease in respiratory com pliance. In unventilated lung areas (I) pseudocysts were frequent, (2) alve olar edema was rare, (3) bronchiolectasis was frequent, (4) mean bronchiola r area was greater in inoculated than in control animals, and (5) the degre e of bronchiolar distension correlated with the increase in inspiratory pla teau pressure. In conclusion, in piglets with severe bronchopneumonia, air- space enlargement rather than pulmonary edema was the major feature of mech anical ventilation-induced lung barotrauma and resembled lesions previously reported in critically ill patients ventilated using high inspiratory pres sures.