Air cysts and bronchiectasis prevail in nondependent areas in severe acute respiratory distress syndrome: A computed tomographic study of ventilator-associated changes

Objective: To investigate prevalence and spatial distribution of air cysts and bronchiectasis associated with mechanical ventilation in patients with severe acute respiratory distress syndrome. Design: Retrospective observational study. Setting: University hospital intensive care division. Subjects: A total of 21 patients with severe acute respiratory distress syndrome requiring prolonged mechanical ventilation and undergoing thoracic computed tomographic scanning. Measurements and Main Results: Lung fields were anatomically divided according to functional bronchial divisions in ten segments on each side. Air cysts, bronchiectasis, and the percentage of normal and abnormal tissue were quantified for each segment and correlated to the duration and variables of mechanical ventilation. Air cysts prevailed in nondependent compared with dependent areas (38% ± 5% vs. 9% ± 3%, respectively; p < .01). With mechanical ventilation longer than 10 days, the odds ratio was 13.1 (95% confidence interval, 1.4-118.7) for air cysts and for bronchiectasis 17.6 (95% confidence interval, 2.8-109.6). The amount of abnormal parenchyma correlated with duration of mechanical ventilation on high end-inspiratory pressure but not with tidal volume or minute ventilation. The presence of pneumothorax was not correlated with ventilation settings but with the amount of consolidated tissue revealed by the computed tomographic scan. Conclusions: These findings suggest predominant ventilator-induced lung damage in better ventilated areas (i.e., nondependent regions). Severity of changes revealed by computed tomographic imaging seems to be associated mainly with the high inspiratory pressures required and the length of mechanical ventilation.