EFFECT OF DIFFERENT PRESSURE LEVELS ON THE DYNAMICS OF LUNG COLLAPSE AND RECRUITMENT IN OLEIC-ACID-INDUCED LUNG INJURY

The effects of different inspiratory and expiratory airway pressures ( Paw) on the dynamics of lung collapse and recruitment were studied in 14 anesthetized, mechanically ventilated, pigs with oleic-cid-induced lung injury. Repetitive CT scans of the same slice were obtained every 0.8 s during different inspiration and expiration hold procedures. Th e mean lung density and amount of atelectasis were measured in each sc an. Inspiration to a Paw of 15 cm H2O above PEEP resulted in recruitme nt of collapsed lung tissue, mainly within 1.4 s. During expiration lu ng density increased rapidly and at an almost even rate within the fir st 1.4 s, whereas a rapid increase of atelectasis occurred after an in itial delay period of 0.6 s with PEEP = 10 or 15 cm H2O. PEEP of 20 or 25 cm H2O almost prevented lung collapse during expiration. Thus, in order to avoid cyclic alveolar collapse during mechanical ventilation in oleic-acid-induced lung injury, a PEEP level greater than or equal to 20 cmH(2)O or an expiration time less than or equal to 0.6 s is req uired. Long inspiratory time intervals, as used in inverse ratio venti lation, seem to be of minor importance for the recruitment of collapse d lung tissue in this experimental model.