Dynamics of Recruitment and Collapse of the Lung in Models of ARDS

Abstract

In acute respiratory failure, mechanical ventilation is usually required in order to restore an acceptable gas exchange and to relieve the patient from the increased work of breathing. However, there is evidence from experimental studies that mechanical ventilation itself can induce lung damage by overdistension and repeated opening and closing of alveolar units [1, 2]. Mechanical ventilation may thus be a contributing factor to lung function deterioration during the course of ARDS and this concern prompted the recommendation of a consensus conference on mechanical ventilation to limit the end-inspiratory plateau pressure to 35–45 cm H₂O [3]. Consequently, pressure-controlled ventilation (PCV) has gained widespread popularity in order to limit the end-inspiratory airway pressure. If oxygenation is not acceptable, one may improve gas exchange by either increasing PEEP or extending the inspiratory time interval. Both manoeuvres increase the mean airway pressure, which is a major determinant of oxygenation in acute lung injury [4]. In order to optimise PCV, it is desirable to know the time course of lung collapse during expiration, so that an expiratory time can be chosen that minimises lung collapse, and still allows the lung to expire. During inspiration, complete reopening of collapsed lung tissue should ideally be accomplished with an inspiratory time interval as short as possible in order to reduce the risk of barotrauma.