Airway closure, more harmful than atelectasis in intensive care?

Excerpt

Since the mid-1980s, atelectasis has been demonstrated during anesthesia in lung healthy subjects [1] and in intensive care patients suffering from acute respiratory failure and requiring ventilator support [2]. In the latter case, there are additional causes of airless lung tissues, such as alveolar fluid filling and consolidation. The airless tissue is still perfused, causing a shunt with impairment of the oxygenation of blood. Moreover, cyclic opening and closing of alveolar units may harm the tissue and trigger an inflammatory reaction [3]. This is well known and has been considered a major morphological disturbance in the mechanically ventilated subject. However, there are indirect observations of another morphological disturbance, some airways that are either continuously closed or cyclically opening and closing during the ventilation. This airway closure is a normal phenomenon, although of small magnitude and seldom continuous, in awake, spontaneously breathing healthy subjects. It begins in dependent lung regions and spreads out to include additional airways during the continuing expiration [4]. However, during anesthesia and in acute respiratory failure airway closure is much more marked and may be of similar importance as alveolar airlessness in impeding lung function, and promoting inflammation [5, 6]. …