atelectatic

Pneumothorax ex vacuo is a rare type of pneumothorax which forms adjacent to an atelectatic lobe.

During positive pressure ventilation, atelectatic regions will inflate, however the alveoli will be unstable and will collapse during the expiratory phase of the breath(atelectrauma).

Radiographically, pneumothorax ex vacuo is suggested when an atelectatic lobe or lung, particularly right upper lobe atelectasis, is surrounded by a focal pneumothorax.

This can be explained by the changes in ARDS with time, as the lung evolves from a wet, heavy, atelectatic lung to a brittle fibrotic lung [ 12].

When loss of aeration has a focal distribution (atelectatic lower lobes coexisting with aerated upper lobes), a high level of PEEP can cause overinflation of already aerated areas and only partial recruitment of atelectatic areas.

There are normal alveoli which are always inflated and engaging in gas exchange, flooded alveoli which can never, under any ventilatory regime, be used for gas exchange, and atelectatic or partially flooded alveoli that can be "recruited" to participate in gas exchange under certain ventilatory regimens.