Passive atelectasis

Last revised by Liz Silverstone on 22 Sep 2024

Passive atelectasis, also known as relaxation atelectasis is due to elastic recoil of the lung when normal negative pleural pressure is reduced or lost due to a pleural collection such as a pneumothorax or pleural effusion.

The clinical presentation would depend on the extent of atelectasis and how quickly it develops. Small and gradually developing areas of atelectasis may be asymptomatic or present as a non-productive cough. Larger areas that develop more quickly can present with hypoxia, respiratory failure, cough, and/or pleuritic chest pain 6.

Physical examination of the lungs may reveal a diminished movement of the affected area, dullness on percussion decreased or absent breath sounds, and ipsilateral tracheal deviation 6.

With a loss of the negative intrapleural pressure there is equalization of intrapleural and intra-alveolar pressures and the lung is said to "relax" due to its normal elastic recoil resulting in lung volume loss 5. In the case of diaphragmatic abnormalities, there is a reduction in downward force to fully expand the lungs resulting in passive atelectasis 5.

Causes of passive atelectasis may be grouped into three main categories 5:

There may not be a significant increase in density from the atelectasis, as perfusion of the affected lung also decreases ref.

  • atelectatic lung may demonstrate marked enhancement, greater than that of skeletal muscle (see case 2)

  • the presence of air bronchograms helps to exclude airway obstruction as a cause

  • as gases are the main constituent of normal lung, loss of aeration can cause profound collapse

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