• Mechanical ventilation expands the lungs and chest wall by pressurizing the airway during inflation. The stretched lungs and chest wall develop recoil tension that drives expiration.
  • Positive pressure developed in the pleural space may have adverse effects on venous return, cardiac output and dead space creation.
  • Stretching the lung refreshes the alveolar gas, but excessive stretch subjects the tissue to tensile stresses which may exceed the structural tolerance limits of this delicate membrane.
  • Disrupted alveolar membranes allow gas to seep into the interstitial compartment, where it collects, and migrates toward regions with lower tissue pressures.
  • Interstitial, mediastinal, and subcutaneous emphysema are frequently the consequences.  Less commonly, pneumoperitoneum, pneumothorax, and tension cysts may form.
  • Rarely, a communication between the high pressure gas pocket and the pulmonary veins generates systemic gas emboli.

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