To understand how to troubleshoot a persistent air leak from a chest tube, one must thoroughly understand the entire algorithm describing the creation and subsequent evacuation and treatment of a pneumothorax.

The chest cavity is a rigid structure made so by the bony scaffold of the rib cage, sternum, and thoracic vertebrae. The left and right hemithoraces are usually anatomically distinct cavities under normal circumstances. However, physiologically they are interdependent due to a soft, relatively compliant mediastinum. Normally, each hemithorax is composed of a rigid outer shell (musculoskeletal) lined on the inside with the parietal pleura. The lung is an aerated organ, soft and compliant, the outside of which is lined with the visceral pleura. The space between the pleurae is maintained at a pressure of negative 5cm H₂O. This pressure, in addition to intra-alveolar lubrication and surfactant, allows the lung to remain open and aerated and prevents collapse on itself. Thus, the movement of the diaphragm in a cephalad-caudad direction aided by much smaller, but not insignificant movement of the intercostals muscle brings air into and out of the lungs via the tracheobronchial tree. It is a system that is open to the outside environment but closed to the chest cavity. Violation of any of the barriers of the closed chest cavity results in release of the negative pressure in the pleural space and collapse of the lung. Ongoing leakage of air into the pleural space results in tension pneumothorax when that air is not able to escape. A chest tube that is placed to alleviate this will demonstrate an ongoing air leak in the water-seal chamber.

Air leaks result from disruption of any one part of the sealed chest cavity. Diagnosis of the source of an air leak is simple in the majority of cases and vital to undertaking appropriate action. The best way to think of a chest-tube circuit is to consider everything from the tube to the water seal (the second chamber) an extension of the pleural cavity. A persistent air leak can be caused only by one of three basic mechanisms: patient pathology; tube pathology; or Pleuravac pathology.