Background: Prolonged air leakage is common after lung resection. We observed that during deep inspiration some patients were able to empty the water-seal of commercial chest drainage systems and retract air back into the chest tube, which subsequently escaped during the following expiration, mimicking "true" air leakage. This led us to perform in vitro and in vivo pressure measurements in chest tube systems and investigate possible relationships with "false" air.
Methods: Commercially available one- and three-chamber drainage systems were used as models for large and small water-seals, respectively. Digital pressure measurements were performed in vitro and in ten selected patients with clinical suspicion of reverse airflow.
Results: Repeated measurements in the laboratory demonstrated that in three-chamber chest drainage systems with small water-seals a negative pressure below -30.4 cmH(2)O led to emptying of the water-seal with retrograde flow of air. Retrograde airflow was not possible in one-chamber chest drainage systems. In vivo measurements demonstrated that six of ten highly selected patients were able to create negative pressures below -30.4 cmH(2)O during deep inspiration.
Conclusion: During deep inspiration some patients are able to create negative pressure large enough to empty small water-seals in commercial chest drainage systems and retract air back into the chest tube. This excess air escapes during the following expiration and may mislead interpretation of continued air leakage even when there is none, subsequently resulting in prolonged and unnecessary chest tube drainage. Any surgeon who treats patients with chest tubes should be aware of this phenomenon.