PURPOSE: When patients with ARDS or interstitial lung disease develop a pneumothorax, initial insertion of a thoracostomy tube with suction to the customary 20 cmH2O often fails to reexpand the lung. Potential mechanisms for the lack of expansion include: a)lung elastance exceeds the ability of −20 cmH2O pleural pressure to give complete expansion, or b)persistent air leak exceeds the airflow capacity of the thoracostomy tube, such that −20 cmH2O is not achieved in the pleural space. We tested the ability of thoracostomy tubes of various sizes to generate intrapleural pressure changes at various levels of assumed air leak.
METHODS: We designed a chamber to simulate the volume of one hemithorax of a 70 kg human of average height. The airtight chamber allowed insertion of thoracostomy tubes of multiple sizes. Negative pressure was provided by a standard chest drainage unit attached to wall suction and regulated at −20 cmH2O. We tested tubes sized 12 Fr to 32 Fr. Airflow was adjusted in increments via an inlet valve from 0 flow to the flow at which the chest tube failed to generate any negative pressure in the chamber.
RESULTS: Results for suction at −20 cmH2O are presented in Table 1 as F15, F10, and F0, the air leaks at which intrapleural pressure rose to −15 cmH2O, −10 cmH2O, 0 cmH2O, respectively.
CONCLUSION: Small thoracostomy tubes can result in pleural pressures that are less negative than the set value when significant, but realistic air leaks are present; pneumothorax could persist due to insufficient evacuation of air from the pleural space. However, larger tubes appear to accomodate flow from even very large air leaks, suggesting that the mechanism of persistent pneumothorax in this setting may be more closely related to increased lung elastance.
CLINICAL IMPLICATIONS: Chest tubes <= 20 Fr should be avoided in the setting of increased lung elastance with pneumothorax. Further studies are needed to determine the logically appropriate approach when pneumothorax does not respond to insertion of a large tube.
DISCLOSURE: Robert Evangelidis, None.