Assessment of Differential Pressures in Chest Drainage Systems: Is What You See What You Get?

Dry-suction chest drainage systems are used to achieve proper drainage of the pleural space after cardiothoracic operations. Data on the actual intrapleural pressure during the use of these systems is lacking. The present study was performed to evaluate pressure differences across the circuit using an ex vivo model.

An ex vivo apparatus coupled to a hospital-grade pleural drainage system was devised to provide calibrated levels of suction and air leak. Simultaneous pressure measurements were obtained at the system outlet and the simulated patient entry site. Trials were conducted with increasing levels of water between the patient and drainage modules at various levels of suction and leak pressures. Signals were recorded at 100 Hz and analyzed using two-way ANOVA.

With no obstruction, the drainage system provided precise levels of negative pressure at the patient level (10-40 cm H₂O). Addition of fluid in the drainage tubing caused significant differences in transmitted suction (P < 0.001). With increasing air leakage and fluid volume, the pressure differential between the system and patient increased significantly (1.14 to 36.69 cm H₂O, P < 0.001). In the off-suction setting, increasing levels of obstruction to 22 cm of water led to development of positive intrapleural pressures (2.6 to 11.1 cm H₂O, P < 0.001).

While commercially available chest drainage systems are able to provide predictable levels of suction at the device, intrapleural pressures can be highly variable and depend on complete patency of connecting tubes. Systems capable of modulating the level of suction based on actual intrapleural pressures may enhance recovery after procedures requiring tube thoracotomy.