Why Patients Should Cough During Chest Drain Examination
Asking patients to cough during chest drain examination allows clinicians to assess for air leaks in the pleural space and verify proper drain function by observing for bubbling in the water seal chamber, which indicates whether the pneumothorax is resolving or if there is a persistent air leak from the lung. 1
Primary Purpose: Air Leak Detection
When examining a functioning chest drain, having the patient cough serves as a critical diagnostic maneuver:
Coughing generates sudden increases in intrathoracic pressure that forces any residual air in the pleural space through the chest drain system, making air leaks visible as bubbling in the water seal chamber 1, 2
The pressure changes during cough are substantial - voluntary coughs generate significant intra-thoracic pressure increases that can mobilize trapped air pockets that might not be evident during quiet breathing 3
This maneuver helps distinguish between resolved and persistent pneumothorax - if bubbling occurs only with cough but not during quiet breathing, this suggests a small residual air leak that may seal spontaneously; continuous bubbling suggests a larger persistent leak requiring continued drainage 2
Assessment of Drain Patency and Position
The cough test also verifies mechanical drain function:
Observing fluid oscillation (tidaling) in the tubing during cough confirms the drain is patent and properly positioned within the pleural space 1, 2
Absence of any response to coughing may indicate drain blockage, malposition, or complete lung re-expansion requiring further investigation 2
Clinical Decision-Making for Drain Removal
This assessment directly impacts management decisions:
Chest drains are typically removed when there is no air leak (no bubbling even with cough), the lung has re-expanded, and drainage output is minimal 1
The cough test is performed as part of the pre-removal assessment to ensure no occult air leak exists that might cause pneumothorax recurrence after drain removal 1, 2
Common Pitfalls to Avoid
Do not rely solely on quiet breathing to assess for air leaks - small leaks may only become apparent with the increased intrathoracic pressure generated by coughing 2, 3
Ensure the water seal chamber is at the correct level and functioning properly before interpreting the cough test, as equipment malfunction can give false results 2
Remember that the absence of bubbling with cough does not guarantee complete resolution if the drain is blocked or malpositioned - correlate with clinical examination and imaging 1, 2