Water Seal Drainage System for Pleural Effusion Tapping

Rationale for Water Seal Drainage System

The British Thoracic Society recommends that all chest tubes should be connected to a unidirectional flow drainage system, such as an underwater seal bottle, which must be kept below the level of the patient's chest at all times to prevent backflow 1, 2
The underwater seal bottle has a side vent which either allows escape of air or can be connected to a suction pump, and the system prevents backflow of air into the pleural space, which could lead to pneumothorax or tension pneumothorax 1, 2, 3
The respiratory swing in the fluid level within the chest tube is useful for assessing tube patency and confirms the position of the tube in the pleural cavity 2

The water seal bottle must be kept below the level of the patient's chest at all times to prevent backflow, and the bottle must be kept upright with adequate water placed in the system to cover the end of the tube 2, 4, 5
Daily reassessment of the amount of drainage/bubbling and the presence of respiratory swing should be documented 5

The British Thoracic Society recommends that drainage should be limited to 10 ml/kg initially, after which the drain should be clamped for 1 hour, and in adults, no more than 1-1.5 liters should be drained at one time or drainage slowed to about 500 ml/hour to prevent re-expansion pulmonary edema (RPO) 3, 6, 7
These limitations help prevent RPO, a rare but potentially serious complication 7

Suction is usually unnecessary for pleural drainage, but if applied, a high volume, low pressure system is recommended, and if suction is used, it should be done via the underwater seal at a pressure of 5–10 cm H₂O 1, 7
Low pressure suction means the drain is less likely to become blocked with debris sucked into the lumen 1

A bubbling chest drain should never be clamped due to risk of tension pneumothorax, and a clamped drain should be immediately unclamped if a patient complains of breathlessness or chest pain 3, 5

Re-expansion pulmonary edema from rapid drainage of large effusions is a potential complication, and tension pneumothorax can occur if a bubbling drain is clamped 3, 7
Drain blockage, which should be addressed by checking for kinking and flushing with normal saline, is another potential complication 5, 6

Patients should be managed on wards familiar with chest tubes by staff trained in chest drain management, and patients should be educated to keep the underwater seal bottle below the level of their chest and report problems 5
If the drain abruptly stops draining fluid, check for obstruction by flushing with normal saline, and the drain should be removed once there is clinical resolution, not necessarily waiting for complete cessation of drainage 5, 6