A chest tube is a flexible, hollow tube inserted into the pleural space to drain unwanted air or fluid. This procedure re-establishes the normal negative pressure within the chest cavity, allowing a collapsed lung to fully re-expand. Initially, the tube is connected to a drainage system with suction, which actively pulls air or fluid out, typically at a pressure of \(-10\) to \(-20\) cm \(\text{H}_2\text{O}\). The transition from continuous suction to a water seal setting is a significant step in recovery. This change is a specialized procedure performed by trained medical professionals and serves as a test before the tube is removed entirely.
Understanding the Purpose of Water Seal Trials
The rationale for switching from active suction to a water seal setting is to determine if the patient’s lung can maintain expansion independently. This transition, often called a “Water Seal Trial,” tests the integrity of the pleural space without external assistance. Continuous suction provides a constant pressure gradient, ensuring the removal of air or fluid and promoting lung re-expansion.
The water seal mechanism acts as a one-way valve, allowing residual air or fluid to exit the chest cavity while preventing atmospheric air from re-entering. When the chest tube is placed on a water seal, the lung must rely entirely on the body’s natural negative pressure generated during breathing to remain expanded. This trial simulates the conditions the patient will experience after the chest tube is removed.
A successful trial indicates that any air leak has sealed and that the pleural space can be managed by the body’s own pressure dynamics. The trial duration ranges from four to 24 hours, during which the patient is monitored for respiratory distress or fluid accumulation. Stability suggests the underlying injury has healed sufficiently for safe chest tube removal.
The Procedure for Transitioning the Drainage System
The process of changing the chest tube from suction to water seal involves precise mechanical actions on the drainage unit. Before the switch, the healthcare provider must inform the patient and gather baseline data, including vital signs, air leak status, and fluid output.
To stop the active removal of air, the physical connection to the external wall suction source must be interrupted. This is accomplished by turning off the wall vacuum regulator and disconnecting the suction tubing from the drainage device’s designated suction port. For wet suction systems, the gentle bubbling in the suction control chamber will cease when the wall suction is disconnected.
The next step configures the drainage system for passive drainage. If using a dry suction system, the provider confirms the suction dial is set to the “off” or “water seal” position, or opens the high-negativity vent to equalize residual vacuum pressure. This depressurization ensures the water seal chamber correctly reflects the patient’s intrapleural pressure fluctuations without external suction influence.
The exact time of the switch must be noted, and the status of the water seal chamber documented immediately before and after the change. Documentation includes the amount of fluid in the collection chamber and the presence or absence of an air leak, visible as bubbling. The external suction port is left open to the atmosphere.
Monitoring and Assessing the Patient After the Switch
Following the transition to water seal, continuous observation of the patient and the drainage system confirms the trial’s success. The most immediate sign of a persistent air leak is bubbling in the water seal chamber. The cessation or significant reduction of bubbling, especially during coughing, is a primary indicator that the lung surface injury has sealed.
Assessment involves observing “tidaling,” the rise and fall of the fluid level in the water seal chamber corresponding with the patient’s breathing. The fluid level rises with inspiration and falls with expiration, reflecting changes in the negative pressure within the pleural space. If tidaling is absent, it can suggest either that the lung is fully re-expanded or that the chest tube may be blocked or kinked, requiring further investigation.
The patient’s clinical status is monitored closely for signs of respiratory compromise, which indicates a failed trial. This includes frequent checks of vital signs (such as heart rate and oxygen saturation) and assessing for increased shortness of breath or subcutaneous emphysema. If the patient shows distress, the chest tube must be promptly reconnected to suction to assist with lung re-expansion.
A successful water seal trial, usually lasting between four and 24 hours, is defined by the absence of an air leak and minimal fluid drainage. Confirmation by a chest X-ray, demonstrating a fully expanded lung and no recurrence of pneumothorax, is the final step before removal. Minimal drainage is typically considered less than 200–300 milliliters over a 24-hour period.