A chest drainage system, often referred to as a chest tube, is a medical device used to remove air or fluid accumulated in the pleural space surrounding the lungs. This accumulation disrupts the negative pressure needed for the lungs to fully expand, leading to a collapsed or partially collapsed lung. The system relies on gravity and pressure differences to remove substances and restore the lung’s natural state. The water seal chamber is an integrated section of this system, functioning as a safeguard for successful lung re-expansion.
The Primary Function of the Water Seal
The primary purpose of the water seal chamber is to operate as a one-way valve, allowing air and fluid to escape the chest cavity while preventing environmental air from returning. This mechanism maintains the crucial negative pressure within the pleural space. The system is kept below the level of the patient’s chest to promote drainage through gravity, which is enhanced when the patient exhales or coughs.
The water seal works by submerging the end of the drainage tube in a column of sterile water or saline. Air or fluid pushed out of the chest must travel through this liquid barrier to exit the system. The water column creates a seal, preventing atmospheric air from being sucked back into the patient’s chest when they inhale. Without this seal, the pressure balance is compromised, risking a pneumothorax where air re-enters and collapses the lung.
Standard Water Fill Levels
The standard amount of fluid used to create this one-way valve is a column of water measuring approximately 2 centimeters (cm) in height. This 2 cm level is a clinical standard that provides a calculated resistance to air backflow. The measurement is a height of water, which translates directly to a specific amount of pressure, typically expressed as 2 cm H₂O.
This depth is carefully chosen because it is deep enough to effectively seal the system against atmospheric pressure during inhalation. However, it is not so deep that it creates excessive resistance against the patient’s efforts to expel air or fluid from the chest. Manufacturers of modern disposable chest drainage systems include a marked line on the water seal chamber to guide the initial filling with sterile water or saline. While the actual volume of fluid needed may vary slightly between different drainage unit designs, the functional measurement that matters is the 2 cm height of the water column.
Consequences of Incorrect Water Levels
Deviating from the standard 2 cm water level can lead to problems that affect the system’s function and patient safety. If the water level falls too low, the immediate danger is the loss of the water seal. Evaporation can cause the water level to drop, meaning the tip of the tube is no longer adequately submerged.
This breach allows air from the environment to be drawn directly back into the pleural space during inhalation, potentially worsening a collapsed lung. Conversely, if the water level is too high, it increases the resistance the patient’s lungs must overcome to push air out. This excessive resistance can slow down the lung’s re-expansion and cause patient discomfort by making breathing and exhalation more difficult.
Monitoring the Water Seal Chamber
The water seal chamber provides visual confirmation of the system’s function and the patient’s progress through two key indicators: tidaling and bubbling. Tidaling, or oscillation, is the normal fluctuation of the water level that mirrors the patient’s breathing cycle. For a spontaneously breathing patient, the water level rises with inhalation and falls with exhalation, reflecting changing intrathoracic pressure.
The presence of tidaling confirms that the chest tube is properly placed and is not kinked or blocked by a clot. If tidaling stops, it usually signals that the lung has fully re-expanded and sealed the air leak, or it may indicate a blockage in the tubing that requires immediate assessment. Bubbling in the water seal chamber indicates that air is escaping from the patient’s chest. Intermittent bubbling is expected when the patient has a pneumothorax, as air is pushed out with each breath or cough. However, continuous, vigorous bubbling often signals an air leak somewhere in the system—either from the patient’s lung or a loose connection in the drainage unit.