A chest tube, also known as a thoracic catheter, is a flexible, hollow tube inserted through the chest wall into the pleural space between the lung and the inner chest wall. The primary function of this device is to drain unwanted substances—specifically air, excess fluid, or blood—that have accumulated in this space. By removing these materials, the chest tube facilitates the re-expansion of a collapsed or partially collapsed lung. The tube is connected to a closed drainage system that manages the evacuation and prevents anything from returning to the chest cavity.
Why Chest Tubes Require Negative Pressure
The lungs rely on naturally occurring negative pressure within the pleural space to remain fully inflated. The two layers of pleura are held together by this negative pressure, similar to two wet glass slides. When conditions like a pneumothorax (air), a hemothorax (blood), or a pleural effusion (excess fluid) occur, this negative pressure is lost or compromised. The accumulation of air or fluid exerts a positive pressure on the lung, causing it to collapse partially or completely. This disruption prevents the lung from properly expanding during inhalation, which impairs the body’s ability to exchange oxygen and carbon dioxide. The chest tube’s goal is to restore the necessary negative pressure environment, allowing the lung to fully re-expand, thereby restoring normal respiratory function.
Continuous Suction as the Primary Method
Chest tube drainage immediately following insertion is most commonly managed with continuous suction in a clinical setting. This continuous application of negative pressure provides a constant, reliable force to evacuate air and fluid quickly from the pleural space. Continuous suction ensures that the pressure gradient consistently favors the removal of substances, preventing them from re-accumulating between drainage cycles. This is particularly important for patients with persistent air leaks. The typical pressure setting used is around -20 centimeters of water (-20 cm H2O), though this can vary. The use of true intermittent suction is generally avoided in initial management because the momentary cessation of negative pressure could allow air or fluid to be drawn back into the chest cavity.
Transitioning to Water Seal Drainage
Once the patient’s condition stabilizes and the initial, rapid evacuation of air or fluid is complete, the chest tube system is often transitioned from continuous suction to a water seal. The water seal chamber functions as a simple, effective one-way valve: it allows air and fluid to exit the chest but prevents atmospheric air from being sucked back in. When the system is placed on water seal, no external suction is applied; drainage relies on gravity and the patient’s own breathing dynamics. During this monitoring phase, fluctuations in the water seal column, known as tidaling, are expected and indicate that the tube remains open and connected to the pressure changes in the pleural space. Continuous bubbling in the water seal chamber during this phase, however, typically signals an ongoing air leak from the patient’s lung or the drainage system itself.
How Suction Pressure is Controlled
The continuous negative pressure applied to the chest tube is regulated by the drainage system itself, not simply the wall suction source. This regulation is achieved through one of two main types of drainage systems: wet suction control or dry suction control. Both systems are designed to ensure the continuous pressure remains stable at the prescribed setting.
Wet Suction Control Systems
Wet suction control systems use a column of water to regulate the negative pressure. The level of sterile water in the suction control chamber determines the exact suction level applied to the chest, typically set at -20 cm H2O. When the system is connected to a wall suction source, it causes a constant, gentle bubbling in this water column, which visually confirms that the continuous suction is active and operating at the desired pressure.
Dry Suction Control Systems
Dry suction control systems are a more modern alternative that use a mechanical regulator or dial to set the suction level. These systems are often quieter than their wet counterparts because they do not rely on a constantly bubbling water column for pressure regulation. A visible indicator, such as an orange bellows or a flow check window, confirms that the set continuous negative pressure is being delivered to the patient’s chest tube system.