A chest tube, also known as a thoracostomy tube, is a flexible catheter inserted into the pleural space, the area between the lungs and the chest wall. The primary function of this tube is to drain unwanted substances, such as air (pneumothorax), excess fluid (pleural effusion), or blood (hemothorax), from this space. By removing these materials, the chest tube helps restore the normal negative pressure that allows the lungs to expand fully. The presence of an air leak indicates that air is continuing to escape from the lung or the surrounding system, which complicates the goal of full lung re-expansion.
The Mechanics of a Chest Tube Air Leak
The diagnosis of an air leak relies on the chest drainage system, specifically the water seal chamber. This chamber acts as a one-way valve, allowing air to escape from the chest cavity while preventing atmospheric air from re-entering the pleural space. When air travels from the patient’s pleural space through the chest tube and into the water seal chamber, it creates visible bubbling.
This bubbling confirms a continuous connection between the air source and the drainage system. The air leak can originate from the patient’s body (an internal leak) or be a mechanical issue with the equipment (an external or system leak). Determining the precise origin is an initial step in patient care, as it dictates the necessary intervention. A true air leak from the lung indicates that the underlying injury or condition has not yet fully healed.
Causes Originating from the Lung (Internal Leaks)
The most common reason for an air leak originating from the lung is an unresolved pneumothorax, where air continues to escape the lung tissue and enter the pleural cavity. This leakage often occurs following thoracic surgery, trauma, or spontaneous collapse of the lung. The air travels through a defect in the lung surface and is then evacuated by the chest tube.
A more specific cause is a bronchopleural fistula (BPF), an abnormal connection directly between the large airways and the pleural space. This communication results in a large, continuous air leak because the airflow comes from the higher-pressure respiratory system. The presence of a BPF often requires complex medical or surgical intervention to seal the defect.
Alternatively, the leak may arise from smaller, peripheral lung units through an alveolar-pleural fistula. This involves a rupture of the small air sacs (alveoli) on the surface of the lung, allowing air to seep into the pleural space. These smaller leaks are expected to heal spontaneously as the lung tissue recovers.
Underlying patient factors can also predispose an individual to persistent internal leaks. Patients with emphysematous lungs, characterized by fragile, damaged tissue, are at higher risk for sustained air passage. Extensive damage from trauma or complex lung resections can create larger or multiple sites of air escape that take longer to seal completely.
Causes Originating from the Drainage System (External Leaks)
An air leak originating outside the patient’s body is a mechanical problem involving the chest tube equipment or its connections. This type of leak is often caused by atmospheric air being pulled into the system, which then registers as bubbling in the water seal chamber.
The primary sources of external leaks include:
- Loose connections anywhere along the path from the chest tube insertion site to the drainage unit.
- A defect in the drainage unit itself, such as a crack in the plastic casing of the collection or water seal chamber. This breaks the closed system and requires immediate replacement of the unit.
- Improper sealing at the insertion site where the tube enters the chest wall. If the dressing is loose or sutures fail, air can be sucked in around the tube, especially during inspiration.
- Outward migration of the chest tube, exposing the drainage holes (fenestrations) outside the chest wall. This creates a direct path for outside air to enter the system.
How Air Leaks Are Identified and Graded
The presence of an air leak is first identified by observing the water seal chamber, where bubbles indicate air is exiting the chest. The pattern of this bubbling helps distinguish the leak’s origin and size. Bubbling that occurs only during exhalation or with a cough suggests an internal leak from the lung, as these actions temporarily increase pressure within the chest.
Continuous bubbling, however, may signal a large leak from the patient or a leak within the drainage system itself. To differentiate between these two, a trained clinician may momentarily clamp the tube near the insertion site. If the bubbling stops, the leak is internal, originating from the patient’s lung; if the bubbling continues, the leak is external, located within the tubing or the drainage unit.
Air leaks are often quantified using a standardized grading system to track their severity and progress toward healing. One common method, the Cerfolio classification, grades the leak based on the timing and consistency of the bubbling. A Grade 1 leak is minimal, only visible during a forceful cough, while a Grade 4 leak is continuous throughout both inspiration and expiration, indicating a large or high-flow defect. This objective grading allows medical staff to monitor the lung’s recovery and determine when the chest tube can be safely removed.