A chest tube is a flexible, hollow device inserted into the chest cavity to serve as a drain. Its primary function is to remove unwanted substances—air, fluid, or blood—from the space surrounding the lungs, known as the pleural space. This intervention is necessary because the presence of these materials prevents the lung from fully expanding, which severely compromises breathing. The goal of the chest tube system is to restore the natural pressure mechanics within the chest to allow the collapsed or compressed lung tissue to re-inflate.
Conditions Requiring Chest Tube Placement
The need for a chest tube arises from medical conditions that compromise the pleural space, leading to lung collapse or compression. One of the most common reasons is a pneumothorax, which is the accumulation of air within the pleural space. This air can enter due to trauma, such as a rib fracture puncturing the lung, or spontaneously from a weakened area of the lung tissue.
Another significant condition is a hemothorax, which involves the collection of blood in the pleural cavity, often following blunt or penetrating trauma to the chest. Blood is heavy and can quickly compress the lung tissue, requiring drainage to allow for re-expansion and prevent complications like infection. A pleural effusion involves the buildup of excess fluid, which may be a watery substance or pus, sometimes related to infections, heart failure, or certain malignancies.
The size and clinical impact of these collections determine whether a tube is needed, as small, stable collections may resolve on their own. However, larger or rapidly accumulating materials necessitate immediate drainage to alleviate pressure on the heart and lungs. The placement of the tube is specifically located to drain the material, with tubes for air often placed higher in the chest and those for fluid placed lower due to gravity.
Restoring Negative Pressure: The Underlying Physics
The mechanism of normal breathing relies on a delicate pressure balance within the chest cavity. The lungs are encased in a thin, double-layered membrane called the pleura, creating a potential space between the lung surface and the inner chest wall known as the pleural space. This space contains a small amount of fluid that allows the two pleural layers to slide smoothly past one another.
The pressure inside this pleural space, known as the intrapleural pressure, is naturally sub-atmospheric. This means it is consistently lower than the pressure inside the lungs and the atmospheric pressure outside the body. This negative pressure acts like a continuous suction, holding the lung tissue against the chest wall, which keeps the lungs inflated. When the chest wall expands during inhalation, this negative pressure increases, pulling the lung outward and allowing air to rush in.
When air or fluid enters the pleural space, this negative pressure gradient is destroyed. The pressure equilibrates with the atmosphere or becomes positive relative to the lung, which causes the lung’s natural elasticity to make it recoil and collapse. The chest tube’s primary physical purpose is to remove the excess material, re-establish the necessary vacuum, and restore the pressure difference that holds the lung open against the chest wall.
How the Drainage System Functions
The chest tube is connected to a closed drainage system, which is a specialized apparatus designed to manage the flow of material and regulate the pressure. This system is typically composed of three distinct chambers that work in sequence to achieve the goal of lung re-expansion.
Collection Chamber
The first point of entry for drainage from the patient is the collection chamber, which acts as a reservoir for removed air, blood, or fluid. The collection chamber is calibrated, allowing clinicians to accurately measure the volume and rate of drainage over time, which indicates the patient’s recovery progress.
Water Seal Chamber
Following the collection chamber, the system incorporates the water seal chamber, which is the most mechanically important component. This chamber contains sterile water, usually filled to a specific level, which functions as a one-way valve based on hydrostatic pressure. Air and fluid can exit the chest through the tube and bubble out through the water, but the water column prevents atmospheric air from being sucked back into the pleural space, which would cause the lung to collapse again.
The movement of water in this chamber, known as tidaling, indicates that the system is patent and reflects the pressure changes associated with the patient’s breathing. Bubbling in the water seal chamber signals that air is actively leaving the patient’s chest cavity, a phenomenon that stops once the air leak has resolved and the lung is fully sealed.
Suction Control Chamber
In many cases, the drainage system also includes a suction control chamber, which applies a regulated amount of negative pressure to hasten the removal of air and fluid. In a wet suction system, the level of water in this third chamber dictates the maximum amount of suction applied to the chest, typically set around -20 cm H2O for adults. The height of the water column, not the wall suction setting, is what determines the pressure limit, acting as a safety relief valve.
Dry suction systems achieve the same regulated pressure using a mechanical dial or regulator rather than a water column, offering a more convenient alternative. Regardless of the system type, the combination of the three chambers creates a safe, closed pathway that uses the principles of pressure and gravity to drain the pleural space and restore the negative pressure dynamics necessary for the lung to fully re-inflate.