When suction is applied to a chest tube, it is typically continuous, not intermittent. The standard approach uses a low-pressure setting, usually between -10 and -20 cmH2O, running steadily to maintain a consistent pressure difference between the chest cavity and the outside. That said, many patients don’t need suction at all. A large number of chest tubes drain effectively using gravity and a water seal alone, with suction reserved for specific situations.
Why Suction Is Continuous When Used
The goal of chest tube suction is to keep gentle, steady negative pressure inside the pleural space, the thin gap between your lungs and chest wall. This pressure difference helps pull trapped air or fluid out through the tube and encourages the lung to re-expand against the chest wall. Cycling suction on and off would allow pressure to fluctuate, potentially letting air or fluid re-accumulate between cycles. Continuous low pressure avoids that problem.
There are two main types of drainage systems that deliver this continuous suction. A wet suction system controls the pressure using a column of water, typically set at -20 cmH2O for adults. A dry suction system uses a mechanical regulator to maintain the target pressure and adjusts automatically in response to air leaks, keeping suction more consistent. Both are designed to run continuously once connected to a suction source.
When Suction Isn’t Needed at All
A chest tube connected to a water seal (essentially a one-way valve that lets air and fluid escape but prevents anything from flowing back in) often works without any suction. Basic physics explains why: as long as the chest cavity is a closed system, the natural pressure inside is enough to push fluid outward, especially when coughing creates short bursts of higher pressure. The British Thoracic Society guidelines for spontaneous pneumothorax and chest drain insertion do not recommend routine use of suction.
Suction becomes more important in open systems, where there’s no meaningful pressure difference to drive drainage on its own. A large air leak from a pneumothorax or an open surgical space in the chest after an operation are common examples. In those situations, the chest cavity has essentially equalized with atmospheric pressure, so an external source of suction is needed to pull air or fluid out.
Suction Can Sometimes Do More Harm Than Good
There’s a common assumption that stronger or longer suction leads to better drainage, but research tells a different story. Suction can actually prolong air leaks by pulling air through a small hole in the lung that would otherwise seal on its own. Excessive suction also risks damaging tissue, increasing patient discomfort, and extending hospital stays because the air leak never gets a chance to close.
A retrospective study comparing water seal drainage to low suction after lung surgery found that the water seal group had shorter air leak duration (2 days versus 3 days) and shorter overall drainage time (3 days versus 5 days). At one week after surgery, 94.9% of the water seal group had stopped leaking air, compared to 80.7% of the low suction group. The water seal group also needed fewer escalations to higher suction for complications like air collecting under the skin.
This is why the current trend in thoracic medicine leans toward using suction selectively rather than as a default. When it is used, keeping the pressure in the -10 to -20 cmH2O range reduces the risk of tissue damage and prevents the suction from perpetuating the very leak it’s trying to resolve.
How Patients Transition Off Suction
The typical progression is from continuous wall suction to water seal, then to tube removal. The transition usually happens once an air leak has resolved, confirmed by chest X-rays taken before and after switching. For fluid drainage, a common threshold is less than 150 milliliters of output over 24 hours. Once the tube is on water seal and the lung stays expanded on imaging, removal is the next step.
This stepwise approach is essentially a test: if the lung holds its position without suction, the tube has done its job. If the lung collapses again after switching to water seal, suction may be restarted. The process can take anywhere from a day to over a week depending on how quickly the underlying problem resolves.
Pneumothorax vs. Fluid Drainage
Whether the tube is draining air or fluid affects how suction is used. For a simple pleural effusion (fluid buildup), gravity and the body’s own pressure are often enough. The chest is still a closed system, and natural hydrostatic pressure pushes fluid toward the drain. Suction may speed things up slightly but isn’t always necessary.
For a pneumothorax, the decision depends on the size of the air leak. A small, self-contained pneumothorax may resolve with water seal alone. A large air leak, where air is continuously escaping from the lung surface, often requires continuous suction to keep the lung inflated against the chest wall. The idea is that holding the two layers of the pleural space together promotes healing of the leak, though the evidence supporting this is not definitive.
After chest surgery, suction is commonly applied in the early postoperative period because the surgical site is essentially an open system. But as the evidence above suggests, earlier transition to water seal may actually produce better outcomes in many surgical patients.