How a cuff turns a tube into a one-way route
An endotracheal tube passes through the mouth or nose and into the trachea, the windpipe leading to the lungs. The tube creates a path for air, but it does not fill the trachea’s width. Without a seal, some air delivered under pressure could escape through the gap around the tube rather than travel down into the lungs.
Near the tube’s tip is a soft, inflatable balloon called a cuff. Once the tube is positioned, the cuff is inflated so it gently presses against the tracheal wall. That contact limits the space around the tube, helping ventilator breaths follow the tube’s open channel into the lungs.
A seal has to be carefully balanced
The cuff is not meant to clamp the airway shut. It is inflated only enough to reduce leakage while avoiding unnecessary pressure on the trachea’s delicate lining. Too little inflation can allow air to escape; too much pressure can injure tissue. Clinicians therefore monitor the cuff rather than treating it as a simple plug.
The cuff also helps reduce the amount of fluid that can pass from the upper airway down around the tube, though it is not a perfect barrier. Its job is to improve control over airflow and limit bypass—not to make the airway completely sealed against every leak.
That small balloon is what lets a ventilator deliver breaths through a narrow tube with less air slipping past it, while making the seal a pressure-sensitive part of the airway setup.
