Closed thoracic drainage, as you can see from the literal meaning of the word, drainage is the draining of material from the chest cavity, whether it is gas or liquid or blood, and it is airtight, that is why it is called closed thoracic drainage, also known as closed thoracic drainage. The reason why it’s important to drain the fluid or gas out of the chest cavity is because in a normal person, the chest cavity, or pleural cavity is between the lungs and the chest wall, and in a normal person this cavity is a potential cavity with only about 30mL or so of lubricating fluid, which is mainly used to keep the lungs and the chest wall from violently rubbing together and causing pain when you take a deep breath. And due to certain reasons, such as trauma or lung cancer involvement, it can lead to the appearance of gas or fluid in the pleural cavity, and at this time the gas and fluid can press on the lungs, so that the lungs don’t have the means to expand fully and effectively. Therefore, a small tube should be put into the pleural cavity to drain out the gas and fluid adequately. The reason why it has to be closed is because only the fluid or gas inside is allowed to drain out, and no outside fluid or air can enter the pleural cavity, so it is called a closed chest drain.