i used to work on a stepdown unit that had a lot of patients with chest tubes. we had a chest surgeon who used to come around who delighted in grabbing a nurse or two and grilling them about chest tubes and how they functioned. he would embarrass you if you didn't know the answers to his questions. so, i spent some hours in a medical library looking up information on how chest tubes worked and became a bit of an expert on it for my unit, going around inservicing as many nurses as i could. when you have the time to get into a library you should be able to find some very good nursing articles that explain how chest tubes work and the nursing care of them.
lungs work the opposite of other organs. they work by negative pressure. they deflate when a tube is inserted into them, like a balloon that is pierced by a needle. so, a chest tube drainage system will be a closed system because external pressure sucks air (and any drainage gunk) out of them. this is why you will see fluctuation of fluid in the chest drainage tube as the patient breathes. when the patient takes a breath (inspires), fluid from the closed drainage system gets pushed out through the chest tube (blood, pus, excess air in the pleural space), but maintains the integrity of lungs; as the patient breathes out (expires) some of the fluid in the closed drainage system that the chest tube is connected to, the water seal, will be pulled up into the chest tube due to the negative pressure created in the lung. you basically have to understand that concept in caring for and maintaining the tubes. then, there are always complications connected with these tubes that you need to know how to deal with. like all other medical treatments, little problems come along that you have to know how to handle.
this web page from notes on icu nursing (http://www.icufaqs.org/
) may say and explain it a little better: