Types of effusion. Pleural effusion is fluid in the space between lungs/chest well. The next step is to ask what kind of fluid is it . 2 types generally are 1: transudative (clear) 2: exudative (pus like). If needed, the fluid can be drained to make this distinction. In terms of common things, a simple pneumonia can cause an effusion. Congestive heart failure can do that from fluid overload. Many possibilties.