What to do if i have fluid in the pleural cavity. how would you expect this to affect the process of pulmonary ventilation?

Pleural effusion: Fluid in the pleural cavity causes compression of the lung and reduces your lung capacity, thereby reducing your ventilation capacity. This is important to have checked out and treated. Depending on quantity, this may require draining some fluid for analysis. Treatment depends on cause, needs evaluation. See your doctor for advise.