What Causes Pleural Effusion Post Quadruple Bypass Surgery?

Two and a half weeks ago my husband went to emerg because he couldn t get his breath when he closed his eyes to sleep. Even sitting up in a chair this would happen. 8 days later he had a quadruple bypass surgery and has done well except the same symptom has returned. His lungs seem to be filling with water so they put him on and IV and then he pees and he feels better and can sleep. After his surgery home one day it happened again and we went back to emerg. They kept him for a few day on IV and then started him on the pills again. The dose went from 40 to 60. We came home Friiday and it is now Sunday and it happened again. I gave him his water pill to see if that would help. He has peed but only a couple of times. He is uncomfortable of course just having major surgery and does not want to return to the hospital. We have been good about water and salt intake. He has been coughing and has got rid of some congestion in the lungs but not a lot. Could this be the cause? How can we help to get rid of it without going back to the hospital? My husband is 70 and is also diabetic(type 2). He was a smoker but has quit. We thought after the surgery he would be able to breath better and sleep. While in the hospital they did do an echo cardiogram and it was fine. There is some rattling in his chest. If the IV works in the hospital could he have that at home with a nurse coming to us each day for a few days? We do have an apt. with his doctor tomorrow afternoon? Do you have suggestions? Thank you so much in advance. Glenda Finlay