My Father Has A Great Deal Of Swelling In His

My father has a great deal of swelling in his feet and now some in his legs. He has a number of problems and his doctor believes weak veins, poor nutrition, chronic kidney disease, congestive heart failure (says his heart function is "decent") are the main causes. Dad still isn't taking it very seriously. The home health nurse said his feet were at 18. I don't know what that means other than they are very, very swollen. What can happen to his feet if he continues to keep his feet down22 hours a day?