My dad's creatinine and urea levels are high due to a congestive heart disease. Please help.

Hello doctor,

My father is 42 years of age, and he has a congestive and congenital heart disease by birth. He visited many doctors, but all of them suggested that there is no need for any immediate treatment and that he can live with it. He is now under medications, and he is doing well. The reason I am addressing you is that my father recently found his urea and creatinine to increase a bit, so we consulted a nephrologist. The doctor said that this is because of his heart problem, the blood does not reach his kidneys properly. They think it is because of dehydration and fluid retention, which has caused an increase in the urea level. But from a month, he is feeling extremely drowsy, which he often experiences, as his body retains fluid, but it decreases again through taking medicines such as Lasix. The only issue now, is that his legs and stomach are swollen due to water retention, and he is feeling very drowsy, and he cannot concentrate on his work. How to effectively treat his drowsiness and swelling? Is there any alternate treatment for his condition?