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Your father is suffering from kidney disease and Chronic Renal Failure
,as creatinine level is 4.9mg% this is the level where he will require Hemodialysis
so formation of AV fistula is prepration for HD later on.
Urine out put is decrrasing that is why fluid and salt are restrictrd.
He should take care of diet and take adequate amouunt of fibre in diet to avoid constipation
and you can request treating Physician to give a prescription of laxative which will help him,
Once his Kidney function improves he can plan to undergo angiography