If someone went for dialysis during Ramadhān, then one has to remember that this only cleans the blood, flushes the kidneys and nothing reaches the stomach or the brain. Therefore, dialysis itself will not break the fast.

However, if one consumed some food or drink after dialysis, the fast will break.

أحكام ص 239

If the kidney patient struggles to fast on the day of dialysis, he could leave that day’s fast and fast on the other days. Then, when Ramadhān finishes, he could make up for the days missed. If he was old and so ill that he was unable to make up for the missed ones, he could give Fidyā.

Extracted from A Gift for Ramadhan, Page 69.

A Gift For Ramadhan – New 3rd Revised Edition