Its safe for 80 years old patient to have kidney transplant while in comma?

Not safe at any age: Kidney transplants are only performed for people who are in very stable medical conditions. Dialysis is used to replace kidney function for people in comas or other types of emergent circumstances. If they survive, they are carefully evaluated + educated as transplant candidates. At any age, the patient must be expected to "survive + thrive" the txp long enough to justify the use of the kidney.

Poorly worded Q: I am not sure what you mean by "while in coma". Most kidney transplant programs will consider "elderly" patients to be a high-risk for renal transplantation. A lot depends on how healthy and functional you are rather than what your chronological age is.