a young male patient with rheumatic mitral valve disease underwent a valve replacement surgery.His baseline creatinine is 1.2 mg/dl, and border line cardiac function with ejection fraction of 45% ,the valve was prosthetic valve with bypass procedure for 9 hours.. Everything went smooth without any complications intraoperatively.In the very next day he developed a severe hyperkalemia of 7 meg/l, his creatinine went up to 1.6 mg/dl, with good urine output . He was aggressively diuresed for volume overload with  lasix leading to polyuria and creatnine jumped up to 2.5 mg/dl on the next day,  Despite the polyuria and mild renal impairment on a background of stable hemodynamic status, he developed serum K of 7 Meg/l !!!!.He required  the initiation of CRRT due to  vasopressor dependence.There is no evidence of hemolysis and other electrolytes are within normal.he is on heparin and CPK is 8000.

Is the CRRT indicated in the situation of mild renal impairment and polyuria??

what could be the causes of hyperkalemia?

your response is appreciated