A 75-year-old male with a 3-year history of diabetic nephropathy presents with paroxysmal nocturnal dyspnea for 1 week. BP 90/50 mmHg, bilateral basilar rales, heart rate 160 bpm with irregular rhythm, bilateral lower extremity edema, BUN 35 mmol/L, creatinine 1210 μmol/L, CO₂ combining power 9 mmol/L. The most appropriate treatment at this stage is: