A 50-year-old man with muscle-invasive bladder cancer was scheduled for a robotic radical cystectomy. Four hours into the surgery, his electrocardiogram showed rhythm disturbances. Arterial blood gas analysis showed a serum potassium concentration of 6.6 mEq/L. Hyperkalemia was managed immediately with intravenous 10% calcium gluconate, insulin, and glucose administrations, and levosalbutamol was administered through the tracheal tube. Subsequently, normal sinus rhythm returned. The procedure was completed after conversion to an open surgery. The postoperative serum potassium concentration was reduced to 4.6 mEq/L, and the patient was extubated. The remainder of his hospital stay was uneventful.