35-year-old women has 5 day history of fever, malaise, headache, and spontaneous bruising. On examination, temp 38.5 C, HR 110/min, BP 150/89 mmHg, and RR 18/min. Cardiopulmonary and neurological examination is normal. Her initial investigation show hemoglobin 9 g/dl, WBC 4600/ul. Plt count 55,000/ul, creatinine 3.5 mg/dl, BUN 52 mg/dl, and the peripheral blood film shows fragmented red blood cells. Which of the following is the most appropriate lifesaving treatment?