A 47-year-old man is admitted to the medical ICU with severe sepsis, multi-lobar pneumonia, and acute respiratory distress syndrome. He developed oliguric acute kidney injury on hospital day 3; he has produced only 240 mL of urine over the past 24 hours despite adequate intravenous hydration. He is mechanically ventilated and requires 80% FIO2. Medical history is unremarkable, and current medications are piperacillin/tazobactam, vancomycin, norepinephrine, vasopressin and propofol infusions, and a proton pump inhibitor.

On physical examination the patient is intubated and sedated. Temperature is 38.5 °C (101.3 °F), blood pressure is 95/60 mm Hg, and pulse rate is 130/min. Estimated central venous pressure is 14 cm H2O. There is no rash. Generalized anasarca is noted. Examination of the chest reveals coarse breath sounds and inspiratory crackles throughout both lungs.

Laboratory studies:

Blood urea nitrogen

103 mg/dL (36.8 mmol/L)

Creatinine

4.3 mg/dL (380.1 µmol/L)

Electrolytes

Sodium

137 mEq/L (137 mmol/L)

Potassium

6.0 mEq/L (6.0 mmol/L)

Chloride

97 mEq/L (97 mmol/L))

Bicarbonate

16 mEq/L (16 mmol/L)

Phosphorus

7.2 mg/dL (2.33 mmol/L)

Serum pH

7.2

Urinalysis

3+ blood; 0-2 erythrocytes/hpf; multiple granular casts and tubular epithelial cells

Which of the following is the most appropriate treatment for this patient's kidney failure?