A 58-year-old man with diabetes mellitus type 2 and hypertension presents to the emergency department with acute onset oliguria (urine output 0.3 mL/kg/hr) for 8 hours. Serum creatinine has risen from baseline 1.2 mg/dL to 2.8 mg/dL. Urinalysis shows muddy brown casts and granular casts. On examination, he is euvolemic with normal JVP. Blood pressure is 148/92 mmHg. He reports no recent nephrotoxic drug exposure. What is the most appropriate immediate next step in management?