A 40-year-old male farmer presents with 3 days of irregular fever, headache, low back pain, and blurred vision. Physical exam shows facial and upper chest congestion, conjunctival edema, petechiae, and scattered pin-sized hemorrhages in axillae and back. BP is 90/60 mmHg. Suspected epidemic hemorrhagic fever (febrile phase) due to similar cases in the village. Persistent oliguria for 3 days. Laboratory tests: BUN 60 mmol/L, Cr 602 μmol/L, serum K+ 6.9 mmol/L. The most appropriate management is: