Q. A previously healthy 4-year-old boy is brought to the emergency department with a 2-day history of bloody diarrhea, abdominal pain, and decreased urine output. His mother reports that he had a fever and diarrhea following a recent family picnic a few days ago. His temperature is 100°F (37.8°C), heart rate is 100/min, respiratory rate is 14/minute, and blood pressure is 128/85 mm of Hg. On examination, the child appears pale, and lethargic and has periorbital edema. Laboratory findings are shown below. The peripheral blood smear shows abundant schistocytes and helmet cells. Coombs test is negative and stool culture is negative for enteric pathogens. What is the most appropriate next step in the management of this patient's condition?