A 5-year-old boy from a slum in Mumbai presents with persistent bloody diarrhea, fever, and severe abdominal pain for 4 days. His mother reports that his 2-year-old sister developed similar symptoms 1 week earlier. Stool culture yields a gram-negative bacillus that is non-motile, does not ferment lactose, and produces Shiga toxin. The child develops oliguria and thrombocytopenia on day 5 of illness. Which complication is this child at risk for, and what is the most appropriate management?