A 76-year-old woman is admitted with vomiting and diarrhoea for 3 days. She is taking Ramipril and Ibuprofen regularly. Her creatinine has risen from 90 µmol/L (baseline) to 240 µmol/L and urea is 18 mmol/L. She is hypotensive and clinically dehydrated. What is the most appropriate immediate management?