A 78-year-old man is admitted with sepsis secondary to a urinary tract infection. His baseline creatinine is 100 µmol/L. On admission, his creatinine is 180 µmol/L and urea is 22 mmol/L. He is hypotensive (BP 85/50 mmHg) and tachycardic (110 bpm). He is given IV fluids. What is the most likely cause of his acute kidney injury (AKI)?