A 72-year-old man is admitted to the ICU for septic shock due to pneumonia. He receives aggressive fluid resuscitation and norepinephrine. Over the first 24 hours, his blood pressure improves and his creatinine decreases from 2.1 mg/dL to 1.7 mg/dL after fluids. On hospital day 2, despite stable mean arterial pressure, his urine output falls to 250 mL over 24 hours. Labs show: BUN 86 mg/dL, creatinine 4.3 mg/dL, potassium 6.2 mEq/L. Urinalysis shows muddy brown granular casts and renal tubular epithelial cell casts. Which of the following best describes the phase and expected clinical issue in this patient?