Soru

A $55$-year-old woman is evaluated on postoperative day $4$ following an open low anterior resection for locally advanced rectal cancer. She reports new-onset, constant, right-sided flank pain and mild nausea that began yesterday. Her temperature is $38.1^\circ\text{C}$ ($100.6^\circ\text{F}$), blood pressure is $125/75\text{ mmHg}$, and pulse is $92/\text{min}$. Physical examination reveals a clean midline abdominal incision with normal, active bowel sounds. There is distinct right costovertebral angle tenderness, but no rebound tenderness or guarding. A urethral Foley catheter was removed on postoperative day $2$, and the patient has since been voiding spontaneously with an output of approximately $450\text{ mL}$ every $8$ hours. Laboratory studies show a serum creatinine of $0.9\text{ mg/dL}$ (baseline $0.8\text{ mg/dL}$) and a leukocyte count of $12,500/\mu\text{L}$. Urinalysis shows $2$-$3$ white blood cells/hpf and no bacteria. Which of the following is the most appropriate next step in management?