Q. A 75-year-old male was admitted last night through the emergency department for a complicated urinary tract infection. He has been experiencing difficulty with urination for the past year, and his urinary symptoms have been progressively worsening. Over the past week, the patient has noticed that he has been feeling more tired than usual and has a decreased appetite. His home medications are tamsulosin, furosemide, and lisinopril. On presentation to the emergency department, the patient was found to have turbid, yellow urine which was positive for blood, protein, nitrites, and leukocyte esterase. Additionally, red and white blood cells, as well as bacteria were noted on microscopy. The patient was febrile and believed to be volume depleted, and was subsequently admitted for IV ceftriaxone and hydration. Today, the patient’s condition has deteriorated. Despite receiving 2 L of fluid since admission, he has not produced any urine. On physical examination, his temperature is 38.5 degrees Celsius (101.3 degrees Fahrenheit), blood pressure 170/100 mm Hg, heart rate 100/min, respiratory rate 20/min, and his oxygen saturation is 92 percent on room air. His cardiopulmonary examination is unremarkable. Abdominal assessment reveals significant suprapubic abdominal tenderness, and an enlarged, tender bladder. You perform a digital rectal examination and note a warm, tender, boggy, enlarged prostate. You order an arterial blood gas and review the patient’s labs. Laboratory results: pH: 7.33 PaO2: 80 mmHg PaCO2: 38 mmHg HCO3: 24 mmol/L Leukocyte count: 14,000/mm3 Hemoglobin: 10 g/dL Hematocrit: 35 percent Platelet count: 95,000/mm3 Serum creatinine: 4.5 mg/dL Blood urea nitrogen: 50 mg/dL Based on the information you have at this point in time, what is the most likely etiology of this patient’s deteriorating condition?