Review Question - QID 212568

A 67-year-old man is brought to the emergency department when he was found obtunded at the homeless shelter. The patient is currently not responsive and smells of alcohol. The patient has a past medical history of alcohol use, IV drug use, and hepatitis C. His temperature is 99°F (37.2°C), blood pressure is 95/65 mmHg, pulse is 95/min, respirations are 13/min, and oxygen saturation is 95% on room air. The patient is started on IV fluids, and his pulse decreases to 70/min. On physical exam, the patient has an abdominal exam notable for distension and a positive fluid wave. The patient displays mild yellow discoloration of his skin. The patient has notable poor dentition and poor hygiene overall. A systolic murmur is heard along the left sternal border on cardiac exam. Pulmonary exam is notable for mild bibasilar crackles. Laboratory values are ordered, and return as below:

Hemoglobin: 10 g/dL
Hematocrit: 32%
Leukocyte count: 7,500 cells/mm^3 with normal differential
Platelet count: 227,000/mm^3

Serum:
Na+: 125 mEq/L
Cl-: 100 mEq/L
K+: 5.0 mEq/L
HCO3-: 24 mEq/L
BUN: 51 mg/dL
Glucose: 89 mg/dL
Creatinine: 2.2 mg/dL
Ca2+: 10.0 mg/dL
AST: 22 U/L
ALT: 19 U/L

Urine:
Color: Amber
Nitrites: Negative
Sodium: 12 mmol/24 hours
Red blood cells: 0/hpf

Over the next 24 hours, the patient produces very little urine. Which of the following best explains this patient’s renal findings?