26th June 2023

A 73-year-old man is on the ward recovering from colorectal surgery. It was thought that he might have had an anastomotic leak

A 73-year-old man is on the ward recovering from colorectal surgery. It was thought that he might have had an anastomotic leak earlier in the admission, but this was ruled out following a reassuring CT scan three days ago, and he has since been asymptomatic.

Over the past day, it has been noted that his urine output has been tailing off. His serum creatinine level has increased to 201 μmol/L from 100 μmol/L on admission and his urea has increased to 12 mmol/L from 5 mmol/L. The small amounts of urine that have been produced are dilute at 300 mOsmol/kg with a raised urine sodium 45 mmol/L.

Which of the following is the most likely diagnosis?