Urine output should be measured and accurately recorded on the fluid balance chart. This should be undertaken as clinically indicated (e.g. hourly in the immediate post‐operative period). Nurses should also monitor and report changes in the character (colour, viscosity or odour) or volume of urine output; for example, oliguria (urine output of less than 0.5 mL/kg/hour for 2 consecutive hours in a catheterized patient) could indicate the patient is hypovolaemic and should be reported to surgical staff immediately (once catheter tubing has been checked to confirm it is not kinked or blocked). If a patient does not have a catheter in situ, it is important that the patient is asked to pass urine into a jug or commode so that the volume of urine can be measured and recorded.

The inability to pass urine post‐operatively is usually caused by a condition called ‘neurogenic bladder’, a type of bladder dysfunction that interferes with the nerve impulses from the brain to the bladder, preventing it from emptying. For patients with no history of difficulty urinating prior to surgery, the problem is often attributed to a combination of risk factors that include abdominal surgery, general anaesthesia, and pain medications and fluids given perioperatively. Signs that a patient is in urinary retention include the patient reporting discomfort, pain, a full bladder and/or inability to urinate despite feeling the urge. A bladder scan can be used to determine the residual volume of urine in the bladder. If encouraging the patient to urinate on several occasions is unsuccessful, then an in/out urinary catheter can be inserted to drain the bladder. No attempts should be made to catheterize the patient without seeking confirmation from the surgical team that this is the appropriate course of action to take.