Urinary Retention

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Last updated: August 17, 2019
Revisions: 20

Last updated: August 17, 2019
Revisions: 20

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Acute urinary retention (AUR) describes a symptomatic inability to completely empty the bladder.

AUR is a relatively common complication in the post-surgical patient, so a clear understanding of its diagnosis, assessment, and management is important.

Clinical Features

The most common diagnostic signs or symptoms of acute urinary retention are:

  • Little or no urine passed in the post-operative period
  • A sensation of needing to void, without being able to micturate
    • The retention of urine may be painless in patients with previous chronic urinary retention
  • A suprapubic mass that is dull to percussion

Patients presenting with urinary retention should be assessed for any underlying causes. Common causes for acute retention  post-operatively include uncontrolled pain, constipation, infection, or anaesthetic agents* (e.g. spinal or epidural use)

*In the immediate post-operative period, any neurological deficit is usually because the spinal or epidural anaesthetic has not yet worn off, but other more potentially serious neurological causes should be considered.

Risk Factors

There are several risk factors for post-operative urinary retention:

  • Age >50yrs
  • Male gender
  • Previous retention
  • Type of surgery
    • Including pelvic or urological surgery
  • Anaesthetic type (spinal or epidural)
  • Neurological or urological co-morbidities
  • Medication (e.g. antimuscarinics, alpha agonists, opiates)


Together with a thorough clinical assessment, the most important investigation is the ultrasonic bladder scan to identify the post-void residual urine volume*.

Check for any potential underlying reversible causes and that there is adequate pain control. Check the patient has a stable renal function (as worsening renal function may suggest a high-pressure retention that is impacting renal function)

*Most post-void residual volumes should be negligible; patients who were known pre-operatively to be in chronic retention may have what seems to be a large post-void volume, however as long as they can void good volumes with each micturition and the post-void volumes are relatively stable with unaffected renal function, this is often of minimal concern 

Fig 1 - Ultrasound bladder scan, showing an enlarged bladder with urinary retention (yellow arrow). By Massinde Anthony [CC-BY 3.0], from International Journal of Case Reports in Medicine

Figure 1 – Ultrasound bladder scan, showing an enlarged bladder with urinary retention (yellow arrow)


A conservative approach may be taken in many patients; the majority of post-operative urinary retention will resolve spontaneously given time and withdrawal of any causative agents.

In those that do not resolve, any significant retention will require catheterisation (at least overnight). Patients can have their catheter removed shortly after (often termed a Trial Without Catheter (TWOC))

For those that fail their TWOC and re-enter retention, a new catheter should be reinserted and patients for repeat TWOC in 1-2 weeks in the community. Importantly, make sure to re-assess any potential reversible causes why the patient may have failed their TWOC that can be addressed

Key Points

  • Acute urinary retention describes a symptomatic inability to completely empty the bladder
  • Common causes for acute retention post-operatively include uncontrolled pain, constipation, infection, or anaesthetic agents and medication
  • Bladder scan and U&Es are essential tests in any post-operative retention
  • Any acute retention requires catheterisation, to have the catheter removed a few days after, however it is also important to assess for underlying causes of any retention