Urinary Catheters

Urinary catheters are inserted into the bladder to passively drain urine. The urine drains through a tube into a catheter bag. They may be used short term or long term, depending on the indication.

When urinary catheters are left in, a balloon on the end of the catheter bladder is inflated inside the bladder with sterile water (usually 10mls), preventing it from falling out.



The reasons for inserting a urinary catheter include:

  • Urinary retention due to a lower urinary tract obstruction (e.g., enlarged prostate)
  • Neurogenic bladder (e.g., intermittent self-catheterisation in multiple sclerosis)
  • Surgery (during and after)
  • Output monitoring in acutely unwell patients (e.g., sepsis or intensive care)
  • Bladder irrigation (e.g., to wash out blood clots in the bladder)
  • Delivery of medications (e.g., chemotherapy to treat bladder cancer)


A bladder scanner can be used to measure the volume of urine in the bladder. A post-void bladder scan (measured after the patient attempts to empty their bladder) can indicate the need for a catheter (e.g., more than 500mls). 

TOM TIP: A common presentation requiring catheterisation is an older man presenting acutely with urinary retention due to an enlarged prostate. Typical management involves inserting a catheter, starting tamsulosin (an alpha-blocker) and discharging the patient to have a trial without a catheter (TWOC) in the community. It is worth remembering tamsulosin for your exams, as they may give you this scenario and ask what medication should be started. The key side effect to remember is postural hypotension, leading to dizziness on standing or falls. 


Types of Catheter

Urethral catheters are inserted through the urethra into the bladder. There are various types:

  • Intermittent catheters – simple catheters used to drain urine, then immediately removed
  • Foley catheter (two-way catheter) – the “standard” catheter with an inflatable balloon to hold it in place
  • Coudé tip catheter – has a curved tip to help navigate it past an obstruction during insertion
  • Three-way catheter – has three tubes used for inflating the balloon, injecting irrigation and drainage


Suprapubic catheters are inserted through the abdomen into the bladder, just above the pubic symphysis, under local anaesthetic. An inflated balloon holds them in place in the same way as a urethral catheter. When used long term, they can be easily replaced at regular intervals by an appropriately trained person.

TOM TIP: The catheter you will see most often on the wards and in OSCEs is the Foley catheter (two-way catheter). It might not be possible to insert a Foley catheter into a man with acute urinary incontinence due to an enlarged prostate. If using a Foley catheter fails, it is worth giving a Coudé tip catheter a try, as the slightly rigid curved tip can make bypassing an obstruction much easier. One of the most rewarding jobs as a junior doctor is inserting a catheter for someone in acute urinary retention, where you can almost immediately relieve a patient’s pain and distress.


Trial Without Catheter

A trial without a catheter (TWOC) involves removing a urethral catheter to see if a patient can manage without it. After the catheter is removed, the urine output is monitored, and a bladder scanner is used to make sure there is minimal residual urine left in the bladder. They may “fail” the TWOC, in which case another catheter is inserted.


Catheter-Associated Urinary Tract Infections

Infections are a key complication of urinary catheters. The longer the catheter is in place, the more likely bacteria are to grow in the urine. A sample of urine should be taken directly from the catheter or sample port using an aseptic technique (not from the catheter bag as this may be contaminated).

There are NICE guidelines on catheter-associated urinary tract infections from 2018, please see the full guidelines when treating patients.

Patients without symptoms do not generally require antibiotics for bacteria in the urine (bacteriuria) if they do not have symptoms.

Patients with symptoms require treatment with 7 days of antibiotics. Depending on the severity of symptoms, this may be with oral antibiotics or require admission to hospital and IV antibiotics. The catheter should be changed as soon as possible (but not delaying antibiotics).


Last updated May 2021
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