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Catheterisation #1: Essential Foundations

Catheters are common. 15-25% of hospital patients will be catheterised. Competence in catheterisation is assessed at medical school and is a requirement for successful completion of foundation training, yet, in spite of this, inserting catheters correctly and looking after patients with catheters can be challenging for junior doctors.

This series aims to take you though the important basics of catheter insertion, what steps the urologists take when you call them for help and finally to share some useful anecdotal advice learned the hard way from years on the wards.


The Essentials

This is the first in a series on catheterisation. It is followed by Part #2, Part #3, and Part #4. This series aims to take you though the important basics of catheter insertion, what steps the urologists take when you call them for help and finally to share some useful anecdotal advice learned the hard way from years on the wards.

1. Uses for Catheters

Catheters are most commonly used for draining – for managing continence, treating urinary retention, monitoring fluid output accurately or for drainage of stenosed stomas.

In the more specialist setting they are also used for instillation of therapeutic agents into the bladder – such as mitomycin or BCG in bladder cancer, or hyaluronic acid for painful bladder syndrome.

They can also be used for diagnostics in urodynamic studies and cystograms.

All catheters are a standard length – being between 40 and 45cm in length, allowing safe use in men. There are also female catheters available which are usually 25cm long, but these have disappeared from hospitals, and for good reason. Although 25cm is a good length for female catheterisation, if used in a male, even with the catheter inserted as far as it will go, inflating the balloon can lead to significant urethral injury. Female catheter packs have a red warning sticker and if you do see one at the back of a dusty store cupboard, don’t use them and let someone know.

2. Catheter Sizes

Catheter sizes are described in the French scale (Fr) which may also be abbreviated to Ch for Charrière, the Swiss-born French surgical instrument manufacturer who invented the scale. Fr and Ch can be used interchangeably, useful not least because French is easier to say than Charrière.

The French size equates to roughly three times the external diameter in mm – so a 16 Fr catheter has a diameter of 5.3mm, and a 20 Fr has a diameter of 6.6mm. Thankfully, the colour of the cuff on the catheter balloon port corresponds to the catheter size, White = 12Fr, Green = 14Fr, Orange = 16Fr, Red = 18Fr, Yellow =20Fr.

As the French size increases so does the external diameter of the catheter. This is the opposite of the Birmingham gauge, which was developed for use in wire manufacturing. In the Birmingham gauge, an increasing gauge means a smaller size. The Birmingham gauge is used for cannulas.

When deciding which catheter to use, a good rule of thumb is use the smallest tube required for purpose. Most urologists would use a 16Fr for male catheterisation, and a 14Fr for female..

3. Two- and Three-Way Catheters

Frederic Foley was an American Urologist born in Minnesota in 1891. He graduated from Johns Hopkins in 1918, and in 1929 described his invention: the self-retaining balloon catheter. This is essentially the same design used in catheters today, namely an indwelling urinary catheter with a balloon incorporated towards the tip – allowing it to remain in the bladder without the need for external strapping.

Two-way catheters have two channels – one for urinary drainage, and the second to inflate the balloon. Three-way catheters have an addition channel, used to deliver fluid in order to irrigate the bladder and wash out any blood before it can form clots. Three-way catheters tend to be larger, starting at 18Fr. The larger the three-way, the larger the drainage holes, and the bigger the blood clots that can be removed through them. For clot retention, a 22Fr three-way is a good size to start with.

4. Catheter Tips

There are as many different tips to catheters as the manufacturing companies can think up a purpose for. The most commonly encountered ones are described here.

The standard catheters are constructed with a rounded closed-ended tip. They have eyelets to either side of the tip for drainage, or, instillation.

In situations where an indwelling catheter is not required, such as Clean Intermittent Self-Catherisation (CISC), open tipped catheters are used. These are often referred to as In-Out catheters as they do not have a self-retaining balloon and after the bladder is drained, are removed and disposed of. There is a wide range of these catheters including collapsible, telescopic constructions enabling them to be carried discretely. There are no side drainage holes and the bladder is emptied through the open tip.

Curved tip catheters. These are often the urologist’s best friend and have certainly helped me out of some potentially difficult situations in the middle of the night. Again, there is a wide range of curved tip catheters which come in both 2- and 3-way constructions. When inserted the curve allows the tip to follow the anterior surface of the urethra and so are more inclined to successfully navigate the bend in the bulbar urethra and prostatic fossa in men, where a normal catheter may get stuck. Coudé and Tiemann tip catheters are commonly-found examples of curved tip catheters.

Remember! Curved tip catheters often won’t have a syringe with water for the balloon packed with them. Make sure you check before you start.

5. Catheter Materials

There are three main materials types used in catheter manufacture:

Latex coated catheters are cheap, highly flexible and resistant to damage. The downside is that they can become encrusted quickly. They are usually coated with PTFE, hydro-gel or silicon.

All silicon catheters are more expensive than latex coated ones, they are slightly more rigid, but also have a larger internal diameter and are more suitable for longer term use (longer than 1 month and up to 3 months). Silicon catheters are essential in patients with latex allergy.

PVC catheters. Irrigating 3 way catheters are made of PVC. They are for short-term use only and patients should not be sent home with them. They are uncomfortable and rigid, but great for washing out clots.

Remember! Uncoated latex catheters are rarely if ever used due to allergy risk and rapid encrustation.


This is the first in a series on catheterisation. Click here to read Part #2.

Words by Dr. Paul Sturch.

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