Catheterisation is a simple procedure usually performed by either a doctor or a nurse. It involves passing a catheter usually a foley catheter into the bladder through either the urethra (urethral catheterisation) or through a small incision in the abdomen (supra-pubic catheterisation).

There are two main reasons for a catheter to be introduced. The first is if the patient is unable to urinate normally because they are bed-bound or unconscious, the second is if they are suffering from acute urinary retention.

If the patient is conscious at the time of urethral catheterisation, a lubricating jelly containing a local anaesthetic such as lignocaine would be used to ease the discomfort.

It is unusual, except in an emergency, for a supra-pubic catheterisation to be performed on an awake patient, however, in the case of acute urinary retention the discomfort caused by the placement of the catheter is often outweighed by the relief from the pain of urine retention.

Sometimes it is not possible for a person to urinate normally, and they must pass a catheter, usually a Nelaton catheter into the bladder themselves. Again there are two possible routes for this catheter to take. The first is the urethra and the second is via a appendicovesicostomy.

However the catheterisation occurs, the most important thing is that the procedure should remain as aseptic as possible. Catheterisation greatly increases the risk of urinary infection, which in turn increases the risk of calculi formation, and damage to the kidneys. It is generally accepted that the risk of infection is greater with indwelling catheters than with intermittant catheterisation although this may seem counter-intuitive. The risk can be minimised by regularly replacing the catheter, every 2 weeks is optimal althugh a catheter can be left in for upto 4 weeks and using a drainage bag (if fitted) with a non-return valve.

Catheters are one of the leading causes of nosocomial infection and care should always be taken when catheterising or maintaining a catheter.

Catheters are sized, that is the size of the bore, using the Charriere (Ch) or French (Fr) system where one unit is equal to one third of a millimetre. Catheters range in size from 6Ch/6Fr (2mm) to 26Ch/26Fr (8.7mm). The most commonly used catheters are 10Ch/10Fr (3.3mm), 12Ch/12Fr (4mm) and 14Ch/14Fr (4.7mm).