Understanding Urinary Catheter Basics

Urinary Catheter sizes are based on a system called the French Gauge (abbreviated fr) that was developed in the 19th century by a French manufacturer of medical instruments, Joseph Frederic Benoit. The size, pronounced “French”, refers to the outside diameter of the tube, the bigger the number the bigger the catheter. One French in size is roughly 1/3 of a millimeter.

For easier identification each French size has a corresponding color code. Color coding for commonly used adult size catheters are as follows:

  • White for sizes 5 and 12
  • Green for sizes 6 and 14
  • Blue for sizes 8 and 24
  • Black for size 10
  • Orange for size 16
  • Red for size 18
  • Yellow for size 20
  • Brown for size 22

Please see the image above.

Discuss with your physician the right catheter size for you

Using the right size is important because too big a catheter can cause injury. If insertion is through the urethra (as opposed to a supra-pubic incision), an injury can lead to significant bleeding and urethral strictures. Too small a catheter on the other hand can generate leakages and soiling which can bring complications especially in bedridden patients.

The average length of the urethra determines the length of the catheter.

Catheters are grouped into three categories according to their lengths:

  • Pediatric catheters measure between 8-10 inches long.
  • Female adult catheters measure 6-8 inches long.
  • Male adult catheters are the longest at 16 inches and up.

Catheters are further classified according to their type and intended use:

Intermittent Straight Catheters

Intermittent Straight Catheters

These catheters are made of flexible usually clear tubing with a smooth tip and a hole on one side. They relieve patients with a full bladder when unable to empty due to obstruction or due to spinal injuries. This catheter is a short term catheter (it’s not left in place for days at a time) so urine draining must be done several times a day. The risk of urinary tract infections is high with intermittent catheterization unless high aseptic techniques are observed.

Intermittent Coude Catheters

Intermittent Coude Catheters

The purpose and use of this type of catheter is the same as the intermittent straight catheter. It is only in design that they differ. The tip of this catheter is curved for about an eighth of an inch to facilitate catheterization in patients with enlarged prostates. A straight catheter would usually hit a dead end with no way to manipulate it through. Well-designed catheters in this group have a raised edge on the holding side that corresponds with the curve that goes into the urethra. This makes it easier to know where the curve is facing once the catheter is in the urethra. The catheter can also be used in women suffering from urethral strictures and obstructions. Hygiene is paramount here just as in intermittent straight catheterization.

Intermittent Closed System Catheters

Intermittent Closed System Catheters

These catheters enable a ‘touch-free’ technique. The catheter remains in its packaging while the catheterization is done through an introducer. There is no contact with the hands or the outside. The urine then collects in a bag. This type of catheter greatly reduces the risk of UTI.

Closed system catheters create great convenience for sportsmen, frequent travelers and other active, though disabled, persons. The freedom this method offers help these patients gain confidence and play a more active role in their communities.

Foley Catheters

Foley Catheters

Sometimes a catheter must remain inside the bladder long periods of time as opposed to being inserted and dislodged various times during the day. Such long term catheters are called indwelling or Foley catheters. A Foley catheter anchors to the bladder floor through a balloon located at the catheter’s distal end. Once the catheter enters the bladder the balloon is filled with sterile water securing it in place. Just like an intermittent catheter a Foley catheter can be inserted through the urethral canal or through a suprapubic incision on the lower abdomen. Once the Foley catheter reaches the bladder, the balloon is filled with sterile water. The weight of the water prevents the catheter from exiting the bladder. Foley catheters must be changed every 2-4 weeks.

Hydrophilic Catheters

Hydrophilic Catheters

These catheters are ideal for people prone to painful catheter insertions. The catheters are pre-lubricated with a water soluble lubricant for easy and pain-free transition along the urethra. The hydrophilic layer remains lubricated for the duration of the catheterization ensuring continued patient comfort.

External Catheters

External Catheters

These are used mostly by males with urinary incontinence. Female types exist but are not common owing to their difficult application. Males slide the sheath over their penis and hold it with an adhesive or foam strap around the penis. The urine collects in a tube that is connected to a urine bag. The sheath can be made from latex rubber, silicon or vinyl.

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