Designs - Indwelling Catheters

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Bard timeline

Catheters are fairly rigid structures. They drain the bladder but block the urethra.

catheter eyeThe catheter should have a smooth surface with two drainage eyes at the tip that allow for urine drainage.

Drainage eyes are placed either laterally or opposed. Opposing drainage eyes generally facilitate better drainage.

Catheter products have changed significantly in their composition, texture, and durability since the 1990s.

The challenge is to produce a catheter that matches as closely as possible to the normal physiological and mechanical characteristics of the voiding system.

This requires construction of a thin-walled, continuously lubricated, collapsible (conformable) catheter to protect the integrity of the urethra; a system to hold the catheter in place without a balloon; and a design to imitate the intermittent washing of the bladder with urine.

 Catheter Tips

The most commonly used catheter is a straight-tipped catheter.

coude tipA Coudé-tipped catheter, or Tiemann catheter, is angled upward at the tip to assist in negotiating the upward bend in the male urethra.  

This feature facilitates passage through the bladder neck in the presence of obstruction from a slightly enlarged prostate gland (e.g., in benign prostatic hyperplasia).

The Carson catheter is a slightly larger bulb to assist in negation of restrictions. 

The Council catheter features a reinforced hole at the tip of the catheter.

A whistle-tipped catheter is open at the end and allows drainage of large amounts of debris (e.g., blood clots).

Catheter Size and Length

Each catheter is sized by the outer circumference and according to a metric scale known as the French (Fr) gauge (range is 6 to 18 Fr), in which each French unit equals 0.33 mm in diameter.

The golden rule is to use the smallest catheter size (termed bore), generally 14 to 16 Fr, that allows for adequate drainage.

The use of large-size catheters (e.g., 18 Fr or larger) is not recommended because catheters with larger diameters can cause more erosion of the bladder neck and urethral mucosa, can cause stricture formation, and do not allow adequate drainage of periurethral gland secretions, causing a buildup of secretions that may lead to irritation and infection. Also, large catheters can cause pain and discomfort.  

Balloon SIze

A retention balloon prevents the catheter from being expelled. The preferred balloon size may be labeled either 5 mL or 10 mL, and both are instilled with 10 mL of sterile water for inflation per manufacturer’s instructions.

french sizesA fully inflated balloon allows the catheter tip to be located symmetrically. If a 5 mL balloon is inflated with more than 10 mL of water, irritation may occur unilaterally on the bladder wall from increased pressure of the balloon.

Underfilling or overfilling may interfere with the correct positioning of the catheter tip, which may lead to irritation and trauma of the bladder wall.

The catheterized bladder is in a collapsed state as a result of constant urine drainage. However, a 30 mL balloon will allow persistence of a small pool of undrained urine, so the bladder emptying is not complete.

A balloon with a fill size greater than 10 mL, such as a 30 mL balloon, is not recommended because the 10 mL size keeps residual urine minimal, thus reducing the risk of infections and irritation.

The use of a larger balloon size is mistakenly believed by many nurses to be a solution to catheter leakage or urine bypassing around the catheter. However, a large balloon increases the chance of contact between the balloon or catheter tip and the bladder wall, leading to bladder spasms that may cause urine to be forced out around the catheter.

The 30 mL balloons are used primarily to facilitate traction on the prostate gland to stop bleeding in men after prostate surgery or to stop bleeding in women after pelvic surgery.

Routine use of larger capacity balloons (30 mL) should be avoided for long-term use as they can lead to bladder neck and urethral erosion.

In men, the catheter should be passed initially to the bifurcation (the “Y” junction where the balloon arm and catheter meet) to ensure that the balloon will not be inflated in the urethra. 

Catheter Materials

A wide range of catheter materials are available, and the material selected should be chosen by: 

  1. how long the catheter will remain in place,
  2. comfort,
  3. the presence of latex sensitivity,
  4. ease of insertion and removal, and
  5. ability to reduce the likelihood of complications such as urethral and bladder tissue damage, colonization of the catheter system by microorganisms, and encrustation

lubrisilSilicone-coated latex catheters have a chemically bonded coating of silicone elastomer.

Teflon prevents urethral contact with the latex Teflon-coated catheters, which are thought to reduce the rate of absorption of water 100%.

Silicone catheters are thin-walled, rigid catheters with a larger diameter drainage lumen.

Hydrogel-coated latex catheters absorb water to produce a slippery outside surface.

Antimicrobial catheters are antibacterial with a silver alloy.

Note: Several catheter materials have been found to lose water from an inflated balloon; 100% silicone catheters can lose as much as 50% of volume within 3 weeks. Prior to insertion, all indwelling catheters should be visually inspected for any imperfections or surface deterioration.

Latex Catheter - Problems 

It is important for the clinician to be aware of the results of research on the use of certain types of indwelling catheters.

There are reported increases in allergies and reactions in patients with long-term use of all urinary latex and rubber catheters. Patients who have asthma and other allergies are at increased risk for these allergies. Latex allergy can result in symptoms such as skin irritation, rashes, and blisters. Urethritis and urethral strictures can also result from latex allergies.

latex foleyCoatings such as silicone and polytetrafluoroethylene (PTFE) are used to coat latex catheters.

Hydrogel coating, which remains intact when used, has demonstrated the ability to reduce the high level of cytotoxicity associated with latex catheters. However, coated latex catheters do not protect against an allergic reaction to the underlying latex because the coating wears off.

Silicone- and hydrogel-coated catheters usually last longer than PTFE-coated catheters. If the person is latex sensitive, silicone catheters should be used. Avoiding latex catheters may also decrease the incidence of encrustation. All-silicone (100%) catheters are biocompatible and are believed to have encrustation-resistant properties.

Bonded hydrogel-coated latex catheters may be longer lasting than silicone catheters because their hydrogel coating prevents bacterial adherence and reduces mucosal friction. Hydrogels or polymers coat the catheter, absorbing water to produce a slippery outside surface. This results in the formation of a thin film of water on the contacting surface, thus improving its smoothness and lubricity. These properties might act as potential barriers to bacterial infection and reduce the adhesion of both gram-positive and gram-negative bacteria to catheters. 

A major problem with Foley catheters is that they have a tendency to contribute to urinary tract infections (UTI). This occurs because bacteria can travel up the catheters to the bladder where the urine can become infected. To combat this, the industry is moving to antiseptic coated catheters. This has been helpful, but it has not completely solved this major problem. An additional problem is that Foley catheters tend to become coated over time with a biofilm that can obstruct the drainage. This increases the amount of stagnant urine left in the bladder, which further contributes to the problem of urinary tract infections. When a Foley catheter becomes clogged, it must be flushed or replaced.

Preventing Bacterial Colonization

In an attempt to prevent bacterial colonization, catheters have been coated with silver alloy or nitrofurazone, a nitrofurantoin-like drug.

A systematic review of these catheters determined that bacteriuria can be decreased by their use in hospitalized patients.
Both nitrofurazonecoated and silver alloy-coated catheters seem to reduce the development of asymptomatic bacteriuria during short-term (< 30 days) use.
Despite their unit cost, there is a suggestion that these devices might be a cost-effective option if overall numbers of infections are significantly reduced through their use.

Antibiotic-Coated Catheters

Antibiotic-coated catheters were found in a meta analysis to prevent or delay bacteriuria in short-term catheterized, hospitalized patients.

Silver Alloy-Coated Catheters

Silver alloy-coated catheters are thought to cause less inflammation and have a bacteriostatic effect because they reduce microbacterial adherence and migration of bacteria to the bladder.
Because they prevent bacterial adherence, these catheters also minimize biofilm formation through their release of silver ions that prevent bacteria from settling on the surface.  
There appear to be few adverse effects, and microbial resistance to the active agent is unlikely. 


  1. Ahearn, D. G., D. T. Grace, et al. (2000). "Effects of hydrogel/silver coatings on in vitro adhesion to catheters of bacteria associated with urinary tract infections." Current Microbiology 41: 120-125.
  2. Brosnahan, J., A. Jull, et al. (2004). "Types of urethral catheters for management of short-term voiding problems in hospitalized patients." Cochrane Database of Systematic Reviews (1): CD004013.
  3. Gray, M. (2006). "Does the construction material affect outcomes in long-term catheterization?" JOCN 33: 116-121.
  4. Lawrence, E. L. and I. G. Turner. (2005). "Materials for urinary catheters: A review of their history and development in the UK." Med Engineering Phys 27: 443-453.
  5. Moy, L. M. and A. J. Wein. (2007). Campbell’s Urology, 9th ed. Elsevier-Saunders; Philadelphia, PA: 2288-2304.
  6. Newman, D. (2007). "The indwelling urinary catheter: Principles for best practice." JOCN 24: 655-661.






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