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Bladder Catheter: Material, Catheter Sizes, and Catheter Tips

Bladder catheters are used to drain the bladder and are integral to urological practice, serving various diagnostic, therapeutic, and perioperative functions.

Classification of Bladder Catheters

• Transurethral bladder catheter
  • Indwelling catheter (Foley catheter)
  • Intermittent catheter
  • Bladder irrigation catheter (Three-way catheter)
  • Measurement catheter for urodynamics
• Suprapubic Indwelling Catheter

Materials of Bladder Catheters

Transurethral catheters are manufactured from PVC, latex, polyurethane, or silicone.

Polyvinyl Chloride (PVC):

PVC is a rigid and brittle plastic that becomes flexible and soft through the addition of plasticizers. PVC catheters are cost-effective and are used for intermittent catheterization or as measurement catheters in urodynamics. The biocompatibility of PVC is not ideal, making PVC catheters unsuitable for long-term indwelling bladder catheterization.

Latex:

Latex is a polymer (polyisoprene) derived from natural rubber. Since the invention of vulcanization by Charles Goodyear in 1839, latex catheters have been available in medicine. Latex catheters are very soft, offer high comfort, and are inexpensive. Disadvantages include rapid encrustation, which carries the risk of blockage, and the possibility of latex allergy.

Polyurethane:

Polyurethane is a polymer with linked urethane groups. Polyurethane allows for cost-effective, latex-free catheter production. Its biocompatibility is lower than that of silicone.

Silicone:

Silicones are a group of synthetic polymers in which silicon atoms are connected via oxygen atoms and simultaneously carry hydrocarbon groups (chemically poly(organo)siloxanes). Silicone has the highest biocompatibility and is therefore best suited for long-term catheterization.

Bladder Catheter Tip Shapes

Common straight and angled catheter tip shapes:

• Nelaton (or Robinson): Straight catheter with a rounded tip. Most common normal form.
• Olive Tip: Olive-shaped, tapered, straight catheter tip. Helpful to navigate through narrow urethras.
• Couvelaire: Straight catheter end with a flute-shaped tip and a large opening, used for hematuria catheters.
• Mercier: Catheter tip similar to Nelaton with a 30-degree angled catheter end. Helpful to navigate past an enlarged prostate.
• Tiemann: Olive-shaped, tapered straight catheter tip with a 30-degree angled catheter end. Helpful to navigate past an enlarged prostate.
• Dufour: 30-degree angled catheter end with a flute-shaped tip and a large opening, used for hematuria catheters, helpful to navigate past an enlarged prostate or after TURP.

Catheter Sizes in French or Charrière

Charrière is the historic unit for the outer diameter of medical instruments or catheters (abbreviations: Ch, Charr., or CH; English synonym: French). It is still used in continental Europe. Since Charrière is hard to pronounce and spell, the name of the unit was simplified to "French (Fr)". One French or one Charrière equals an outer diameter of 0.33 mm. To convert to millimeters, divide French or Charrière by 3; thus, an 18 Fr catheter has a diameter of 6 mm. The circumference in millimeters approximately corresponds to the Charrière units.

Parameters Affecting Catheter Drainage Capacity:

The ability of a catheter to drain fluid mainly depends on the radius of its inner lumen. According to Hagen–Poiseuille’s law (which applies to Newtonian fluids), laminar flow increases with the fourth power of the lumen radius. In simple terms, even a slight increase in the internal diameter makes a huge difference: doubling the inner diameter increases flow capacity by a factor of sixteen. In everyday urology, this principle is clearly noticeable, but things become more complex when hematuria is present. Clot formation can block drainage openings and reduce the expected flow (leading to bladder tamponade), making it harder to compare catheter performance in practice.

It is also important to realize that not all catheters with the same outer diameter have the same inner diameter. Differences in wall thickness, material, design, and manufacturer can significantly change the effective drainage capacity. Other relevant factors include the number and size of the side holes, the stiffness of the catheter wall (important if clots need to be aspirated manually), and the length of the catheter (the differences are usually negligible).

References

Gambrill B, Pertusati F, Hughes SF, Shergill I, Prokopovich P. Materials-based incidence of urinary catheter associated urinary tract infections and the causative micro-organisms: systematic review and meta-analysis. BMC Urol. 2024 Aug 30;24(1):186. doi: 10.1186/s12894-024-01565-x.

Robinson J. Urethral catheter selection. Nurs Stand. 2001 Mar 7-13;15(25):39-42. doi: 10.7748/ns2001.03.15.25.39.c2993.

Sökeland, J., Brühl, P., Hertle, L., and Piechota, H. (2000). Katheterdrainage der Harnblase heute.
Dtsch Arztebl, 97(4):A167-A174.

  Deutsche Version: Material und Einteilung der Harnblasenkatheter

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