The Royal Marsden Hospital Manual of Clinical Nursing Procedures - Lisa Dougherty [178]
Tip design
Several different types of catheter tip are available in addition to the standard round tip (Figure 6.5). Each tip is designed to overcome a particular problem.
Figure 6.5 Catheter tips.
The Tiemann-tipped catheter has a curved tip with one to three drainage eyes to allow greater drainage. This catheter has been designed to negotiate the membranous and prostatic urethra in patients with prostatic hypertrophy.
The whistle-tipped catheter has a lateral eye in the tip and eyes above the balloon to provide a large drainage area. This design is intended to facilitate drainage of debris, for example blood clots.
The Roberts catheter has an eye above and below the balloon to facilitate the drainage of residual urine.
Catheter material
A wide variety of materials are used to make catheters. The key criterion in selecting the appropriate material is the length of time the catheter is expected to remain in place. Three broad timescales have been identified.
Short term (1–7 days, e.g. PVC and intermittent catheters).
Short to medium term up to 28 days: for example PTFE.
Medium to long term (6 weeks–12 weeks): e.g. hydrogel and silicone coated.
The principal catheter materials are as follows.
Polyvinyl chloride (PVC)
Catheters made from PVC or plastic are quite rigid. They have a wide lumen, which allows a rapid flow rate, but their rigidity may cause some patients discomfort. They are mainly used for intermittent catheterization or postoperatively. They are recommended for short-term use only (Pomfret 1996).
Latex
Latex is a purified form of rubber and is the softest of the catheter materials. It has a smooth surface, with a tendency to allow crust formation. Latex absorbs water and consequently the catheter may swell, reducing the diameter of the internal lumen and increasing its external diameter (Pomfret 2003, Robinson 2001). It has been shown to cause urethral irritation (Wilksch et al. 1983) and therefore should only be considered when catheterization is likely to be short term.
Hypersensitivity to latex has been increasing in recent years (Woodward 1997) and latex catheters have been the cause of some cases of anaphylaxis (Young et al. 1994). Woodward (1997) suggests that patients should be asked whether they have ever had an adverse reaction to rubber products before catheters containing latex are utilized.
Teflon (polytetrafluoroethylene [PTFE]) or silicone elastomer coatings
A Teflon or silicone elastomer coating is applied to a latex catheter to render the latex inert and reduce urethral irritation (Slade and Gillespie 1985). Teflon is recommended for short-term use and silicone elastomer-coated catheters are used for long-term catheterization.
All silicone
Silicone is an inert material which is less likely to cause urethral irritation. Silicone catheters are not coated and therefore have a wider lumen. The lumen of these catheters, in cross-section, is crescent or D-shaped, which may induce formation of encrustation (Pomfret 1996). Because silicone permits gas diffusion, balloons may deflate and allow the catheter to fall out prematurely (Barnes and Malone-Lee 1986, Studer et al. 1983). These catheters may be more uncomfortable as they are more rigid than the latex-cored types (Pomfret 2003). All-silicone catheters are suitable for patients with latex allergies. Silicone catheters are recommended for long-term use.
Hydrogel coatings
Catheters made of an inner core of latex encapsulated in a hydrophilic polymer coating are commonly used for long-term catheterization. The polymer coating is well tolerated by the urethral mucosa, causing little irritation. Hydrogel-coated catheters become smoother when rehydrated, reducing friction with the urethra. They are also inert (Nacey and Delahunt 1991), and are reported to be resistant to bacterial colonization and