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Abstract

Eighty per cent of Urinary Tract Infections (UTIs) are associated with the presence of a urinary catheter. Alarmingly Patients with a UTI are also three times more likely to die with a fatality rate from urinary tract related bacteraemia is around 13%. (1-6). Infection is due to encrustation of the urinary catheter (7) It has been suggested that urinary catheters which have smoother drainage apertures are less prone to struvite formation and subsequent  catheter encrustation (8). It is, therefore, advisable that catheters are manufactured with perfectly smooth surfaces and apertures to reduce the potential for infection. An ultrasonic cutting technology is described here that produces smooth apertures and eliminates problems associated with debris.

The clinical problem

A urinary catheter is designed to drain the bladder of urine or allow the instillation of fluids into the bladder.   To allow this functionality, a urinary catheter is a hollow polymeric tube which a perforated tip or ending.  More than 12% of patients in hospital are catheterised (1-3) and studies have  shown that urinary tract infections account for 23% of all hospital-acquired infections.  44% of hospitalised patients with indwelling catheters have been found to develop significant bacteriuria within 72 hours of catheterisation.(1)  Thus, almost all patients will have an infection after approximately four weeks, which can extend a hospital stay by an extra three days. Patients with a UTI are also three times more likely to die; the fatality rate from urinary tract related bacteraemia is around 13%.(5)

The problem stems from an infection by urease producing bacteria such as Proteus Mirabilis.  These bacteria tend to adhere and colonise catheter surfaces producing a biofilm or coating.  This biofilm secretes urease which releases ammonia and increases the microenvironmental pH around the luminal surface of the catheter (7).  An elevated pH induces the precipitation of magnesium and calcium phosphate crystals from urine to form struvite which is an abrasive material capable of damaging urinary tract tissue and also blocking the urinary catheter leading to infection.  In clinical practice this process manifests itself and is often described as encrustation.

Importance of high quality manufactured catheters

A particular cause for concern is the texture and shape of the apertures that are formed within the catheter wall.  These apertures are required to allow drainage of urinary fluids and therefore they must be perfectly smooth and free from burrs.  Most apertures are created by mechanical cutting or piercing/puncturing of the catheter body.  These methods have limitations in that they cannot always reliably produce smooth apertures or guarantee the removal of any debris from the punctured or perforated catheter body (9).

Studies by the School of Biosciences at Cardiff University (10) using their artificial bladder model found that the process of encrustation is started by initial cell adhesion of Proteus Mirabilis to irregular surfaces surrounding the catheter eye or drainage holes.  Micro-colonies form in the depressions of the cut surfaces allowing the formation of the biofilm from which the urease enzymes are released causing the precipitation of the struvite material.  Although different polymeric materials have lower affinities for cell adhesions i.e. silicone material has a lower susceptibility to encrustation compared to latex catheters.The major initiation factor was deemed to be the quality of the of the aperture edge and surfaces.  These workers (10) found using scanning electron microsopy that  engineering techniques used in catheter manufacturing processes produce particularly rough irregular surfaces on the rims (edges) of the drainage holes (eyes), quoting:

‘Catheters available today with their rough, engineered, irregular surfaces around the eye holes and narrow central channels are readily colonized and blocked by crystalline bacterial biofilm.  The development of cathters with larger internal diameters and smoother surfaces especially around the eye holes would substantially reduce the problems with current devices’.

An ultrasonic processing solution

Using ultrasonic processing technology, specialised tooling has been developed that can be used to cut and form an aperture through a catheter body, which has advanced the production of smooth apertures.  

The tooling or sonotrodes are constructed from solid titanium are connected to thruster-booster coupling which is designed to vibrate the tip longitudinally from 15,000 to 40,000 Hz (11).

The high vibrational forces which are developed allow the titanium sonotrodes to precisely and efficiently cut through polymeric surfaces.  This cutting action combined with an unique profile design allows the creation of aperture with smoother edges and surfaces.

In addition, this technology has solved another problem inherent in the general manufacturing process, that is, the removal of the chad or debris that is generated when the aperture is cut .

In conventional manufacturing processes the chad can be left partially attached to the edge if the cut is not made cleanly or it can be pressed through into the hole and lost within the catheter bore.  In both scenarios, unless the error is detected immediately, currently by visual inspection, the chad can still be in situ when the catheter is inserted into the patient’s urinary tract, which would cause trauma to the surrounding tissues and/or dislodge to cause blockages or other serious complications.

The ultrasonic technique combines a vacuum drawing system within the ultrasonic cutting tool so that when an aperture is cut, the vacuum simultaneously removes the chad and conveys it to an electronic counter. If a chad is not counted for each aperture that is cut, then the manufacturing process is automatically stopped and can only be restarted when the faulty catheter is physically removed and disposed off, which ensures 100% elimination of a problem with missing chads.

Conclusion

In summary, UTIs are associated with the use of urinary catheters and which is in turn related to the way these catheters are manufactured.  It is evident that the quality of the apertures with respect to surface finish plays a key role in the initiation of bacterial adherence, biofilm formation and the precipitation of struvite and ultimate encrustation of the catheter.  The need for better quality apertures and manufacturing process will help reduce the number of UTIs seen in clinical practice.

It is worth quoting the words from Stickler and co-workers, (10) as follows:

‘There is a need to improve catheter design and manufacturing procedures for the eye holes if the problems associated with the current devices are to be reduced’

References

1. R. Crow et al., “Study of Patients with Indwelling Urethral Catheters and Related Nursing Practice,” Nursing Practice Research Unit, University of Surrey, Guildford, UK (1986).

2. B. Roe, “Catheters in the Community,” Nursing Times, 84, 36, 43–44 (1989).

3. A.M. Emmerson et al., “The Second National Prevalence Survey of Infection In Hospitals — Overview of the Results,” Journal of Hospital Infection, 32, 175–190 (1996).

4. Report from the Medical Officer of Health, “Winning Ways — Working Together To Reduce Healthcare Associated Infection in England,” Department of Health (December 2003).

5. S. Saint and B.A. Lipsky, “Preventing Catheter-Related Bacteriuria.  Should We? Can We? How?” Archives of Internal Medicine, 159, 800–808 (1999).

6. K. Getliffe , “Freeing the System,” Nursing Standard, 3, 8, 16–18 (1993).

7. D Stickler, N Morris, M-C Moreno and N Sabbuba, Studies on the formation of crystalline bacterial biofilms on urethral catheters, Eur. J. Clin. Microbiol. Infect. Dis. 17: 649-652. (1998).

8. N S Morris, D J Stickler and C Winters, Which indwelling urethral catheters resist encrustation by Proteus Mirabilis biofilms, British Journal of Urology, 80:58-61. (1997).

9. L Martini and A L Profit, Manufacturing high quality catheters,European Medical Device Technology, Janury 2009 available at www.emdt.co.uk, accessed 23rd January 2011.

10. D. Stickler, R young, G Jones, N Sabbuba and N Morris, why are Foley catheters so vulnerable to encrustation and blockage by crystalline bacterial biofilm?  Urol Res, 31:306-311 (2003).

11.A L Profit and L Martini Using Ultrasonic Technology to manufacture products, Medical Device Technology, 17:30-31 (2008).

A.L. Profit is Owner and Co-Director at Rainbow Medical Engineering Ltd

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