| Abstract|| |
Continuous ambulatory peritoneal dialysis has become a practical and safe mode of therapy for patients with end-stage renal disease. The creation of a durable, safe and efficient peritoneal access has been made possible through refinements in catheter design. The Tenckhoff catheter and its modifications has remained the most popular peritoneal access devise over the last 25 years. The major objectives' in catheter design include ensuring biocompatibility, ease with which the catheter can be implanted and removed as well as esthetic appeal. The other features in a peritoneal dialysis catheter are those that reduce catheter related complications such as catheter migration, exit-site and tunnel infections, flow restriction and catheter cuff erosion. Although the perfect peritoneal catheter remains elusive as yet, refinements in design and manufacturing materials have facilitated the implantation and maintenance of the catheter resulting in better dialysis technique survival, lesser morbidity and greater patient acceptance.
Keywords: CAPD, Peritoneal dialysis catheter, Tenckhoff catheter.
|How to cite this article:|
El-Shahat YI, Cruz C. The Impact of Catheter Design on Preventing CAPD Complications. Saudi J Kidney Dis Transpl 1995;6:275-9
|How to cite this URL:|
El-Shahat YI, Cruz C. The Impact of Catheter Design on Preventing CAPD Complications. Saudi J Kidney Dis Transpl [serial online] 1995 [cited 2013 May 19];6:275-9. Available from: http://www.sjkdt.org/text.asp?1995/6/3/275/40661
| Introduction|| |
Recent refinements in the design and manufacture of peritoneal dialysis systems and methods of connection-disconnection, coupled with a better understanding of issues concerning dialysis adequacy, have contributed to make continuous ambulatory peritoneal dialysis (CAPD) a practical, safe and cost-effective therapy for patients with end-stage renal disease. Similarly, the creation of a durable and efficient peritoneal access, (mandatory for effective treatment) has been made possible through refinements in catheter design and a better understanding of the importance of catheter-host interaction as well as the function of the catheter-dialysis system as a unit.
| Historical Perspective|| |
The efforts to establish a functional and durable conduit between the intra-peritoneal space and the exterior in order to use the peritoneum as a dialysis membrane began in the early 1920's and went largely unrewarded for almost four decades.
Early peritoneal dialysis catheters, made mainly of surgical rubber, stainless steel, glass or PVC, were fraught with problems such as irregular flow, outflow obstruction, subcutaneous leaks and bacterial contamination resulting in a high failure rate. Consequently, peritoneal dialysis was not widely used and little progress was made in the areas of dialysis solutions, dialysis systems, cyclers and connections. Silicone rubber was first proposed as catheter material by Gutch in the early 1960's. It was the material used in the manufacture of the catheter designed by Palmer and Quinton in 1963. This device had improved hydraulic function.
The Tenckhoff catheter, first introduced in 1968, added two Dacron velour cuffs in the mid-section to the tubular structure of silicone rubber [Figure - 1]. These cuffs, by eliciting an inflammatory reaction in the surrounding tissue, result in the formation of a fibrous plug. Thus, the device gets structural support as well as a barrier that prevents bacterial contamination of the subcutaneous space caused by skin flora or from the peritoneum during episodes of peritonitis. The Tenckhoff catheter, in concert with closed dialysis systems and meticulous aseptic techniques for connecting and disconnecting, made peritoneal dialysis feasible for the first time.
The Tenckhoff catheter and/or modifications of this catheter have remained the most popular type of device over the last 25 years  . Modifications to improve its hydraulic function as well as reduce internal organ injury include making the distal segment coiled and bevelling the distal catheter tip. Also, catheters with two cuffs are preferred over those with one cuff. However, some practitioners, faced by a high incidence of cuff erosion which cannot entirely be attributed to a flaw in the catheter design or the cuff itself, have opted for using single-cuff catheters  .
In addition, an increasing awareness of the importance of the creation and orientation of the tunnel and exit-site has contributed to the popularity of catheters that have a shape and configuration which dictates the caudal orientation of the tunnel and exit-site  . The different types of peritoneal dialysis catheters in use now are shown in [Figure - 2].
| Major Objectives in Catheter Design|| |
A peritoneal dialysis catheter must allow the normal function of the surrounding tissue and should not elicit any local or systemic inflammatory or immune reaction. Biocompatibility is largely a function of the materials employed in catheter manufacture. For many years, silicone has been the material of choice for catheters designed for long-term use. Although fairly biocompatible, silicone has been implicated in the development of eosinophilic peritonitis and catheter entrapment by omental tissue. Also, inclusions of silica have been found in patients with sclerosing peritonitis  .
Newer materials like Tecoflex and Tecothane medical grade polyurethanes have been found to offer some advantages over silicone. Their thermoplasticity eliminates the stress on the subcutaneous tunnel and internal organs. Their smoother wall surface is less likely to harbor bacteria and biofilm. Also, silicone catheters have been reported to cause bowel perforation and injury to other internal organs when left in-situ following renal transplantation. Polyurethane catheters, which become very soft at body temperature, have not been reported to cause such problems  .
Ease of Implantation and Removal
Catheters of simple design (Tenckhoff, Cruz, Swan-Neck) can be easily implanted not only during an open surgical procedure but also by a simple "blind" approach or a laparoscopic method. Likewise, these catheters can be easily removed in the case of unresolved infection, a change in choice of treatment modality, or following successful renal transplantation ,, . The Cruz catheter is shown in [Figure - 3]. In contrast, catheters of complex design (TorontoWestern, Life Cath, and Valli) require the incision of the parietal peritoneum for their implantation and theoretically can be linked to a higher incidence of early dialysate leakage. Furthermore, the voluminous devices can serve as a nidus for infection leading to persistent peritonitis , . The different types of the Toronto-Western Hospital catheters available for use are shown in [Figure - 4],[Figure - 5].
For too long, the prospects of visible, cumbersome devices that interfered with patient comfort and/or ability to wear standard garments deferred many patients from undergoing peritoneal dialysis. Preshaped catheters (Cruz, Swan-Neck) dictate the placement of their exit orifice in the lower part of the abdomen and thus can be easily concealed and free from any interference by garments and garment belts.This feature and the wide availability of disconnect systems has been enthusiastically received by patients young and old , .
| Approaches to Reduce Catheter Related Complications|| |
This complication, often necessitating catheter replacement, is usually the result of a catheter that, having been implanted in a configuration other than its natural one, displaces itself away from the original placement site causing flow problems. Permanently bent catheters which do not place undue stress on the subcutaneous tissue nor try to" regain memory and straighten themselves, can prevent this complication. An additional feature is the placement of the radio-opaque line, precisely and uniformly in the 12 o'clock position of the catheter which facilitates implantation and guarantees the caudal unstressed position of the intra-abdominal segment of the catheter  .
Exit-site and Tunnel Infection
A combination of device features and implantation techniques address the problem of exit-site/tunnel infection. The tunnelling and retrieval tool included with every Cruz catheter, not only facilitates the tunnelling maneuver without causing tissue trauma, but also allows the implantation of catheters with built-in adaptors for the connecting system. The creation of a tunnel and exitsite in a caudal position (Cruz and Swan-Neck catheters) eliminates the accumulation of debris, sweat and water, thus eliminating the potential for infection , .
A catheter that exits caudally places less stress on the exit-site caused by the effect of gravity, than catheters that exit upward. Again, the thermoplasticity of polyurethane catheters contributes to a more stable and structurally sound tunnel and exit-site, reducing further the likelihood of infection ,, .
| Flow Restriction|| |
The dialysate flow characteristics of conventional silicone catheters are restrictive due to their small inner diameter (0.108 inch). This problem is compounded by the use of conventional adaptors for the connecting system which have an even smaller lumen and result in even further flow restriction. Catheters having larger inner diameter (0.130 inch) due to thinner walls, offer less flow restriction and provide measurable savings of inflow and outflow times. This feature combined with the presence of a built-in adaptor make possible significant increments in dialysate flow rates  . In the case of cycler assisted dialysis, it increases the dialysis efficiency by reducing the inflow-outflow time of each cycle.
| Catheter Cuff Erosion|| |
In addition to creating the exit-site at least 2.5 cm distal to the proximal cuff, the "pailhandle" feature of the Cruz catheters is designed to prevent cuff erosion by relieving the stress of tugging on the catheter. The "pail-handle" design has a straight subcutaneous segment which unlike the arcuate segment of Swan-Neck catheters, will not shift as a result of repeated traction on their external segment during the exchanges or by the effects of gravity , .
| Future Catheter Designs and Features|| |
Alternatives to the tubular (straight or coiled) intra-abdominal segment of catheters are being developed and show promise (TFluted Catheter, Ash, 1994) in terms of hydraulic function and freedom from omental interference. Newer polymers that can resist high temperature and the noxious action of solvents are being sought. The mating of catheters with silver and other metals to render them resistant to bacterial colonization has produced encouraging results in short-term studies. The greatest challenge however, continues to be the creation of a stable skin-catheter interface such as is seen in the case of antlers, teeth and hoofs, all of which protrude through the skin or other tegument without disruption. This will eliminate tunnel and exit-site infections.
| Conclusion|| |
The peritoneal dialysis catheter is the CAPD patient's life line. The perfect peritoneal catheter remains elusive as yet though the developments that have occurred in the last decade have improved the performance of the catheters and reduced the incidence of mechanical and infectious complications. These refinements in design and manufacturing materials that facilitate their implantation and maintenance have resulted in better dialysis technique survival, lesser morbidity and greater patient acceptance.
| References|| |
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Yassin I El-Shahat
Department of Nephrology, Al Jazeirah and Central Hospitals, Abu Dhabi
United Arab Emirates
[Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4], [Figure - 5]