The Evolution of PD Catheters

Peritoneal access is an essential component of the PD system.  The evolution of PD catheter designs parallels the goals for an optimal peritoneal access and the availability of appropriate materials. 

The goals of peritoneal access are:

• Optimal and consistent hydraulic function
• Stable interface between catheter and body
• Minimal interference with abdominal function and clothing
• Maintenance free
• Infection free

The modern peritoneal access is the result of innumerable modifications to a simple tubular structure.  The process has been slow due to the many physical and biologic/ immunologic factors affecting its success.  Many trials with conduits to allow easy and repeated access to the peritoneum and with   catheters constructed with various materials and configurations were made.  The balance shifted with the introduction of the Tenckhoff catheter in 1968.

In 1968, Tenckhoff and Schecter revolutionized the field of peritoneal dialysis and introduced a permanent catheter and a method of implantation that for the first time allowed relatively long periods of usage with a significant reduction of infections¹.  They modified the Palmer catheter by eliminating the curled end (which they later reintroduced), shortening the length of the subcutaneous tunnel and attaching two Dacron felt cuffs.  Their four-part trochar allowed insertion of the catheter at the bedside with the use of local anesthesia.  Tenckhoff also proposed the use of a semiarcuate tunnel with a downward exit to reduce accumulation of debris and to minimize infection.

Making of Tenckhoff Cath

Click image to enlarge

Effective dialysate flow has been a principal concern in the design of all PD catheters.  Flow (Q) is determined by the pressure gradient across the end-points of the fluid pathway (P) and the hydraulic resistance of the system (R).

         Q = P/R

During inflow, the pressure gradient (P) is established by the distance between the top of the column of dialysate and the distal catheter tip.  Conversely, during outflow the pressure gradient depends on the distance between the intraperitoneal space and the drain bag.  As the distance between these points increases, gravity enhances flow velocity.  The hydraulic resistance (R) to flow depends largely on the size of the fluid channel.  Thus, the design and specifications of the peritoneal dialysis catheter, the adapter and the tubing of the dialysis sets are major determinants of dialysate flow rate².

The P/R ratio can be easily manipulated by changing the head height of the dialysate container, by lowering the drain bag, changing the diameter of the conduits (catheter, adapter, lines) or adding a pump for infusion (positive pressure) or drainage (negative pressure).

The further evolution in PD access design responded to the need for the largest practical internal diameter, kink prevention, obstruction prevention, reduction of inflammation through biocompatible materials and ease of implantation and removal.  This lead to a variety of designs with the following options:

• Curled vs. straight
• Column disc
• T-fluted
• Number of cuffs
• Cuff location
• Tunnel configuration (straight, swan-neck, pail-handle)
• Distal discs/balloons
• Materials (silicone rubber, polyurethane)

Photo courtesy of Dr. C. Cruz

In contrast to the great variety designs, only two materials have been used successfully in the manufacture of PD catheters.  Silicone rubber is the most frequently used plastic due to its relative biocompatibility, lack of trauma to surrounding tissues and minimal leeching of plasticizers.  Polyurethane allows thinner catheter walls with larger lumina because of its higher strength.  However, hydrolysis of the polyurethane surface and cracking of the material after exposure to polyethelene glycol or alcohol have been reported^3,4.

Catheter coatings with various materials with the aim of reducing infection have been tried.  Silver coated catheters have been shown to reduce colonization in animals, but not in humans⁵.  Antibiotic bonded catheters failed to reduce catheter related infections, possibly due to limited choice of antibiotics and short half-life of antibiotics⁶. 

It is of interest that despite the many design modifications and progress in biomaterials, even prospective randomized trials have failed to show any advantages of new catheter configurations over the traditional Tenckhoff design with respect to mechanical and infectious complications^7,8.  Catheter outcome is probably affected as much by operators experience and abilities and catheter care as by design or material.  The average catheter survival is better than 80% at one year and 70% at two years in experienced centers⁹.  A randomized study comparing straight and coiled Tenckhoff catheters found a significantly higher frequency of flow problems due to malposition requiring replacement of the catheter using the coiled catheter¹⁰.

References:

1. Tenckhoff H, Schechter H. A bacteriologically safe peritoneal access device. Trans Am Soc Artif Intern Organs 14:181-186, 1968
2. Cruz, C. The peritoneal dialysis catheter.  Seminars Dial 6:103-104, 1995
3. Cruz C. Clinical experience with a new peritoneal access device, in Ota K, Maher JF, Winchester JF, Hirszel P (eds): Current Concepts in Peritoneal Dialysis, Amsterdam, 1992, pp 164-169
4. Crabtree JH. Clinical biodurability of aliphatic polyether based polyurethanes as peritoneal dialysis catheters. ASAIO J 49:290-294, 2003   
5. Dasgupta MK. Silver-coated catheters in peritoneal dialysis. Perit Dial Int 17:S142-S145, 1997
6. Trooskin SZ, Harvey RA, Lennard TWJ, Greco RS.  Failure of demonstrated clinical efficacy of antibiotic-bonded continuous ambulatory peritoneal dialsysis (CAPD) catheters.  Perit Dial Int 10:51-59, 1990
7. Eklund BH, Honkanen EO, Kala AR, Kyllonen LE. Catheter configuration and outcome in patients on continuous ambulatory peritoneal dialysis:  a prospective comparison of two catheters. Perit Dial Int 14:70-74, 1994
8. Eklund BH, Honkanen EO, Kala AR, Kyllönen LE. Peritoneal dialysis access:  Prospective randomized comparison of the Swan neck and Tenckhoff catheters. Perit Dial Int 15:353-356, 1995
9. Golper TA, Brier ME, Bunke M, Schreiber MJ, Bartlett DK, Hamilton RW, Strife F, Hamburger RJ. Risk factors for peritonitis in long-term peritoneal dialysis:  The Network 9 peritonitis and catheter survival studies. Am J Kidney Dis 28:428-436, 1996
10.  Stegmayr BG, Wikdahl AM, Bergstrom M,  Nilsson C, Engman U, Arnerlov C, Peterson E. A randomized clinical trial comparing the function of straight and coiled Tenckhoff catheters for peritoneal dialysis.  Perit Dial Int  25:85-88, 2005