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New Technologies in Peritoneal Dialysis


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New Technologies in Peritoneal Dialysis

  1. 1. CJASN ePress. Published on March 21, 2007 as doi: 10.2215/CJN.03331006 Mini-Review New Technologies in Peritoneal Dialysis Joanne M. Bargman University Health Network, Toronto, Ontario, Canada In recent years, there have been some interesting advances in the science and practice of peritoneal dialysis (PD). This review focuses on selected technological advances and the impact that these changes may have on this modality. New, so-called “biocompatible” fluids have more physiologic pH and reduced glucose degradation products. These new fluids may reduce the deleterious effects of chronic exposure to the peritoneal membrane. However, enthusiasm for these new fluids is outstripping rigorous evidence that they change patient outcome. Continuous-flow PD offers a way to increase dramatically small solute clearance. However, there are significant technological barriers to the implementation of this kind of dialysis. Furthermore, there is little evidence that augmented small solute clearance will improve survival in PD patients. Finally, new catheter insertion techniques provide perhaps the most practical advances in allowing successful commencement of this excellent home dialysis modality. Clin J Am Soc Nephrol ●●: ●●●-●●●, ●●●●. doi: 10.2215/CJN.03331006 S ince the publication in 1978 of a method of continuous Biocompatible Solutions peritoneal dialysis (PD) in the ambulatory patient, PD Standard peritoneal solutions must be manufactured in a has been successful as a simple, economical, and effec- way that the product will remain stable with a practicable shelf tive way to treat stage 5 chronic kidney disease (1). A number life. Because the solution is very high in glucose, a major of important innovations in therapy have occurred along the byproduct of this solution is the formation of glucose degrada- way. The introduction of the “Y-set” catheter connection, in- tion products (GDP). These comprise a family of compounds corporating the technology of flushing the tubing lumen before with known or suspected adverse consequences, both at the infusing dialysate into the patient after connection, was instru- level of the peritoneal membrane and also systemically, via mental in reducing the incidence of PD peritonitis and was a absorption from the peritoneal cavity (4). The GDP can also link significant advance in the therapy (2,3). The popularization of with proteins, leading to the formation of advanced glycosyla- nighttime exchanges by an automated cycler system freed the tion end products. An ambient acidic pH will reduce the for- patient from the constraint of having to perform several ex- mation of GDP in the bag of dialysate, and for this reason, the changes during the day. Furthermore, the dosage of dialysis pH of unused peritoneal dialysate is approximately 5.2. An- could be adjusted more finely with the cycler, with modifiable other challenge with formulating peritoneal dialysate for stor- age is that bicarbonate cannot be used as the buffer, because it variables including dialysate dwell volume, number of ex- has the potential to react with calcium in the dialysate and form changes, dwell times, and total overnight treatment times. calcium-carbonate precipitates. Therefore, lactate is used in lieu Rapid transporters who had problems with fluid removal on of bicarbonate and is rapidly and successfully converted into conventional continuous ambulatory PD (CAPD) because the bicarbonate in vivo. Given the acid pH (but not sufficiently longer dwells of CAPD were associated with rapid glucose acidic to halt completely the formation of GDP), high lactate, absorption, dissipation of the osmotic gradient, and poor ultra- and absent bicarbonate, peritoneal dialysate is not completely filtration could now be more successfully ultrafiltered with the physiologic, or “biocompatible.” A number of studies using shorter dwell cycles on the automated PD. both in vivo and in vitro methods have suggested that the There have been some interesting developments in both tech- standard dialysate is associated with depletion of mesothelial nique and technology in recent years, and these are reviewed. cells that line the peritoneal cavity, thickening of the membrane These include new, so-called “biocompatible” PD solutions, itself, and the development of a unique vasculopathy of the continuous-flow PD (CFPD), and new PD catheter placement vessels in the peritoneal interface (5–7). It has been postulated strategies, including laparoscopic placement and the “buried that nonphysiologic components of the dialysate, in inducing catheter” technique. these anatomic changes, may ultimately lead to the develop- ment of rapid-transport status and ultrafiltration failure that is seen in a subset of long-term PD patients. This observation has prompted the ingenious development Published online ahead of print. Publication date available at of PD solutions that have been labeled as “biocompatible.” The dialysate is divided into at least two subcompartments. One Address correspondence to: Dr. Joanne M. Bargman, University Health Network, 200 Elizabeth Street 8N-840, Toronto, Ontario M5G 2C4, Canada. Phone: 416-340- compartment contains the glucose and the electrolytes. This 4804; Fax: 416-340-4999; E-mail: subcompartment has a very low pH, which slows the formation Copyright © ●●●● by the American Society of Nephrology ISSN: 1555-9041/●●●●–0001
  2. 2. 2 Clinical Journal of the American Society of Nephrology Clin J Am Soc Nephrol ●●: ●●●-●●●, ●●●● of GDP. The other compartment contains bicarbonate or a glycosylation end products, extrapolating this to preservation bicarbonate-lactate mixture. Because the calcium is stored in the of residual renal function and prolongation of life still remains glucose-containing compartment, separated from the buffer, a big leap. Early findings of reduction in peritonitis have not there is no risk for calcium-bicarbonate interaction during stor- been reproduced (10,12). It is still too early to know whether the age. Before the dialysis exchange, the patient breaks a frangible new solutions will delay the development of late ultrafiltration connection that separates the two compartments, and when the failure in long-term PD patients. Finally, because a rapid-trans- components are mixed, the final pH is close to physiologic. The port state is associated with inflammation and vasodilation of patient now infuses a normal-pH, low-GDP, bicarbonate-con- vascular beds in the peritoneum, the increase, rather than de- taining solution. crease, in transperitoneal solute flux with these new solutions Although it seems reasonable to presume that infusion of remains a concern. However, there is still a sound physiologic dialysate with a more physiologic composition should be a underpinning to the design of the newer solutions. What is good thing, results have been variable and driven at times more needed, however, are rigorous controlled trials to prove that by enthusiasm than by science. Initial reports suggested that biocompatibility translates into better patient outcomes. these solutions were associated with less infusion pain (8,9). A major, well-conducted, randomized, controlled, crossover trial CFPD found, in a secondary end point, that urine volume and resid- Patients who are on conventional hemodialysis can have ual renal GFR increased when the patient was using the bio- their solute clearance augmented via multiple mechanisms, in- compatible dialysis fluid and decreased with the standard di- cluding increasing the blood flow, dialysate flow, ultrafiltra- alysate (10). Indeed, in this crossover format, the patients who tion, or time on dialysis. Conversely, patients who are on PD started with the standard solution had an increase in urine are more limited with respect to maneuvers to increase solute volume when crossed over to the biocompatible dialysis fluid. clearance. For patients who are already undergoing dialysis 24 These results were interpreted as showing that the biocompat- h/d, there is obviously no room to increase time on dialysis. ible fluid “preserved” residual renal function. What is not Increasing the volume of dialysate will augment small solute appreciated in this study, however, is that there was a change clearance but is limited by the concomitant increase in intra- in the peritoneal transport characteristics associated with the abdominal pressure. Blood flow to the peritoneum cannot be new solutions. Indeed, the so-called biocompatible solution significantly manipulated. There remains only the variable of was associated with a change to a more rapid transporter dialysate flow. Small solute clearance will increase with in- phenotype, with consequent reduction in ultrafiltration of 350 creasing dialysate flow. This observation is the rationale for the ml/d. (It is relevant to remember that one explanation for the development of CFPD. Originally described by Shinaberger et higher incidence of congestive heart failure in the control group al. (13), there is a continuous flow-through of dialysate into and in the Adequacy of Peritoneal Dialysis in Mexico [ADEMEX] out of the peritoneal cavity. This technique requires either two trial was a reduction in ultrafiltration of approximately 100 PD catheters or a double-lumen catheter. Dialysate is infused ml/d.) The contribution of this reduced ultrafiltration and through one port and is simultaneously drained from the sec- change in volume status to the increase in residual renal func- ond. Theoretical advantages of CFPD include continuous con- tion is unclear. tact of the dialysate with the dialyzing membrane so that there Two recent reports from Korea examined survival in PD is no lost time for inflow and outflow. In addition, the concen- patients who underwent dialysis with conventional versus tration gradient for solute diffusion into the dialysate fluid will newer neutral-pH solutions. Importantly, these were not ran- be maintained over time, because the dialysate-to-plasma ratio domized studies, and what determined which patients received will no longer approach unity for small solutes such as urea, as which solution is not stated. Nevertheless, patients who under- it does with the typical “dwell” on conventional PD. Another went dialysis with the biocompatible dialysate lived longer advantage with the continuous-flow system is that glucose will compared with those who did not (11,12). There were differ- be continuously replenished in the dialysate. Therefore, the ences in center characteristics between the two groups, and the glucose concentration gradient and, hence, the osmotic gradient younger age of the group that received the biocompatible dia- will remain intact, leading to enhanced ultrafiltration. lysate alone accounted for half of the mortality difference. Another advantage is that the dialysate could be generated Furthermore, a very long-living subset of patients who started by an on-line apparatus, which would allow for the production therapy on standard solutions and were switched to the newer of more biocompatible fluids. Using this on-line process, less solutions were correctly included as part of the standard group modification of the PD fluid would be needed for storage and in the intention-to-treat analysis in the first publication (11) but shelf life (discussed in the previous section). Therefore, the removed from the analysis altogether in the second report (12). real-time generation of dialysate would allow for bicarbonate- This can lead to a major problem of confounding by indication, based dialysate with physiologic pH. Another putative advan- in that the physicians may decide to “invest” in the healthier tage is that if blood purification could be achieved in a shorter patients and switch them over to the newer, expensive PD period of time, then the abdomen could be left dry for several solutions. hours a day, allowing for repair and replenishment of the It is still relatively early for the biocompatible solutions. normal intraperitoneal structures (14). Although these solutions could lead to less damage by GDP Early trials of CFPD suggested that with dialysate flow rates and a small relative reduction in circulating levels of advanced between 120 and 300 ml/min, urea clearance could be as high
  3. 3. Clin J Am Soc Nephrol ●●: ●●●-●●●, ●●●● New Technologies in PD 3 as 125 ml/min (15). Other studies have reported that the mean ated barriers to the use of PD: Primary catheter dysfunction and creatinine clearance more than doubled compared with con- the “crash start” patients on hemodialysis. ventional automated PD and was five-fold greater than with CAPD (16). New PD Catheter Placement Techniques Insertion under Laparoscopic Visualization Although it is difficult to document, a nonfunctioning or The Faulty Rationale for CFPD poorly functioning PD catheter is a major cause of technique Although at first glance the dramatic increase in small solute failure and a hindrance to the establishment of a successful PD clearance is appealing, it is important to remember that higher program. Whereas hemodialysis has the tunneled or nontun- peritoneal small solute clearance has not been associated with a neled internal jugular line as a default option for the patient survival benefit in PD (17,18). PD treats chronic kidney disease who is unable to maintain a fistula or a graft, there is no in a manner that is different from that of hemodialysis and is equivalent for the PD patient, who will then be forced to change poorly estimated or quantified by small solute kinetics such as dialysis modality. Kt/V urea. This is evidenced by the weekly Kt/V urea in PD, Options for placement techniques include conventional sur- which is approximately half as much as that on hemodialysis yet gical insertion, insertion under peritoneoscopic or laparoscopic is associated with comparable survival to that on HD (19 –21). guidance, “blind” insertion, and radiologic insertion with flu- Benefits of PD likely relate to preservation of residual kidney oroscopy. It has been considered that the particular method of function, clearance of middle and larger molecular weight ure- insertion is not as important for the success of the catheter as mic toxins (via both the peritoneal membrane and the residual much as the experience and the interest of the operator per- kidney function), and the “continuousness” of the dialysis. forming the insertion. Because the nephrologist has an interest Indeed, with respect to the continuous nature of PD, leaving the in the success of the catheter, it is not surprising that good CFPD patient dry during part of the day because of “enough” results have been reported with the techniques when the neph- small solute clearance during the procedure may do the patient rologist performs the procedure (27). However, many neph- a disservice. That kind of regimen will turn a continuous dial- rologists do not have the time, training, or inclination to insert ysis process into an intermittent one, and the benefit of the peritoneal catheters. In that case, the insertion usually falls to a continuousness will be lost. In addition, removal of middle surgeon. Again, results may be predicated on the interest or the molecular weight uremic toxins is time dependent and thus experience of the surgeon. In addition, blind surgical placement proportional to the total number of hours on dialysis. Using can be hampered by stool-filled bowel, a lively omentum, and CFPD for just part of the day would likely impair removal of bowel adhesions. these toxins. Indeed, one analysis suggested no major increase Insertion of the dialysis catheter under direct visualization by in middle molecule clearance, even using CFPD in combination laparoscopy affords a number of advantages. The operator can with CAPD dwells for the rest of the 24-h cycle (22). It follows, ensure, in real time, that the catheter tip is placed in the deep therefore, that a regimen such as CFPD for 8 h, with no dialysis pelvis. Adhesions can be lysed during the procedure, and a for the other 16 h, would compromise daily middle molecule large, redundant omentum can be tacked up into the upper clearance. abdomen (“omentopexy”) to prevent it from wrapping around The use of CFPD to augment small solute clearance seemed the catheter tip in the pelvis. Furthermore, the part of the rational when it was believed that higher small solute clearance catheter that traverses the rectus sheath in the abdominal wall was associated with increased survival in PD patients (23). can be tunneled superinferiorly so that the catheter has a “built- Some studies, however, have not shown this to be the case in” directionality into the pelvis and decreases the chances of its (24 –26). There may be other advantages to CFPD, such as flipping into the middle or upper abdomen (Figure 1). enhanced ultrafiltration, but it cannot be promoted solely on the basis of achieving a higher Kt/V urea. There are consider- able technologic challenges with this process also, including designing double-lumen catheters, avoiding streaming or recir- culation with these catheters, and, of course, technology to match inflow to outflow to maintain a constant intraperitoneal pressure. The mechanics of these innovations should be prac- ticable in the future, and certainly on-line generation of the peritoneal dialysate is an attractive alternative to the delivery, storage, and hanging of bags of fluid. What remains to be determined, however, is whether these innovations improve patient outcome. The benefit of biocompatible dialysate and the technique of Figure 1. As a result of rectus sheath tunneling, the catheter has CFPD are, as mentioned, unproved. In contrast, more “low- a “built-in” directionality toward the pelvis. In contrast, if the tech” innovations with respect to the placement of the dialysis catheter is inserted at right angles to the surface, then it will be catheter are now in use in many centers. These techniques can more prone to migrate into the middle and upper abdominal be helpful in addressing important but perhaps underappreci- quadrants. Courtesy of Dr. J. Crabtree (28).
  4. 4. 4 Clinical Journal of the American Society of Nephrology Clin J Am Soc Nephrol ●●: ●●●-●●●, ●●●● Excellent results have been reported with the insertion tech- the intraperitoneal portion of the catheter. There have been niques using direct visualization. Crabtree et al. (28) noted very previous reports of these complications with the embedded high rates of primary and long-term function with laparoscopic technique (33). However, with careful attention to these issues placement of peritoneal catheters, compared with their experi- during the implantation, the buried technique can be a useful ence with the blind surgical technique. Conversely, others have way to secure peritoneal access ahead of time so that the patient had very good experience with blind placement or placement can start either electively or urgently with this modality, rather with the aid of a peritoneoscope (where placement and visual- than risking interim insertion of a temporary hemodialysis ization can be done only in sequence, not simultaneously). catheter (34). Furthermore, the literature has been contradictory in terms of comparisons between laparoscopic and surgical insertions Conclusion (29,30). A recent review and meta-analysis of randomized trials The past few years have seen a number of advances in the that compared laparoscopy with laparotomy reported no sig- technical aspects of PD. However, there has been little in the nificant difference in peritonitis, catheter replacement, or tech- way of rigorous studies to prove whether they will have an nique failure (31). In the final analysis, the most important impact on outcome. There are challenging technological barri- predictor of successful catheter implantation is likely having an ers to the implementation of CFPD, in conjunction with ques- operator who is committed to and engaged in the procedure. tions about the ultimate benefit of this modality. The enthusi- Nonetheless, the laparoscopic technique affords the surgeon a asm for new, so-called biocompatible dialysis solutions has, so greater degree of visualization and control over the proper far, outpaced proof that these solutions are actually beneficial placement of the catheter and the opportunity to deal with (35). There is an urgent need for well-conducted studies to impediments such as intraperitoneal adhesions. demonstrate benefit of the new solutions. Perhaps the greatest cause for enthusiasm lies in innovations in methods of catheter Buried Peritoneal Catheters implantation, so as to prevent the disheartening experience of Another relatively new technique is that of “burying” the primary nonfunction of the peritoneal catheter. The function of distal end of the newly implanted PD catheter subcutaneously the peritoneal catheter remains an important hurdle in the so that no part of the catheter is extracutaneous. The original successful implementation of this excellent form of renal re- intent of this technique, proposed by Moncrief et al. (32), was to placement therapy. allow complete healing of the catheter tunnel in a sterile envi- ronment. By avoiding unintended bacterial inoculation of the Disclosures catheter, exit site, or tunnel, a germ-free seal could be formed None. during the wound healing. After a period of time, originally proposed as 3 to 5 wk, the distal end of the catheter could be externalized. 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