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Saudi Journal of Kidney Diseases and Transplantation
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REVIEW ARTICLE Table of Contents   
Year : 1994  |  Volume : 5  |  Issue : 1  |  Page : 23-27
CAPD - An Overview

Department of Medicine, School of Medicine & Dalton Research Center University of Missouri-Columbia, USA

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Keywords: CAPD, Peritoneal dialysis, Dialysis adequacy, Peritonitis, Swan neck catheter, Catheter Survival, Patient Survival.

How to cite this article:
Khanna R, Nolph KD. CAPD - An Overview. Saudi J Kidney Dis Transpl 1994;5:23-7

How to cite this URL:
Khanna R, Nolph KD. CAPD - An Overview. Saudi J Kidney Dis Transpl [serial online] 1994 [cited 2022 Oct 2];5:23-7. Available from: https://www.sjkdt.org/text.asp?1994/5/1/23/41357

   The global picture Top

At the end of 1993, nearly 80,000 patients were estimated to be on chronic peritoneal dialysis worldwide [1] , which represents about 14% of the dialysis population. The percentage of patients on chronic peritoneal dialysis in different countries range widely from 6% in Japan to 93% in Mexico [1] . Over two-thirds of them are on continuous ambulatory peritoneal dialysis (CAPD). Approximately 20% of the chronic peritoneal dialysis patients are on some form of cycler based automated peritoneal dialysis system [1] . The proportion of patients on cycler therapy is growing at a rate faster than CAPD.

   Survival on CAPD Top

Patient survival

A number of studies indicate that the actuarial survival rates, in comparable populations, are similar with CAPD and haemodialysis (HD) [2],[3],[4],[5],[6],[7],[8],[9],[10],[11],[12],[13],[14] . However, Maiorca and colleagues have observed that the relative risk of death may be higher in elderly patients on HD than on CAPD [6] . They also observed a more rapid increase in the relative risk of death for patients over the age of 53 years on HD than on CAPD [15] . On the contrary, a Cox proportional hazard model analysis of 4387 new endstage renal disease patients in the United States found a 14% greater risk of mortality for patients on CAPD than those on HD. The increased risk of death on CAPD was entirely accounted for by an increased risk of death for older diabetics on CAPD [16] . Interestingly, younger diabetics on CAPD had a lower risk of death when compared to HD. The analysis did not categorize in detail the severity of cardiac risk and thus, older diabetics on CAPD might have had more severe cardiac disease than older diabetics on HD. There was no consistent difference in death rates at different ages as a function of modality choice (HD vs. CAPD) for primary renal diseases other than diabetes [17] . Several studies in the past few years have not revealed modality choice as a significant risk factor [18],[19],[20] .

Technique survival

Technique survival generally implies the percentage of patients alive on their original dialysis treatment;death, transplantation and recovery of renal function are considered a loss to risk. In essence, a technique failure represents transfer to another form of dialysis treatment. Technique survivals on CAPD have usually been lower than HD primarily because of a high incidence of peritonitis in the era of standard connectology [2],[3],[4],[5],[6],[11],[13],[14] . The recent improvement in the incidence of peritonitis, due mainly to the introduction of Y-set, has resulted in a significantly improved technique survival rate of 77.4% for CAPD patients [21] . An Italian study made a similar observation and speculated that elimination of peritonitis should eventually result in comparable technique survivals for both HD and CAPD patients [22] .

Catheter survival

The swan neck catheter with a permanent bend in the intercuff segment, has shown a survival rate of 73% at three years, a rate considerably better than the 30% reported previously by the United States CAPD registry [23] . The swan neck catheter was designed to provide a downward exit hole to reduce the risk of exit-site infection and a caudal direction to the intraperitoneal. segment of the peritoneal catheter on insertion to reduce the risk of catheter tip migration out of the pelvic space. Additionally, the permanently moulded bend in the catheter eliminates the resilient force, and thus lowers the risk of external cuff extrusion. Use of swan neck catheters has essentially eliminated these above mentioned complications. A recent survey indicates its use of over 30 percent of all the new catheters inserted world over [24] .

Peritoneal membrane stability

The recent peritoneal biopsy registry report suggests that the peritoneal membrane undergoes minimal or no morphological change for up to seven years, in the absence of peritonitis in patients on CAPD [25] . The changes noted vary from minimal changes to loss of mesothelium with hyalinized stroma and a striking acellular structure (cellular desert). The collagen in the stroma undergoes a change in texture and orientation. The peritoneum attains brownish discoloration with a leathery appearance. Cellular infiltration is sparse, distributed in the stroma and around the perivascular location, and the microvilli are lost. The rough endoplastic reticulum is hyperplastic and the occurrence of peritoneal fibrosis is an all or none phenomenon. The diabetiform changes in the peritoneal capillary basement membrane in non-diabetic patients appear only in those who experience peritonitis. It is hypothesized that the breakdown of the mesothelial barrier during peritonitis results in an increased permeability to high concentrations of glucose in the peritoneal interstitium and the glycosylation of the capillary basement membranes. The technique of autologous mesothelial cell transplantation in animals and patients is an attempt to re-mesothelialize the peritoneum after peritonitis [26] . Sequential measurements of solute clearances and mass transfer co-efficients in patients on CAPD for up to five to six years have shown no changes from baseline measurements [27] .

   Peritoneal dialysis adequacy and nutrition Top

To achieve comparable clinical outcomes, greater small solute clearances are required by haemodialysis than CAPD. To explain this difference, the peak concentration hypothesis proposes that for comparable protein intake by HD and CAPD patients, weekly HD requires at least one and a half times more weekly urea clearance than does CAPD, in order to maintain the peak pre- HD blood urea nitrogen (BUN) levels below the steady state BUN levels of CAPD [28],[29] . With the same protein intake, protein catabolic rate (PCR) and weekly urea clearances, the BUN levels in patients on three-times-weekly HD would be higher than CAPD steady state levels. In that case, and if BUN were a marker of small molecular weight toxin that suppresses appetite, then HD patients are clearly under-dialyzed and should manifest loss of appetite and a lower PCR unless weekly urea clearances were increased well above those of CAPD. The peak concentration hypothesis is supported by several recent studies that found at the same Kt/V, the urea clearance normalized to total body water, CAPD is indeed associated with a higher PCR than HD [30],[31],[32],[33] . We, at the University of Missouri try to maintain a PCR per normalized body weight of 0.9 or higher per day in CAPD patients. Each CAPD patient's weekly urea clearance is followed along with a weekly creatinine clearance. We have found that in most patients, to maintain the target PCR of 0.9gm/kg/day, a weekly urea Kt/V of 1.7 and a weekly creatinine clearance of 50 liters per 1.7 m2 body surface area is required. It is important to add the contribution of the residual renal function to the total solute clearance. Thus, the average of renal urea and creatinine clearances is added to the dialysate clearance to estimate the total clearance.

The monitoring of dialysis adequacy in each patient includes initial as well as periodic assessment of peritoneal membrane transport characteristics using the peritoneal equilibration test (PET) [34] and weekly urea Kt/V and creatinine clearance. Adjustment in dialysis prescriptions are made to meet the adequacy standards as residual renal function declines and peritoneal membrane function changes.

   Peritonitis and exit-site infection Top

Recent introduction and widespread use of disconnect devices have resulted in consistent reduction in the incidence of peritonitis to about one episode every 24 patient months [35] . The key innovation that has contributed to such dramatic improvement in the peritonitis rate is the Y-set wherein, a flushing of the system with dialysis solution followed by drainage from the peritoneal cavity after connection is performed, before fresh solution is instilled. The use of in line disinfectant is optional in this system. It is currently believed that the simple straightline spike system is being used by approximately 27%, a disposable disconnect system by about 31%, an ultraviolet device by 12%, a reusable Y-set by 48%, an ultraviolet disconnect system by 3% and a twin bag by about 10% of the people.

The United States Renal Data System report indicates that the risk of peritonitis has been reduced by 40% with the Y-set use [21] . The relative risk of first peritonitis was 0.6 compared to the standard system. The relative risk for standard ultraviolet system was 0.75. The average number of months between episodes of peritonitis was 9.0 with the standard system, 15 with the Yset, and 13.9 with the standard ultraviolet system.

A detailed classification of exit-site infection has been recently proposed [36] . Identification of early acute infection and traumatized exit-site may permit timely initiation of treatment and effective cure. Catheter immobilization and sterile dressings in the first 6 weeks after catheter insertion may favor better healing of exit-site by permitting in growth of epidermis into the sinus tract towards the superficial cuff. The nasal carriage of Staphylococcus aureus Scientific Name Search  may predispose to exit-site infections. Prophylactic therapy with agents such as rifampicin may reduce the incidence of exit-site infections in these nasal carriers [37],[38],[39],[40] .

   Preservation of residual renal function Top

Several retrospective and prospective studies suggest that residual renal function is preserved for a period longer in CAPD patients than HD [41],[42] . This may relate to rapid decline in residual nephron function in HD patients due to fluctuations in glomerular capillary pressure and the action on the glomerular epithelium of inflammatory mediators released into the blood by the blood membrane interaction.

   References Top

1.Woodworth W. Baxter Worldwide Overview, Deerfield, II, 1992.  Back to cited text no. 1    
2.Nolph KD. Comparison of continuous ambulatory peritoneal dialysis andhemodialysis. Kidney Int Suppl 1988;24S:123-31.  Back to cited text no. 2    
3.Nolph. KD. Clinical results with peritoneal dialysis-registry experiences. In: Twardowski ZJ, Nolph KD, Khanna R, et al. (eds).Contemporary issues in Nephrology. New York: Churchill Livingston, 1990;127-44.  Back to cited text no. 3    
4.Maiorca R, Cancarini GC, Camerini C, et al. Is CAPD competitive with haemodialysis for long-term treatment of uraemic patients? Nephrol Dial Transplant 1989;4:244-53.   Back to cited text no. 4  [PUBMED]  [FULLTEXT]
5.Disney APS, (ed). Twelfth report of the Australian and New Zealand Combined Dialysis and Transplantation Registry. Woodville, South Australia: Queen Elizabeth Hospital, 1989.  Back to cited text no. 5    
6.Maiorca R, Vonesh E, Cancarini GC, et al. A six-year comparison of patient and technique survivals in CAPD and HD. Kidney Int 1988;34: 518-24.  Back to cited text no. 6  [PUBMED]  
7.Wolfe RA, Port FK, Hawthorne VM, Guire KE. A comparison of survival among dialytic therapies of choice: in-center haemodialysis versus continuous ambulatory peritoneal dialysis at home. Am J Kidney Dis 1990;15:433-40.  Back to cited text no. 7  [PUBMED]  
8.Cavalli PL, Viglino G, Goia F, et al. CAPD versus haemodialysis: 7 years of experience. Adv Perit Dial 1989;5:52-5.  Back to cited text no. 8  [PUBMED]  
9.Disney APS (ed). Thirteenth report of the Australia and New Zealand Dialysis and Transplantation Registry. Woodville, South Australia: Queen Elizabeth Hospital, 1990.  Back to cited text no. 9    
10.Maiorca R, Vonesh E, Cavalli PG, et al. A multi-center selection-adjusted comparison of patient and technique survivals on continuous ambulatory peritoneal dialysis and haemodialysis (abstract). Abstracts of the Fifth Congress of the International Society of Peritoneal Dialysis 1990;5:31.   Back to cited text no. 10    
11.Posen GA, Rappaport A, Lucas D, (eds).The Canadian Renal Failure Registry 1986 Report. Ottawa, Canada, 1987.  Back to cited text no. 11    
12.Golper TA, Greetings W, Selwood NH, et al. (eds). Peritoneal dialysis results in the EDTA Registry, In: Nolph KD, (ed). Peritoneal Dialysis. 3rd ed. Boston; Kluwer Academic. 1988:414.  Back to cited text no. 12    
13.Gokal R. Worldwide experience, cost effectiveness and future of CAPD-its role in renal replacement therapy. In: Gokal R, (ed). Continuous ambulatory dialysis. Edinburgh:Churchill Livingstone, 1986:349.  Back to cited text no. 13    
14.Maiorca R, Cancarini G, Manili L, Camerini C, Brunori G. Life table analysis of patient and method survival in continuous ambulatory peritoneal dialysis and haemodialysis after six years' experience. In: Khanna R, Nolph KD, Prowant BF, et al. (eds). Advances in CAPD. Toronto: University of Toronto. Press, 1986:27.   Back to cited text no. 14    
15.Maiorca R, Vonesh EF, Cavalli P, et al. A multi-center, selection-adjusted comparison of patient and technique survivals on CAPD and haemodialysis. Perit Dial Int 1991;11: 118-27.  Back to cited text no. 15  [PUBMED]  [FULLTEXT]
16.Held PH, Port FK, Gaylin DS, et al. Evaluation of initial predictors of mortality among 4387 new ESRD patients: The USRDS case mix study (Abstract) J Am Soc Nephrol1991;2:328.  Back to cited text no. 16    
17.US Renal Data System. USRDS 1991 Annual Data Report. The National Institute of Health, National Institute of Diabetes and Digestive and Kidney Diseases. Bethesda, MD, 1991.  Back to cited text no. 17    
18.Lunde NM, Port FK, Wolfe RA, Guire KE. Comparison of mortality risk by choice of CAPD versus haemodialysis among elderly patients. Adv Perit Dial 1991;7:68-72.  Back to cited text no. 18  [PUBMED]  
19.Gentile MA, Carriazo A, Pavon MI et al. Comparison of survival in continuous ambulatory peritoneal dialysis and hospital haemodialysis: a multi-center study. Nephrology Dial Transplant 1991;6:444-51.  Back to cited text no. 19    
20.Nelson CB, Port FK. Dialysis patient survival: evaluation of CAPD versus haemodialysis using three techniques. Abstracts, 12th annual peritoneal dialysis conference. Perit Dial Int 1992; (suppl 1):144,  Back to cited text no. 20    
21.Port FK, Held PJ, Nolph KD, Turenne MN, Wolfe RA. Risk of peritonitis and technique failure by CAPD connection technique: a national study. Kidney Int 1992;42:967-74.  Back to cited text no. 21  [PUBMED]  
22.Maiorca R, Cancarini GC, Manili M, Canerini C, Brunori G. Peritonitis rate and CAPD results. In: La Greca G, Ronco C, Feriani M et al (eds). Peritoneal Dialysis: Proceedings of the fourth international course on peritoneal dialysis. Milano: Wichtig Editore, 1991:223-31.  Back to cited text no. 22    
23.Twardowski ZJ, Prowant BF, Khanna R,Nichols WK, Nolph KD. Long-term experience with swan neck Missouri catheters. ASAIO Trans; 1990;36: 491-4.  Back to cited text no. 23    
24.Twardowski ZJ, Nolph KD, Khanna R,Prowant BF. Computer interactive session:Catheters. Advances in Peritoneal Dialysis Vol. 10 (In Press)  Back to cited text no. 24    
25.Dobbie JW, Lloyd JK Gal CA. Categorization of ultrastructural changes in peritoneal mesothelium, stroma and blood vessels in uremia and CAPD patients. Adv Perit Dial. 1990;6:3-12.  Back to cited text no. 25    
26.Di Paolo N. Tissue culture and autologous implantation of mesothelial cells. In: La Greca G, Ronco C, Feriani et al. (eds), Peritoneal Dialysis: Proceedings of the fourth international course on peritoneal dialysis Milano, Wichtig Editore, 1991:19-31.  Back to cited text no. 26    
27.Struijk DG, Krediet RT, Koomen GCM, Boeschoten EW, Hock FJ, Arisz L. Prospective longitudinal follow-up of peritoneal transport characteristics in CAPD patients. In: Struijk DG (ed). Peritoneal transport in CAPD patients. Druk: Krips Repro Meppol 1992;133-50.  Back to cited text no. 27    
28.Keshaviah PR, Nolph KD, Van Stone JC. The peak concentration hypothesis: a ureakinetic approach to comparing the adequacy of continuous ambulatory peritoneal dialysis(CAPD) and haemodialysis. Perit Dial Int1989;9:257-60.  Back to cited text no. 28  [PUBMED]  [FULLTEXT]
29.Gotch FA. The application of urea kinetic modeling to CAPD. In: La Greca G, Ronco C,Ferriani M, et al. Peritoneal dialysis: Proceedings of the fourth international course on peritoneal dialysis. Milano, Wichtig editore,1991:47-51.  Back to cited text no. 29    
30.Bergstrom J, Alvestrand A, Lindhom B, Tranaeus A. Relationship between KT/V and protein catabolic rate is different in continuous ambulatory dialysis and haemodialysis patients (abstract) J Am Soc Nephrol 1991;2:358.  Back to cited text no. 30    
31.Keshaviah PR, Nolph KD, Prowant B, et al. Defining adequacy of CAPD with urea kinetics. Adv Perit dial 1990;6:173-7.  Back to cited text no. 31  [PUBMED]  
32.Delmez JA, Windus DW. Haemodialysis prescription and delivery in a metropolitan community. he St. Louis Nephrology Study Group. Kidney Int 1992;41:1023-28.  Back to cited text no. 32    
33.Twardowski ZJ. PET-a simpler approach for determining prescriptions for adequate dialysis therapy. Adv Perit Dial 1990;6:186-91.  Back to cited text no. 33  [PUBMED]  
34.Viglino G, Cantaluppi A, Gandolfo C,Peluso F,Cavalli PL. Y-set evolution. In: La Grecca G, Ronco C, Feriani M, et al. (eds). Peritoneal Dialysis: Proceedings of the fourth international course of peritoneal dialysis. Milano: Wichtig Editore, 1991:281-93.  Back to cited text no. 34    
35.Twardowski ZJ, Dobbie JW, Moore HL, etal. Morphology of the peritoneal dialysis tunnel: Proceedings of the fourth international course of peritoneal dialysis. Milano: Wichtig Editors, 1991:241-5.  Back to cited text no. 35    
36.Swartz R, Messana J, Starmann B, Weber M, Reynolds J. Preventing Staphylococcus aureus infection during chronic peritoneal dialysis, J Am Soc Nephrol 1991 ;2:1085-91.   Back to cited text no. 36    
37.Luzar MA, Coles GA, Faller B, et al. Staphylococcus aureus nasal carriage and infection in patients on continuous ambulatory peritoneal dialysis. N Eng J Med 1990;322:505-9.  Back to cited text no. 37    
38.Luzar MA, Brown CB, Balf D, et al. Exit site care and exit-site infection in continuous ambulatory peritoneal dialysis CAPD: results of a randomized multicenter trial. Perit Dial Int 1990;10:25-9.   Back to cited text no. 38  [PUBMED]  [FULLTEXT]
39.Zimmerman SW, Ahrens E, Johnson CA, et al. Randomized controlled trial of prophylactic rifam-picin for peritoneal dialysis related infections. Am J Kidney Dis 1991;IS:225-31.   Back to cited text no. 39    
40.Rottenberg J, Issad B, Gallego JL, et al. Evolution of residual renal function in patients under going maintenance haemodialysis or continuous ambulatory peritoneal dialysis. Proc Eur Dial Transplant Assoc 1983;19:397-403..   Back to cited text no. 40    
41.Rottenberg J, Issad B, Poignet JL, et al. Residual renal function and control blood glucose levels in insulin dependent diabetes mellitus patients treated by CAPD. In: Keen H, Legrain M. eds. Prevention and treatment of diabetic nephropathy, Boston: M&P Press, 1983;339-52.   Back to cited text no. 41    
42.Cancarini GC, Brunori G, Camerini C, et al. Renal function recovery and maintenance of residual diuresis in CAPD and haemodialysis. Perit Dial Bull 1986:6:76-9.  Back to cited text no. 42    

Correspondence Address:
Ramesh Khanna
Department of Medicine, MH 436 School of Medicine, University of Missouri-Columbia, Missouri
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Source of Support: None, Conflict of Interest: None

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