Peritoneal dialysis modifications to avoid CAPD drop-out

Zbylut J. Twardowski, Ramesh Khanna, Karl O. Nolph

Modifications of peritoneal dialysis such as continuous cyclic peritoneal dialysis (CCPD) nightly peritoneal dialysis (NPD). daytime ambulatory peritoneal dialysis (DAPD ), and high volume peritoneal dialysis, allow continuation of peritoneal dialysis therapy in patients who experience inadequate dialysis or inadequate ultrafiltration on a standard CAPD.

Patients with complications related to increased intraabdominal pressure, such as hernias, hemorrhoids, and abdominal leaks benefit from peritoneal dialysis performed in the supine position.

The peritoneal transport rate is an important factor which determines the patient response to various forms of peritoneal dialysis. Patients with high average peritoneal solute transport do well on standard CAPD even after losing residual renal function. Patients with high peritoneal solute transfer rates are likely to have inadequate ultrafiltration on standard CAPD. These patients do much better on dialysis modalities with short dwell exchanges, i.e.NPDorDAPD. Patients with low and low average peritoneal transport rates are likely to develop symptoms and signs of inadequate dialysis on standard CAPD as residual renalfunction becomes negligible, and may require high efficiency peritoneal dialysis modalities.

From the Division of Nephrology, Department of Medicine, University of Missouri, Veterans Administration Hospital, Dalton Research Center, Columbia, Missouri 65212. Supported in part by Nephrology Research Fund.


Standard continuous ambulatory peritoneal dialysis (CAPO) with four 2 L exchanges is the most widely used peritoneal dialysis modality at present; however, after 2 years of therapy about 34% of patients are transferred from CAPO. Over 70% of transfers are related to medical and psychosocial problems (1).

The purpose of this paper is to present our management of patients who would transfer from CAPO because of complications related to high intra abdominal pressure, inadequate dialysis, and inadequate ultrafiltration .

Such patients may be managed on other peritoneal dialysis modalities. At present less than half of our patients remain on standard CAPO with four 2 L exchanges.

Intra abdominal pressure and choice of peritoneal dialysis

Elevated intra abdominal pressure predisposes to hernias, abdominal dialysate leaks, hemorrhoids, bladder prolapse, and abdominal discomfort with loss of appetite. Intra abdominal pressure is markedly higher in the vertical position than in the supine position (2). The pressure is directly proportional to the intraperitoneal fluid volume and increases with activities such as walking, jogging, jumping, bicycling, and particularly with weight lifting, coughing, and straining (3).

For patients with complications related to high intra abdominal pressure the most suitable regimen is a supine peritoneal dialysis where the patient is recumbent while there is intraperitoneal fluid. In our institution the supine peritoneal dialysis is performed every night with an intermittent technique and is called nightly intermittent peritoneal dialysis (NIPO). Continuous cyclic peritoneal dialysis (CCPO) with decreased daytime fluid volume has been recommended for such patients by others (4,5). The obvious advantage ofNIPO over CCPO in such patients is complete elimination of daytime exchanges. The lower dialysis efficiency due to decreased dialysis time must be compensated by longer nightly dialysis in some patients.

Some patients prefer NIPD over CAPD or CCPD because of distorted body image due to a protruding abdomen related to the presence of intraperitoneal fluid during the daytime.

To achieve adequate dialysis and good blood pressure control the variables such as length of dialysis, frequency of exchanges, and dialysis solution sodium concentration must be adjusted according to the patients' peritoneal transport characteristics.

Adequacy of dialysis and ultrafiltration, peritoneal membrane transport, and choice of dialysis therapy

The ultimate goal of any dialysis therapy is to achieve adequate dialysis and ultrafiltration. Although there is not a general agreement on the definition of these terms, in our institution the following definitions are accepted:

Adequate dialysis

The patients are considered as adequately dialyzed if they feel well, have a good appetite, no symptoms or signs of uremia, maintain hematocrit above 25% (without steroids or erythropoietin) have stable or increasing nerve conduction velocities and well controlled blood pressure. If a patient develops such symptoms as insomnia, weakness, dysgeusia, or anorexia, for no apparent reason, inadequate dialysis is suspected. A falling hematocrit, deteriorating nerve conduction velocity, and rising serum creatinine in such a patient are considered as strongly supporting a diagnosis of inadequate dialysis if other causes can be ruled out. If a trial increase in dialysis efficiency (high volume, high frequency or other) abates the signs and symptoms, the diagnosis of inadequate dialysis is considered as very likely and a permanent change of dialysis regimen is recommended.

Inadequate ultrafiltration

Inadequate ultrafiltration on CAPD is defined as failure to generate at least 5.5 ml ultrafiltration per 1 9 of absorbed glucose or 1500 ml of ultrafiltration with glucose infusions of 270-280 glday (e.g. with 2 L infusion volume and 2 exchanges of 2.5% solution + 2 exchanges of 4.25% solution; or with 3 L volumes and 2 exchanges of 2.5% solution + 1 exchange of4.25%).

Peritoneal equilibration test

Peritoneal membrane transport characteristics were evaluated shortly after catheter break-in for all patients starting dialysis since 1983 .For this purpose two liters of 2.5% DianealR are infused into the peritoneal cavity and serial dialysate samples are taken for urea, creatinine, glucose, sodium, potassium, and protein. Blood samples are taken prior to and after the test exchange for analysis of the same solutes. The test is standardized for length of preceding exchange, times of inflow and drainage, patient position, method of sampling, sample handling, and laboratory assays. The residual volumes of pre and postequilibration exchanges are calculated on the basis of dilutional effects of infused dialysis solution. A detailed methodology of the equilibration test is reported elsewhere (6).

Tables I to ill show the results of 103 equilibration tests. Table I presents the number of measurements , minimal values, means -1 standard deviation, means, means + I standard deviation, maximal values, and standard deviations of dialysate to plasma ratios (DIP) at all dwell times for urea, creatinine, protein, corrected creatinine (creatinine corrected for glucose interference), potassium, and sodium.

Table II shows the ratios for dialysate glucose concentration at particular dwell times to dialysate glucose at 0 dwell time (DIDO); the values are presented in similar format to those of DIP .

Table III portrays the results of drain volumes and residual volumes as calculated by glucose, potassium, urea, creatinine, and protein, as well as the mean residual volumes calculated by all 5 solutes. The means were calculated only when calculations of residual volumes in a particular test were available for all 5 solutes, therefore, the number of observations for the means are the lowest.

For each solute the transport rate is categorized as low, low average, high average, and high (Figures I and 2). A low transport rate is defined as a DIP ratio < mean -ISD or a DIDO > mean + ISD. Low average transport is defined as a DIP between the mean -lSD and the mean, or a DIDO between the mean and the mean + lSD. High average transport is a DIP between the mean and the mean + lSD or a DIDO between the mean -lSD and the mean. A high transport rate is present if DIP is > the mean + lSD or DIDO is lower than the mean lSD. The curve of an individual test is categorized according to the position of at least 2 points at 2, 3, and 4 hr dwell time.

Drain volumes and residual volumes are categorized using the same principle as for dialysate to plasma ratios (Figure 2).

Table IV shows a correlation matrix of selected measurements. Excluding creatinine vs corrected creatinine the best correlations were for DIP ratios for corrected creatinine vs sodium corrected creatinine vs glucose, and creatinine vs glucose. The best correlations with drain volume were inverse correlations with DIP sodium and creatinine and positive correlation with DIDO glucose. Creatinine (and corrected creatinine) dialysate to plasma ratios show the best correlations with the clinical responses of the patients to peritoneal dialysis therapy and are most useful for prognostic and diagnostic purposes.

Table V summarizes the prognostic usefulness of the baseline peritoneal equilibration test. The patients with high peritoneal transport rates have poor ultrafiltration on standard CAPD, sometimes even with mostly hypertonic dialysis solutions.

These patients, even after losing residual renal function have adequate dialysis and ultrafiltration with less than 24 hours of dialysis per day; such as NIPD or daytime ambulatory peritoneal dialysis (DAPD).

The best candidates for standard flow CAPD (total dialysis solution infusion volume below 9 L) are patients with high average peritoneal transport rates. They can achieve adequate dialysis even after losing residual renal function and obtain adequate ultrafiltration with moderate dialysis solution glucose concentrations.

Most patients with low average peritoneal transport can be maintained on the standard flow CAPD; however, many of them may require a modified regimen (total dialysis solution inflow 10 mL or morel day, combination of high flow CCPD) when residual renal function becomes negligible, particularly if they have high body surface area. These patients have excellent ultrafiltration with moderate dialysis solution glucose concentrations.

Finally, patients with low peritoneal transport rates usually have excellent ultrafiltration with low dialysis solution glucose concentration and are very likely to develop symptoms of inadequate dialysis.

Table VI portrays the diagnostic value of repeated tests in selected dialysis related problems. The table does not include all possible combinations of peritoneal solute transport, drain volume, and residual volumes, rather the most typical combinations are presented.

Inadequate dialysis in patients with peritoneal solute transport above low average indicates noncompliance to a prescribed dialysis regimen. Inadequate dialysis in patients with less than high average peritoneal solute transport frequently occurs after a loss of residual renal function.

Insufficient ultrafiltration in a patient with stable, high peritoneal solute transport and stable, low drain volume without change in residual volume indicates a loss of residual renal function and a necessity of change to NIPD or DAPD. The diagnosis must be confirmed by a 24-hour urine collection. A reported insufficient ultrafiltration in a patient with stable but less than high peritoneal solute transport and more than low drain volume indicates dietary indiscretions. Dietary counseling rather than change in dialysis prescription is needed.

A gradual decrease in ultrafiltration may indicate excessive lymphatic absorption, mesothelial alterations, or massive peritoneal adhesions (sclerosing peritonitis) depending on a peritoneal solute transport pattem. A unique combination of slow glucose absorption, slow urea equilibration, and sodium concentration in dialysate equal to that in infused dialysis solution has been reported by Verger et at (7) in sclerosing peritonitis.

A sudden drop in ultrafiltration with a corresponding decrease in drain volume but without a change in peritoneal solute transport indicates either a dialysate leak if residual volume is average or low or a catheter malfunction if residual volume is high.

Current peritoneal dialysis modalities at the University of Missouri

Standard CAPD is the most prevalent modality in our institution. More than 55% of patients are on standard flow (7.5-9.0 L dialysis solution inflow per 24 hrs) CAPD, but less than 40% are on standard flow CAPD with 2 L exchanges. Table VII shows the variety of peritoneal dialysis modalities used in our patients at the time of this writing. High flow modalities are used in patients with low average or low peritoneal transport rates. Low flow modalities are used in patients with well preserved residual renal function, standard flow DAPD in patients with high peritoneal transport rates. Table VIII shows treatment time, dialysis solution inflow, and dialysis solution sodium concentration prescribed for 8 patients treated with NIPD as well as reasons of using this modality and patients' peritoneal transport rate. Lower dialysis sodium concentration is required for some patients to achieved appropriate negative sodium balance and blood pressure control.

Most of the patients who are not treated with standard CAPD would have transferred from peritoneal dialysis treatment if modified modalities were not implemented.


  1. Report of the National CAPD Registry of the National Institutes of Health, Released January 1986 covering January 1, 1981 through August 31, 1985. Published by the University of Missouri, Columbia, MO.
  2. Twardowski ZJ, Prowant BF, Nolph KD, Matinez AJ, Lampton LM. High volume, low frequency continuous ambulatory peritoneal dialysis. Kidney Int. , 1983; 23: 64 70.
  3. Twardowski ZJ, Khanna R, Nolph KD, Scalamogna A, Metzler MH, Schneider TW, Prowant BF, Ryan LP. Intra abdominal pressure during natural activities in patients treated with continuous ambulatory peritoneal dialysis. Nephron, 1986; 44: 129-35.
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  7. Verger C, Larpent L, Dumontet M. Prognostic values of peritoneal equilibration curves in CAPD patients. In: Frontiers in Peritoneal Dialysis. Edited by Maher JF and Winchester JF. Published by Field, Rich and Assoc. , Inc. , New York, NY , 1986: 88-93.