Prescribing peritoneal dialysis

INTRODUCTION — 

Peritoneal dialysis is an effective therapy for end-stage kidney disease (ESKD). Modalities include continuous ambulatory peritoneal dialysis (CAPD) and automated peritoneal dialysis (APD). This topic reviews the peritoneal dialysis prescription, including the optimal amount of delivered dialysis, for both modalities. The evaluations of decreased solute clearance and ultrafiltration insufficiency are discussed in detail elsewhere:

●(See "Inadequate solute clearance in peritoneal dialysis".)

●(See "Management of hypervolemia in patients on peritoneal dialysis".)

●(See "Peritoneal equilibration test".)

GENERAL PRINCIPLES

Targeted versus untargeted dialysis — The amount of delivered dialysis should be sufficient to control uremic symptoms and maintain optimal mineral metabolism, electrolyte values, and fluid balance. In general, there are two different dialytic strategies to achieve these aims: an approach that targets a minimum amount of total small-solute removal, as assessed by the Kt/Vurea, and an approach without such targets. Some consensus guidelines [1-4] and many UpToDate contributors endorse the targeted approach, which is used by the United States Centers for Medicare and Medicaid Services as a metric of dialysis adequacy. However, many countries do not utilize a specific target value for Kt/Vurea, a practice supported by some US experts [5] and some UpToDate contributors.

These two different approaches are discussed below:

●Dialysis targeted to Kt/Vurea – For patients in whom a specific amount of small-solute removal is targeted, a sufficient amount of dialysis is prescribed to obtain a total (peritoneal plus residual kidney) Kt/Vurea of 1.8/week so that a minimum total Kt/Vurea of ≥1.7 per week is consistently achieved [1]. For patients on automated peritoneal dialysis (APD), a long dwell is typically prescribed during the day (either all day or at least part of the day) in addition to the nightly exchanges; the clearance of middle-molecular-weight solutes may be decreased in the absence of a long daytime dwell. However, some clinicians do not prescribe a daytime dwell for patients on APD who have significant residual kidney function, especially if a dry period is needed for exercise.

Patient-reported outcomes of well-being, fluid status, and nutrition status are also considered when evaluating the optimal amount of dialysis. If a patient is not doing well in these components despite meeting target Kt/Vurea, the peritoneal dialysis dose should be increased [6]. Other measures of solute clearance, such as creatinine clearance normalized to body surface area, also may be helpful in cases where the urea clearance appears adequate but uremic symptoms or laboratory abnormalities (eg, hyperphosphatemia) persist. (See "Measurement of solute clearance in continuous peritoneal dialysis: Kt/V and creatinine clearance".)

Studies of continuous ambulatory peritoneal dialysis (CAPD) patients have suggested that a weekly Kt/Vurea <1.7 is associated with increasing uremic symptoms, poor nutrition, and anemia [7-11]. The best data are from a randomized study from Hong Kong in which 320 new CAPD patients were assigned to a target Kt/Vurea of 1.5 to 1.7, 1.7 to 2, or >2 [10]. All patients had residual kidney urea clearance <1, and the clearance provided by residual kidney function was added to the peritoneal clearance. There were no differences among groups in survival, serum albumin levels, and hospitalization rates. However, more patients assigned to a dialysis dose of <1.7 were switched from peritoneal dialysis to hemodialysis by their clinician compared with those in the other two groups (16 versus 7 and 6, respectively). Reasons for withdrawing from peritoneal dialysis included inadequate ultrafiltration (n = 13), uremic symptoms (n = 6), and excessive ultrafiltration (n = 10). Patients assigned to the lower dialysis dose also required higher doses of erythropoietin than those in the other two groups, although hemoglobin concentrations were not different between groups.

For most patients, targeting a Kt/Vurea significantly higher than 1.7 does not appear to provide additional clinical benefit. This was suggested by two prospective, randomized, controlled clinical trials [10,12] and in multiple observational studies [13-16]. However, if the achieved Kt/Vurea is above the minimum threshold and the patient has uremic symptoms, it is reasonable to try a higher dose of dialysis.

There are no studies that have compared different Kt/Vurea targets among APD patients, and it is not known whether the benefits conferred by a minimum Kt/Vurea ≥1.7 in CAPD are also observed in APD. It is possible that the clearance of middle-molecular-weight solutes is lower in APD than in CAPD, if a daytime dwell is not used, even if the minimum Kt/V ≥1.7 is achieved [17]. The clearance of middle-molecular-weight solutes may require a longer dwell time. APD differs from CAPD in that CAPD patients typically undergo dialysis 24 hours per day; whereas, in the absence of a daytime dwell, APD provides dialysis only over eight to nine hours at night. APD dwells (at least at night) are shorter and not as saturated with solutes as the typical daytime dwell for CAPD, in part because there is less time for diffusion.

●Dialysis not targeted to Kt/Vurea – The alternative approach to prescribing peritoneal dialysis focuses on patient preferences and clinical symptoms without targeting minimum values of small solute removal. This practice, which is endorsed by some UpToDate contributors, works best when patients have a significant amount of residual kidney function. In this schema, the importance of small solute kinetics is deemphasized; rather, a dialysis dose is considered adequate provided symptom burden, mineral metabolism, electrolyte values, and fluid balance are optimized.

This approach is called incremental peritoneal dialysis. For a patient with substantial residual kidney function who is initiating dialysis, a typical incremental peritoneal dialysis prescription consists of a relatively small number of low-volume, low-dextrose exchanges (eg, two to three 1500 mL exchanges using 1.5 percent dextrose or combinations of 1.5 percent/2.5 percent dextrose). Because the incremental dialysis regimen may require intensification over time, especially if residual kidney function diminishes, patients must be followed closely to identify early symptoms of uremia or signs of volume overload.

Although incremental peritoneal dialysis is associated with an increased risk of volume overload compared with conventional peritoneal dialysis, it can have a major positive impact on quality of life. Other potential benefits may include reduced peritonitis risk, preservation of residual kidney function, preservation of the peritoneal membrane, and reduced systemic complications of glucose exposure [18].

Kt/Vurea — In peritoneal dialysis, urea removal is a marker for small-solute removal. Studies have used Kt/Vurea, which is the product of urea clearance (K) and time (t) normalized to total body water (V), as a metric of urea removal to quantify the amount of delivered dialysis. A minimum total (peritoneal plus residual kidney) Kt/Vurea that is associated with better outcomes has been identified. (See 'Targeted versus untargeted dialysis' above.)

A major determinant of peritoneal urea clearance is the total drain volume (dialysate plus ultrafiltration volume) (see 'Calculation of peritoneal Kt/V urea' below). Drain volume is dependent upon ultrafiltration, infused volume, duration of individual dwells, and frequency of exchanges. These variables are the basic components of the dialysis prescription. (See 'Initial prescription' below.)

Calculation of peritoneal Kt/V urea — The peritoneal Kt/Vurea is calculated from the daily peritoneal urea clearance (Kt) and the volume of distribution of urea (V). Instructions to calculate peritoneal Kt/Vurea and an illustrative example are provided below:

●Calculating peritoneal Kt/Vurea – The daily peritoneal urea clearance (Kt) is the product of the total 24-hour peritoneal drain volume and the ratio of the urea concentration in the pooled drained dialysate to that in the plasma (D/P urea). A 24-hour collection of dialysate is used rather than shorter collections because it provides more accurate estimates of clearance compared with values obtained from shorter collections or from kinetic modelling programs [19].

The volume of distribution of urea (Vurea) is approximately equal to body water (ie, 60 percent of ideal body weight in kg in men and 55 percent of ideal body weight in kg in women).

We do not use the actual weight to estimate the volume of distribution for urea; rather, we use the ideal body weight or, for patients with obesity, the adjusted body weight (calculator 1) [1]. Using the actual body weight often results in under- or overestimating the Kt/Vurea [20,21]:

•Very large patients usually have increased adiposity, which increases weight and hence the “V” in the unadjusted Kt/V. However, adipose tissue is not part of the true volume of distribution of urea. Therefore, large patients may have a low Kt/Vurea suggesting under-dialysis but have no clinical evidence of under-dialysis.

•Conversely, severely malnourished individuals may have an adequate Kt/Vurea but have uremic symptoms or other signs of under-dialysis. Overestimating the Kt/Vurea in patients who are losing weight and/or malnourished is especially problematic because inadequate dialysis is often a cause of anorexia and malnutrition.

●Collecting drain volume – To collect a drain volume on APD, patients take a large drain bag home and connect it to the drain line from the cycler. For 24 hours, all the dialysate is collected from the initial drain and nighttime exchanges. If a patient performs a midday exchange on APD, he or she must remember to collect that dialysate as well.

To collect a drain volume on CAPD, patients gather all the individual drain bags from their manual exchanges over a 24-hour period.

The volume of drained dialysate is carefully recorded from the cycler data and/or by pouring manual drain bags into a measuring container. A small sample (1/1000^th of the volume from each bag of dialysate) is collected using the “aliquot” method [22] and then sent for measurements of urea concentration. The “aliquot” collection method is typically performed by the home dialysis center, but may be performed by patients at home to avoid transporting heavy dialysate drain bags.

●Illustrative example – An example of Kt/Vurea calculation for a representative patient is provided here.

A 70 kg man on CAPD has a total 24-hour peritoneal drain volume of 10.5 L.

Laboratory studies:

•Pooled dialysate urea – 38 mg/dL

•Plasma urea – 40 mg/dL

Addition of residual kidney function — Residual kidney function provides an important contribution to total small solute removal for many patients on peritoneal dialysis.

●Urine Kt/Vurea – If the patient has significant residual kidney function, the solute removal provided by the kidney (as assessed by urine Kt/Vurea) should be added to the Kt/Vurea provided by peritoneal dialysis for an assessment of total solute removal. Significant kidney function is defined by National Kidney Foundation (NKF)-Kidney Disease Outcomes Quality Initiative (KDOQI) as a urine volume >100 mL/day [1].

We are able to reduce the dialysis dose in patients with residual kidney function because less dialysis is required to meet the target total solute removal. Some clinicians ignore the contribution of residual kidney function to total solute removal and prescribe the total minimum recommended dialysis dose. As a result, the patient ends up performing more dialysis than is required, which makes the dialysis prescription more demanding and time consuming for the patient than necessary. If residual kidney function declines, the clearance provided by peritoneal dialysis must be increased in order to meet the target total Kt/Vurea and to manage symptoms. The total solute removal (from peritoneal dialysis and residual kidney function) should be monitored. (See 'Adjustment in prescription' below.)

A lower dose of dialysis may be sufficient for many months. One study found that a weekly Kt/Vurea of 2 could be maintained for approximately 1.5 years by using only one or two nightly exchanges among APD patients with significant residual function [23]. Such dosing methods allow patients with significant residual kidney function to begin dialysis with less intensive, more manageable regimens [24].

●Calculating and incorporating urine Kt/Vurea – Residual kidney function is estimated by determining the urea clearance from a 24-hour urine collection and from the plasma urea. The 24-hour urine collection is routinely performed by the patient at the same time that the 24-hour peritoneal dialysate is collected for calculation of the peritoneal dialysis Kt/V. The calculation of residual kidney function is described here:

The 70 kg man on CAPD in the illustrative example above (see 'Calculation of peritoneal Kt/V urea' above) has a urine output of 500 mL per day.

Laboratory studies:

•Urine urea – 230 mg/dL

•Plasma urea – 40 mg/dL

This number is added to the Kt/Vurea provided by peritoneal dialysis for the total achieved weekly Kt/Vurea:

In this example, the patient's residual kidney function provides a substantial contribution to the total weekly removal of solute. If this patient loses residual kidney function, failure to adjust the prescription for the loss of residual kidney function by increasing the dialysis dose could lead to under-dialysis, even though there has been no decline in the peritoneal dialysis efficiency (figure 1) [9,25,26].

Translating Kt/Vurea to total volume of exchanges — To formulate the initial dialysis prescription using a small-solute targeted approach (see 'Targeted versus untargeted dialysis' above and 'Initial prescription' below), we estimate the minimal total amount of infused dialysate required to obtain the desired weekly Kt/Vurea (ie, 1.8/week).

For example, in a 70 kg anuric man:

●V  =  70 kg  x  0.6  =  42 L

●Target weekly Kt/Vurea 1.8  ÷  7 days is approximately 0.26 per day

●Daily Kt/Vurea  =  0.26

●Daily Kt/42 L  =  0.26

●Daily Kt  =  11 L (estimated required urea clearance per day)

When using this equation to estimate the initial prescription, we assume that urea is being fully equilibrated in the peritoneal dialysate (D/P urea = 1). As a result, the volume of drained dialysate volume is effectively equal to the urea clearance, as shown here:

●Urea clearance  =  D/P urea  x  Volume

●Volume  =  Urea clearance  ÷  (D/P urea)

●Volume  =  11 L  ÷  1  =  11 L (assuming D/P urea is 1)

Thus, for a 70 kg man to achieve a weekly Kt/Vurea of 1.8 with peritoneal dialysis clearance only, he will need 11 L of drained dialysate volume per day.

For the initial prescription, we accept two assumptions:

●There is complete equilibration between plasma urea and dialysate. Since clearance is equal to D/P urea x volume, complete equilibration results in the maximum achievable D/P urea of 1 (and thus an effective clearance of 11 L). However, these levels of equilibration are not observed in practice. This means that the dialysis prescription may need to be revised when the Kt/Vurea is measured based on the actual dialysis that is performed by the patient. We calculate a Kt/Vurea based on a 24-hour drain volume collection approximately two weeks after starting therapy.

●The patient will have at least 1 L of ultrafiltration per day that is also fully equilibrated with urea. We subtract the additional volume achieved with ultrafiltration from the 11 L prescription.

As a result, 11 L of total target clearance minus 1 L of expected ultrafiltration clearance = 10 L dialysate dwell volume clearance.

Therefore, we prescribe a regimen that uses at least 10 L of infused dialysis volume.

If the patient has significant residual kidney function (ie, urine volume >100 mL/day), the starting volume of peritoneal dialysis can be reduced by calculating the daily residual urea clearance.

For example, in a 70 kg man with residual kidney function:

●24-hour urine volume  =  1 L

●24-hour urine urea  =  200 mg/dL

●Plasma blood urea nitrogen (BUN)  =  45 mg/dL

The new target Kt/Vurea could then be modified:

The prescription for this example should provide approximately 7 L of drained dialysate (rounded up from 6.3 L). In practice, for APD, the prescribed infused dialysate volume is also defined by logistics since dialysate is only provided by the manufacturer in 2, 3, 5, and 6 L bags for APD. In this example, the infused volume could be 6 L (ie, using one 5 L bag and one 2 L bag to allow some extra) to provide 7 L drained dialysate (infused volume 6 L plus ultrafiltration 1 L).

PERITONEAL DIALYSIS MODALITY — 

We help patients choose the dialysis modality (automated peritoneal dialysis [APD] or continuous ambulatory peritoneal dialysis [CAPD]) that best fits their lifestyle. Although the modality historically was selected to match specific peritoneal membrane transport characteristics, both APD and CAPD can be modified to meet the needs of most patients. (See "Evaluating patients for chronic peritoneal dialysis and selection of modality".)

INITIAL PRESCRIPTION — 

In peritoneal dialysis, sterile peritoneal dialysis solution is infused into the peritoneal cavity through a flexible permanent catheter. After dwelling for a specific period of time ("dwell"), the fluid is drained and fresh fluid instilled ("exchange"). Exchanges are performed manually by the patient in continuous ambulatory peritoneal dialysis (CAPD) and by a cycler (usually used overnight) in automated peritoneal dialysis (APD) [27].

The components of the peritoneal dialysis prescription are discussed here.

Daily dialysate volume — The initial prescription is based on the total volume of infused dialysate that is required (see 'Translating Kt/Vurea to total volume of exchanges' above). The delivery strategy is different for CAPD and APD.

Continuous ambulatory peritoneal dialysis — CAPD involves multiple exchanges (usually three to four) during the day, followed by a single overnight dwell. Variables that must be considered include:

●The total number of exchanges per day – Lifestyle and work schedule must be taken into account. Each exchange takes 15 to 30 minutes, depending on catheter performance, and requires access to supplies, which are generally kept at home. As a result, the patient usually returns home to perform exchanges, which may interfere with work. A patient who works at home may be able to perform more exchanges during the day.

●The volume used in each exchange (ie, fill volume) – Patients can usually tolerate between 1.25 to 1.5 L/m² body surface area [24,28], which usually translates into 2 to 2.5 L fill volumes. Different volumes may be instilled at different times. For example, a larger fill volume can be used during the long night dwell when the patient is supine and has lower intra-abdominal pressures. Similarly, at the start of peritoneal dialysis, some patients may feel bloated with conventional dwell volumes and may start with smaller volumes as adequacy considerations allow.

The total volume to be infused per day is determined from the Kt/V as described above (see 'Translating Kt/Vurea to total volume of exchanges' above). To minimize the burden of dialysis, we measure the residual kidney function and incorporate it into the calculations. (See 'Addition of residual kidney function' above.)

For the 70 kg anuric male patient who needs 10 L of infused peritoneal dialysis solution per day, we could start with the following prescription:

●Three exchanges of 2.4 L (at breakfast, lunch, and dinner) and a bedtime exchange of 2.5 L

And, for the 70 kg male patient with residual kidney function above who needs only 6.3 L of peritoneal infused dialysis solution per day, we could start with the following prescription:

●Three exchanges of 2.1 L per day (at breakfast, midday, and bedtime)

Dialysate for CAPD is provided in 2, 2.5, and 3 L bags. In order to infuse 2.1 L, the 2.5 L dialysate bag is suspended from a hanging scale and allowed to infuse by gravity. The full bag weighs 2500 g prior to infusion. The patient stops the infusion when the bag weighs 400 g, indicating 400 mL of dialysate remains in the bag and 2100 mL has been infused.

Automated peritoneal dialysis — APD is more complex than CAPD. We address the following variables:

●The length of time that the patient may be connected to the cycler – We try to prescribe a cycler time of no more than nine hours. Most patients sleep for fewer than eight hours per night, so prescribing a cycler time longer than eight hours means that the patient will have to stay connected to the cycler for some time either prior to sleeping or after awakening. It is important to involve the patient in this discussion from the outset so they know what to expect.

●The number of overnight exchanges – We usually prescribe three to five exchanges per night. A greater number of exchanges limits the dwell time per exchange since a significant amount of time is spent draining and filling the patient. Short dwell times reduce solute removal, particularly sodium and middle molecules [24].

●Addition of a long dwell during the day – We start most patients with a daytime dwell in order to add time-dependent clearance. As discussed above, Kt/Vurea recommendations for APD patients are based upon studies of CAPD patients, who undergo dialysis 24 hours per day. Even if minimum Kt/V thresholds are met, the clearance of middle-molecular-weight solutes may be reduced if the prescription does not also provide close to 24 hours of dialysis daily. (See 'Targeted versus untargeted dialysis' above.)

The daytime dwell may be a full-day dwell (ie, 15 hours) or partial-day dwell (four to eight hours). The dialysate composition needs to be adjusted if a full-day dwell is used in order to prevent the absorption of dialysate, which could cause volume overload. (See 'Ultrafiltration' below.)

●The volume used in each exchange (ie, fill volume) – We generally start with volumes of 1.8 to 2.2 L for exchanges at night. In smaller patients, or those who feel bloated, even smaller volumes can be used to start. We do not use fill volumes greater than 3 L.

We start patients with a smaller volume during the day (ie, 0.6 to 1.2 L). Patients may not tolerate the same volumes when they are upright as they do when supine (at night on the cycler) because of higher intraperitoneal pressures when upright [28].

So, for the 70 kg anuric male patient described above (see 'Translating Kt/Vurea to total volume of exchanges' above) who needs 10 L of peritoneal dialysis per day, we could start with the following prescription:

●Nine hours  x  four exchanges  x  2200 mL overnight with a partial day dwell of 1200 mL

For the 70 kg male patient with residual kidney function who needs approximately 6.3 L (see 'Translating Kt/Vurea to total volume of exchanges' above), we round off to 7 L and start with the following prescription:

●Eight hours  x  three exchanges  x  2000 mL overnight with a partial day dwell of 1000 mL

For some patients with significant residual kidney function, some clinicians prescribe three to four exchanges over nine hours for four to six nights per week, without a daytime dwell. Some patients may prefer not to perform manual exchanges during the day. If patients are undergoing dialysis only four to six nights per week, the calculated achieved standardized Kt/Vurea must be adjusted accordingly.

If the example above is used, the measured Kt/Vurea must be multiplied by 4, 5, or 6, rather than 7, to determine the standardized Kt/Vurea, depending on the number of nights that the patient performs dialysis.

Thus, for the example used above in which the measured daily peritoneal Kt/Vurea is approximately 0.24, the weekly Kt/Vurea of a patient performing dialysis four nights per week is 0.24 x 4 = 0.96.

These types of prescriptions can only be used in patients with significant residual kidney function as a gradual start to peritoneal dialysis.

Ultrafiltration

Target weight and ultrafiltration goal — The aim of ultrafiltration is to maintain euvolemia and prevent fluid overload. Fluid overload has been associated with increased mortality among peritoneal dialysis patients [15,29-37]. To achieve this aim, we set a tentative target weight and an initial ultrafiltration goal.

●Target weight – We set a tentative target weight at the beginning of peritoneal dialysis training. The target weight is the weight at which the patient is believed to be euvolemic or as close to euvolemic as possible. If the patient has clinical evidence of volume overload at the time of this assessment, then we set the target weight several kilograms below the starting weight. The target weight is then reassessed at every visit.

We ascertain the target weight based upon our clinical assessment (blood pressure, edema, symptoms of fluid overload, and comorbidities). Provided the patient is weighed in a consistent manner, the target weight may be established with either a “dry” abdomen or with a dialysate dwell. Bioimpedance analysis may be useful, in addition to clinical assessment, for determination of the target weight [38], although its benefit has not been consistently demonstrated [39,40].

●Ultrafiltration goal – If the patient still makes urine, we use diuretics to help maintain the urine volume [41]. Many patients starting peritoneal dialysis have sufficient urine volume such that ultrafiltration is not necessary. If the patient is anuric, we aim for 1 L fluid removal per day to balance the oral intake of fluid, assuming the patient's daily fluid intake is no more than 1 L. We do not target an ultrafiltration volume beyond that which is necessary to balance fluid intake. Aiming for a negative fluid balance may result in excessive ultrafiltration, which could impair residual kidney function. Instead, the goal is to maintain residual kidney function as long as possible, which has been associated with better survival (See "Residual kidney function in kidney failure", section on 'Survival'.)

The patient is instructed to check weight and assess for evidence of fluid overload (edema, hypertension, orthopnea) daily. If the weight increases above the target weight, or the patient has edema, hypertension, or orthopnea, then the patient is advised to increase the ultrafiltration goal. Ultrafiltration per day should be decreased if the weight is lower than the target weight or if the patient's blood pressure is low.

Ultrafiltration strategy — The amount of ultrafiltration is modulated by varying the dextrose concentration of the dialysate solution. The standard dextrose concentrations are 1.5, 2.5, and 4.25 percent. We instruct both APD and CAPD patients to use higher percentage dextrose solutions if they need to increase ultrafiltration. Icodextrin may be used as an alternative to dextrose during long dwells. Icodextrin is a high-molecular-weight glucose polymer that is absorbed more slowly than dextrose and is more effective for sustained ultrafiltration over long periods of time.

Continuous ambulatory peritoneal dialysis — For daytime dwells in CAPD patients, we start with either 1.5 or 2.5 percent dextrose. Generally, some combination of these concentrations will yield ultrafiltration of approximately 1 liter per day.

For the nighttime dwell, we use a 2.5 percent dextrose solution or an icodextrin dwell. The nighttime dwell in CAPD is a long dwell, and a higher concentration of solute is required to limit the possibility of net fluid absorption. However, some patients may be able to use a 1.5 percent solution overnight without fluid reabsorption, depending upon membrane characteristics.

Automated peritoneal dialysis — The initial prescription varies depending on the volume status of the patient and the presence of residual kidney function.

●If the patient is clinically euvolemic and anuric (such as the patient described in the example above), we initiate dialysis with 2.5 percent dextrose solution for all nighttime dwells. Generally, this allows approximately 1 L of ultrafiltration per night.

The prescription is revised based on weights and blood pressure. We suggest that patients try different strength dextrose solutions and combinations at night, while closely monitoring the resulting ultrafiltration, so that they learn which combinations work for a given situation. For example, on the cycler, patients may use a 6 L bag of 1.5 percent dextrose solution and a second 6 L bag of 2.5 percent dextrose solution. The resulting ultrafiltration varies between patients depending on individual membrane transport characteristics.

●In a patient with significant residual kidney function, we initiate dialysis with 1.5 percent dextrose for nighttime dwells because that patient can rely on urine output to help control volume.

●For the daytime dwell, we prescribe 2.5 percent dextrose solutions or icodextrin. If dextrose is used, we limit the dwell to a partial day (manual drain after four to eight hours). If icodextrin is used, a full-day dwell may be used. A higher dextrose or icodextrin solution during the daytime dwell may limit the absorption of fluid into the body. However, even if the higher dextrose or icodextrin is used, it is important to monitor the initial drain volumes during a full-day dwell to make sure net fluid absorption into the body is not occurring. (See 'Follow-up visits' below.)

Dialysate composition — The composition of dextrose-based peritoneal dialysate solutions available in the United States includes sodium (132 mEq/L), magnesium (0.5 mEq/L), chloride (95 mEq/L), and lactate for a bicarbonate source (40 mEq/L). There is no potassium in the solutions. There are different concentrations of calcium available (2.5 and 3.5 mEq/L). We typically start patients on the 2.5 mEq/L calcium solutions and increase to the higher calcium concentration only if there is persistent hypocalcemia with medical treatment of bone mineral metabolism. The dextrose concentrations are 1.5, 2.5, and 4.25 percent.

Icodextrin dialysate contains 7.5 percent icodextrin and sodium (132 mEq/L), magnesium (0.5 mEq/L), chloride (96 mEq/L), lactate (40 mEq/L), and calcium (3.5 mEq/L).

In general, we discourage routine use of additives to peritoneal dialysis solutions in order to reduce the risk of contamination.

We occasionally use heparin (dosed at 500 or 1000 units/L) if there is visible fibrin in the drain bag that seems to accompany slow fill or drain times. Often, we are able to achieve improved results by dosing heparin only two or three times per week. (See "Microbiology and therapy of peritonitis in peritoneal dialysis", section on 'Dialysis prescription'.)

We do not add potassium to dialysate. Patients may require oral potassium supplementation or administration of mineralocorticoid antagonists to prevent hypokalemia.

FOLLOW-UP VISITS

Frequency of visits — Patients should be evaluated within two weeks after they start performing peritoneal dialysis at home and, until stable, at least every month thereafter. In our unit, the patient is routinely followed in the home training unit twice a month; once to see the home training nurse and once to see the nephrologist and the full multidisciplinary team. However, many units only see the patient monthly. In other units, stable patients are seen every two to three months. Patients are also evaluated any time they have an acute clinical problem related to dialysis. (See "Inadequate solute clearance in peritoneal dialysis", section on 'Routine monitoring for adequate clearance'.)

Assessment of uremic symptoms, mineral metabolism, and electrolytes — We assess weights, blood pressures, and ultrafiltration volumes achieved with each exchange. We assess volume status and uremic symptoms and check monthly laboratory values, including blood urea nitrogen (BUN), creatinine and electrolytes, and measures of mineral metabolism. (See "Inadequate solute clearance in peritoneal dialysis", section on 'Routine monitoring for adequate clearance' and "Management of hypervolemia in patients on peritoneal dialysis", section on 'Monitoring'.)

The dialysis prescription may be adjusted based upon the assessment. However, when starting peritoneal dialysis, it is usually prudent to give the patient four to eight weeks on a prescription before making any changes provided the total weekly Kt/Vurea is ≥1.7; dialysis takes time to improve uremic parameters.

Indications to increase the amount of dialysis are defined elsewhere. (See "Inadequate solute clearance in peritoneal dialysis".)

Fluid balance — We routinely re-evaluate target weight based on clinical exam, dietary history, and by any changes in cardiovascular status. If a patient develops pedal and pulmonary edema, orthopnea, or unexplained higher blood pressure at the prescribed target weight, he or she has likely lost body mass, and the target weight needs to be set lower to better approximate euvolemia. (See "Management of hypervolemia in patients on peritoneal dialysis".)

Monitoring of Kt/Vurea and residual kidney function — For patients in whom a specific amount of small-solute removal is targeted (see 'Targeted versus untargeted dialysis' above), we measure the achieved Kt/Vurea one to two weeks after the patient starts performing dialysis at home and every three to four months thereafter. While the delivery strategies defined above will provide adequate solute removal for most patients, measuring the delivered dialysis dose can be informative. In individual patients, dwell times and transport type affect the drain volume per exchange. As an example, the dextrose may be quickly absorbed with a standard dwell time in a patient who rapidly transports solute. Once the osmotic gradient is neutralized, fluid will be absorbed from the peritoneal cavity if the dwell continues. Not only would there be no ultrafiltration from that exchange, but the drain volume could be less than the instilled volume. Lower drain volumes may result in less solute removal and fluid overload.

Kt/Vurea is checked anytime the prescription is changed.

We measure residual kidney function at least every other month; some clinicians measure this monthly if total Kt/Vurea is close to the target Kt/Vurea minimum. (See "Inadequate solute clearance in peritoneal dialysis", section on 'Routine monitoring for adequate clearance'.)

ADJUSTMENT IN PRESCRIPTION — 

The dialysis dose should be increased if there are persistent uremic signs and symptoms. For patients in whom a specific amount of small-solute removal is targeted (see 'Targeted versus untargeted dialysis' above), the dialysis dose also should be increased if the measured weekly total Kt/Vurea is <1.7. The most common reason for a decline in Kt/Vurea is a loss in residual kidney function.

To determine a new prescription, we repeat our back calculation with the current residual kidney function and calculate how much peritoneal clearance is now needed.

For example, our 70 kg man with residual kidney function above who dialyzes with 7 L of peritoneal dialysis per day was found to have a drop in total weekly Kt/Vurea (urine + peritoneal dialysis) to below 1.7. His 24-hour urine volume has dropped from 1 L to 500 mL. We confirmed that this was a complete 24-hour urine collection. He feels well generally except for some increased fatigue and decreased desire for food.

The total (urine + peritoneal dialysis) target daily Kt/Vurea is 0.26 to achieve a weekly Kt/Vurea of 1.8.

Before, the patient had a daily urine Kt/Vurea of 0.11 to contribute to this clearance; it has now dropped to 0.05.

The new target daily Kt/Vurea from peritoneal dialysis needs to be recalculated:

●New target daily Kt/Vurea  =  0.26 – 0.05  =  0.21

●Kt/42 L  =  0.21

●Kt urea  =  8.8 L/day (increased from 6.3 L)

Assuming D/P urea is 1, the amount of drained dialysate volume is:

●Urea clearance  =  D/P urea  x  Volume

●Volume  =  Urea clearance  ÷  (D/P urea)

●Volume  =  8.8  ÷  1  =  8.8 L

With these data, we increase the daily drained dialysate volume from 7 to 9 L (rounded up from 8.8 L). If we assume a daily ultrafiltration volume of 1 L, then our daily infused dialysate volume will increase from 6 to 8 L. In automated peritoneal dialysis (APD), this can be done by evenly distributing the 2 L increase over the cycler dwells and the day dwell. Alternatively (particularly if an increase in fill volume would not be tolerated), an additional cycler exchange or a midday manual exchange could be added to provide the increased volume.

It should be noted that, in APD, not all changes to the prescription volume will yield the same results in solute clearance. Adding a midday exchange may increase solute clearance much more than adding an additional exchange on the cycler, for example. Some programs use modeling software that helps identify changes that will be most effective.

In continuous ambulatory peritoneal dialysis (CAPD), the increase in fill volume could be distributed evenly across all of the exchanges. If an increase in fill volume would not be tolerated well, an additional exchange could be added. Another solution, if amenable to the patient, would be to change from CAPD to APD.

SOCIETY GUIDELINE LINKS — 

Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Dialysis".)

INFORMATION FOR PATIENTS — 

UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5^th to 6^th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

●Basics topic (see "Patient education: Peritoneal dialysis (The Basics)")

●Beyond the Basics topic (see "Patient education: Peritoneal dialysis (Beyond the Basics)")

SUMMARY AND RECOMMENDATIONS

●General principles – The amount of delivered dialysis should control uremic symptoms and maintain optimal mineral metabolism, electrolyte values, and fluid balance. When formulating the peritoneal dialysis regimen, many UpToDate contributors target a minimum amount of total small-solute removal, as assessed by the Kt/Vurea. In the targeted approach, a sufficient amount of dialysis is prescribed to obtain a total (peritoneal plus residual kidney) Kt/Vurea of 1.8/week so that patients may consistently achieve a minimum total Kt/Vurea of ≥1.7 per week. (See 'Targeted versus untargeted dialysis' above and 'Kt/Vurea' above.)

●Peritoneal dialysis modality – We help patients choose the dialysis modality (APD or continuous ambulatory peritoneal dialysis [CAPD]) that best fits their lifestyle. Although the modality historically was selected to match specific peritoneal membrane transport characteristics, both APD and CAPD can be modified to meet the needs of most patients. (See 'Peritoneal dialysis modality' above and "Evaluating patients for chronic peritoneal dialysis and selection of modality".)

●Initial prescription – To formulate the initial dialysis prescription, many UpToDate contributors estimate the minimal daily volume of infused dialysate required to obtain a weekly Kt/Vurea of 1.8/week. If the patient has residual kidney function (defined as urine volume >100 mL/day), the daily dialysate volume is reduced by calculating the daily residual urea clearance. The strategies to deliver the specific amount of daily dialysate are different in APD and CAPD. (See 'Translating Kt/Vurea to total volume of exchanges' above and 'Daily dialysate volume' above.)

●Initial ultrafiltration strategy – To maintain euvolemia and prevent fluid overload, we set a tentative target weight and an initial ultrafiltration goal. Many patients starting peritoneal dialysis have sufficient urine volume such that ultrafiltration is not necessary. The amount of ultrafiltration is modulated by varying the dextrose concentration of the dialysate solution. Our ultrafiltration strategy depends on modality (ie, APD versus CAPD). (See 'Ultrafiltration' above.)

●Subsequent dialysis regimen – After the initial prescription, the subsequent dialysis prescription is modified based on uremic symptoms, control of mineral metabolism, electrolyte values, volume status, and residual kidney function. Many UpToDate contributors also modify the prescription based on measured Kt/Vurea (see 'Follow-up visits' above and 'Adjustment in prescription' above). The evaluations of inadequate solute clearance and ultrafiltration insufficiency are detailed elsewhere. (See "Inadequate solute clearance in peritoneal dialysis" and "Management of hypervolemia in patients on peritoneal dialysis".)

ACKNOWLEDGMENT — 

The UpToDate editorial staff acknowledges William L Henrich, MD, MACP, who contributed to earlier versions of this topic review.