NKF K/DOQI GUIDELINES 2000
 
 

GUIDELINES FOR PERITONEAL DIALYSIS ADEQUACY

II. Measures of Peritoneal Dialysis Dose

GUIDELINE 3

Frequency of Delivered PD Dose and Total Solute Clearance Measurement Within Six Months of Initiation (Opinion)

The total solute clearance (delivered PD dose plus residual kidney function) should be measured at least twice and possibly three times within the first 6 months after initiation of PD. For patients initiating dialysis for the first time and/or patients with substantial residual kidney function, the first measurement should be performed approximately 2 to 4 weeks after initiation of PD. For patients transferring from another renal replacement therapy to PD and/or for patients who do not have substantial residual kidney function, the first measurement of delivered dose of PD should be made by 2 weeks after initiation of PD. To establish a baseline, at least one and possibly two additional measurements will need to be performed in the subsequent 5 months. The frequency of measurement of residual kidney function depends on the PD prescription of incremental versus full dose (see Table II-1).

Rationale Adequate total solute clearance (delivered dose of PD plus residual kidney function) will improve patient outcomes (see Guideline 15: Weekly Dose of CAPD). To assure delivery of adequate solute clearance, measurements for solute clearance are required. In dialysis, as in other human endeavors, continuous education and repetition of a process diminish the frequency of errors, or at least increase the likelihood of recognition of such errors and compensation for them. Furthermore, physiological variations occur which must be taken into account.17 These lines of reasoning apply to measurement of the dose of PD. Thus, measurement of delivered PD dose should be repeated periodically. The recommendation to measure CCr and Kt/Vurea three times within the first 6 months relates to items discussed in Guideline 7: PD Dose Troubleshooting, specifically, establishing a baseline creatinine excretion and following residual kidney function. The rationale for three measurements in the first 6 months is to establish a more accurate baseline excretion of creatinine.

Table II-1. Peritoneal Dialysis Dose and Total Solute Clearance Measurement Schedule: Initial 6 Months
PD Fluid PET Urine*
Month Kpt/Vurea CCr p Krt/Vurea CCr r

1†

X X X X X
2‡       Y Y
3‡       Y Y
4‡ X X   X X
5‡       Y Y
6‡ X X   X X
NOTE. X, measurement; Y, additional measurement if "incremental" PD utilized
* For patients who void infrequently (<3 times in 24 hours), collect urine over a 48-hour period.
† If possible, at the end of month 1, but at the end of training if that is more convenient.
‡ The measurement interval in months 2 to 6 is flexible. At least one additional measurement after the first month’s measurement is necessary. If the results of the second measurement are similar to those of the first measurement, an adequate baseline is established, obviating the third measurement. If the result of the second measurement is discrepant, a third measurement is necessary to establish a more reliable baseline.


Two measurements within the first 6 months are probably sufficient if the results are similar. Based on our collective personal experience, the Work Group believes that patient compliance with a prescribed PD regimen is highest soon after initiation of PD, eg, within the first 6 months; hence, this period is used to establish a baseline.

Delivered peritoneal dialysis dose depends on many factors, including the transport properties of the peritoneal membrane, assessed by the peritoneal equilibration test (PET).18,19 There is evidence that the PET performed within the first week after initiation of PD may yield higher transport results than a PET performed a few weeks later.20 This difference is statistically significant, but may not be clinically relevant. It may be more convenient to perform the first PET at the end of training, rather than at the end of the first month, and the Work Group thinks this is acceptable. However, the results after a month of PD may more accurately reflect peritoneal transport properties for the subsequent period.

In patients initiating ESRD therapy for the first time who have some RKF, delaying the PET and the first measurement of delivered dose for a month is safe and appropriate. However, for patients initiating PD because of transfer from HD and/or for patients who do not have substantial RKF, the first measurement of delivered dose of PD should be performed earlier. In the absence of substantial RKF, waiting 1 month to measure delivered dose may result in inadequate dialysis for 1 month. Thus, the Work Group recommends that these patients undergo measurement of delivered dose of PD at 2 weeks postinitiation, assuming maintenance exchange volumes have been achieved. Patient care technicians may be able to perform these measurements.

If "incremental" PD is initiated instead of "full dose" (see Guideline 1: When to Initiate Dialysis–Kt/Vurea Criterion, and Appendix A, Detailed Rationale for Guideline 1), RKF must be followed carefully and frequently such that PD dose can be increased as RKF deteriorates. While urine production rate is presumed to be a clue to deteriorating RKF, that is not always the case.21 Thus, for patients initiating PD with "incremental" PD, the Work Group recommends measuring RKF every 2 months. For patients on "full dose" PD, the Work Group recommends measuring RKF with total solute removal measurements every 4 months. If urine production rate is decreasing, measure RKF every 2 months or as often as needed and considered helpful, but at least every 4 months. Once weekly Krt/V falls to less than 0.1, RKF can be considered negligible and its routine measurement can be stopped. Guideline 11: Dialysate and Urine Collections, addresses this subject again.

GUIDELINE 4

Measures of PD Dose and Total Solute Clearance (Opinion)

Both total weekly creatinine clearance normalized to 1.73 m2 body surface area (BSA) and total weekly Kt/Vurea should be used to measure delivered PD doses.

Rationale A valid and reproducible measure of PD dose is essential to assess the quantity of dialysis delivered to an individual patient. The quantity of dialysis is an important component of the quality of dialysis. Of the few available measures of PD dose, total weekly Kt/Vurea and total creatinine clearance normalized to 1.73 m2 BSA are the best, because they are most strongly associated with mortality and morbidity (see Guideline 15: Weekly Dose of CAPD). Additionally, when properly performed, these measures are reproducible enough to be useful in routine clinical practice.

The urea-based measure, Kt/Vurea, measures removal of the direct product of protein catabolism. The creatinine clearance (CCr) measures removal of a product of muscle metabolism, which provides insight into lean (ie, fat-free, edema-free) body mass and possibly into compliance (see Guideline 7: PD Dose Troubleshooting). In Guideline 1: When to Initiate Dialysis–Kt/V Criterion, and Guideline 15: Weekly Dose of CAPD, there is a discussion of the comparison of these two different measures. See Guideline 6: Assessing Residual Kidney Function, for a definition of total weekly CCr.

These two recommended measures have both been used to measure delivered dialysis dose. Since each measure provides slightly different information, the Work Group recommends that both measures be used. Both creatinine and urea concentration can be obtained on the same sample of urine, blood, and dialysate. No additional samples need to be collected to perform both, rather than one, of these measures. Most laboratories perform both measures simultaneously (eg, 6/60, Chem 6, etc) on automated equipment and the cost is the same for one or both measures.

GUIDELINE 5

Frequency of Measurement of Kt/Vurea, Total CCr, PNA, and Total Creatinine Appearance (Opinion)

After 6 months, total Kt/Vurea , total CCr , and PNA (with all its components) should be measured every 4 months, unless the prescription has been changed or there has been a significant change in clinical status (see Table II-2).

Rationale Despite the establishment in 1993 of ESRD Network/Health Care Finance Administration guidelines that measurements of delivered PD dose and total solute clearance be performed twice yearly, a Network Core Indicator review of 1,208 patient charts in 1995 revealed that data sufficient to calculate such measures were available for only one third of the patients. The preliminary 1996 results reveal that 69% of the patient charts have such data (Diane Frankenfield, a member of the HCFA/HSQB ESRD Core Indicators PD Subcommittee, written communication, December 4, 1996; also available on the Internet at http://www.hcfa.gov/medicare/hsqb/hsqb1.htm).

Table II-2. Peritoneal Dialysis Dose and Total Solute Clearance Measurement Schedule After 6 Months

PD Fluid Urine*

Month

Kpt/Vurea CCr p Krt/Vurea CCr r

7

         
8       X† X†
9          
10 X X   X X
11          
12       X† X†
13          
14 X X   X X

NOTE. X, measurement.

* If incremental PD is still being utilized at this point, the frequency of RKF testing applies as described in Table 1 of Guideline 3: Frequency of Delivered PD Dose and Total Solute Clearance Measurement Within Six Months of Initiation. For patients who void infrequently (<3 times in 24 hours), collect urine over a 48-hour period. Urine testing can cease when the residual kidney function component is a weekly Krt/Vurea < 0.1.

† For young children who have greater difficulty with accurate urine collection than adults, this may be deferred until full urine and dialysate collections occur every 4 months (see Guideline 11: Dialysate and Urine Collection).



Measurements of delivered PD dose and total solute clearance are easy to perform, but require attention to detail and precision in technique for patients and dialysis staff. A variety of clinical and psychosocial events can interrupt and invalidate these measurements. It is imperative that these measurements become a routine for the patients and facility staff. Setting a goal of performing measurements every 4 months builds flexibility and leeway into a complex care plan, while assuring that a lengthy interval of possibly inadequate PD does not occur. The 4-month interval between complete measurements of total Kt/Vurea, total CCr, and PNA is recommended because it strikes a balance: every 4 months is often enough to be clinically helpful, but not so often as to be intrusive into a patient’s lifestyle or to create a burden for the dialysis facility. Awareness of loss of RKF must be paramount. If "incremental" PD is initiated instead of "full dose" (see Guideline 1: When to Initiate Dialysis–Kt/V Criterion, and Appendix A: Detailed Rationale for Guideline 1), RKF must be followed carefully and frequently such that PD dose can be increased as RKF deteriorates. While urine production rate is presumed to be a clue to deteriorating RKF, that is not always the case.21 Thus, for patients initiating PD with "incremental" PD, the Work Group recommends measuring RKF every 2 months (see Table II-2). For patients on "full dose" PD, the Work Group recommends measuring RKF with total solute removal measurements every 4 months. If urine production rate is decreasing, measure RKF every 2 months, or as often as needed and considered helpful, but at least every 4 months. Once weekly Krt/V falls to less than 0.1, RKF can be considered negligible and its routine measurement can be stopped. Guideline 11: Dialysate and Urine Collections, addresses this subject again.

The impact of a change in prescription should be assessed within 2 to 4 weeks in order to determine if the recommended change has actually been executed and if it has accomplished its goal. The promptness of the assessment is important because clinical events could occur in the interval which could postpone the measurement or confound the results (see Guideline 10: Timing of Measurement).

Some clinical events may impair the quality of delivered PD. A change in clinical condition which warrants measurement of delivered PD dose is defined as any serious problem which affects nutritional status, the ability of the patient to perform PD mechanically or technically (such as stroke or arthritis, loss of surface area from surgery, decreased exchange volumes due to hernias, etc), or permanently affects the transport properties of the peritoneum (eg, protracted peritonitis).22 Many conditions that lead to hospitalization fall into one of these categories. Any suggestion of exacerbation of uremia should prompt a measurement of delivered dose of PD.

The Work Group recognizes that technical problems in urine collections in some children may justifiably decrease the frequency of urine collections in selected cases.

GUIDELINE 6

Assessing Residual Kidney Function (Evidence)

Residual kidney function (RKF), which can provide a significant component of total solute and water removal, should be assessed by measuring the renal component of Kt/Vurea (Krt/Vurea) and estimating the patient’s glomerular filtration rate (GFR) by calculating the mean of urea and creatinine clearances.

Rationale A detailed rationale is presented in Appendix C. The following is a summary.

During the first few years of dialysis therapy, residual kidney function (RKF) contributes significantly to total solute and water removal. Preservation of RKF may be particularly important to the effectiveness of long-term PD. For solute removal targets to be met (see Guideline 15: Weekly Dose of CAPD, and Guideline 16: Weekly Dose of NIPD and CCPD) in many patients without a possibly unacceptable dialytic burden, there must be a substantial contribution from RKF.

As GFR declines over time, the contribution of secreted creatinine to total creatinine clearance (CCr) rises disproportionately and CCr becomes an inaccurate marker of GFR. Since the peritoneal membrane does not secrete solute, the GFR measure that corrects for creatinine secretion is the preferred measure to add to peritoneal clearance. In the case of a low GFR, the measurement of GFR with endogenous solutes is best done by defining GFR as the arithmetic mean of urea and creatinine clearance. This arithmetic mean essentially corrects for secretion of creatinine. This GFR measure is added to peritoneal CCr, normalized to 1.73 m2 of body surface area and is totaled for a week. This is the "total weekly creatinine clearance."

GFR(mL/min)=(kidney urea clearance(mL/min)+kidney creatinine clearance(mL/min))/2

Total weekly CCr=GFR+Peritoneal CCr normalized to 1.73 m2 of Body Surface Area

The MDRD study derived two equations which may approximate GFR,23 which are noted in Appendix C.

An alternative measure of RKF is residual renal urea clearance, normalized to total body water, Krt/Vurea. This measure can be directly added to the peritoneal urea clearance component, Kpt/Vurea, to create the total urea clearance normalized to total body water, Kprt/ Vurea (shortened to Kt/Vurea).

Creatinine clearance corrected for renal secretion and Kt/Vurea are both valuable measures in the management of PD patients. Each measure offers different information. Since the dialysate and urine collections are being performed for either measure, the Work Group recommends that both measures be determined.

GUIDELINE 7

PD Dose Troubleshooting (Opinion)

In adult patients, a daily creatinine excretion in urine and dialysate that differs from the baseline rate (as determined during the first 6 months in Guideline 3, Table II-1) by >15% should prompt an investigation for noncompliance, improper collection of drained dialysate and/or urine, or altered peritoneal transport function. Compliance should not be assessed by comparing measured to predicted creatinine excretion.

Rationale Twenty percent of PD patients report some noncompliance with their dialysis prescription.3 Preliminary data suggest that total daily creatinine excretion or appearance can be used as an indicator of compliance in CAPD. The premise for such use is that, in noncompliant patients who perform the proper number of exchanges only during the day of the clearance measurement,24 the amount of creatinine excreted in 24 hours (equal to the daily amount of creatinine in the spent dialysate and urine plus an estimated amount of creatinine lost through other routes, primarily the gastrointestinal tract) will exceed the amount of creatinine produced daily. Essentially, noncompliance creates an unsteady state of recently accumulated creatinine. Thus, an increase in the daily excretion of creatinine in dialysate plus urine may indicate noncompliance just prior to the collection.25 Other potential causes of variation in the measured amount of creatinine excreted include changes in muscle mass (see Guideline 13: Determining Fat-Free, Edema-Free Body Mass), improper collection of dialysate or urine due to timing errors, and inaccurate urine or dialysate creatinine measurement by the laboratory.25 Finally, another potential cause of change in total creatinine excretion may be peritoneal membrane transport dysfunction. Quantitatively, a very large transport defect must occur to result in 15% variation in the daily creatinine excretion. However, if this is suspected, a peritoneal equilibration test (PET) or its alternative should be performed.

A similar approach should be considered in children, although only a small number of pediatric patients have been studied in this manner.26 Furthermore, in growing children with increasing muscle mass, there will be an increase in total creatinine excretion over time.

The Work Group’s decision to use a variance of >15% in creatinine appearance over the established baseline was based on convincing but indirect evidence in adult patients. There are no data to support a similar approach in children. In PD patients who appear to be stable, creatinine appearance may vary by up to 15%, depending on a variety of factors.27 This variance of >15% is simply a suggestion or warning to the clinician that the creatinine excretion data are not consistent with prior evaluations and suggests a need for further investigation. The intensity of the investigation that the variance triggers is a clinical decision that requires taking many issues into consideration.

The Work Group does not recommend assessing compliance by comparing measured creatinine excretion to predicted creatinine excretion. Our reasoning is as follows: The estimated amount of creatinine lost in the gut is equal to 0.036 _ serum creatinine concentration in mg/dL _ body weight.28 The predicted creatinine production, in mg/day, is calculated by the Cockroft-Gault formulae29 as follows:

For men: [28 - (0.20 × Age)] × Weight

For women: [24-(0.17 × Age)] × Weight

where age is in years and weight is in kilograms.24,30,31 These formulae were derived in a nondialysis population. The discrepancy between measured and predicted creatinine generation is expressed as the ratio of measured/predicted creatinine generation.24

The use of a cut-off value of measured/predicted creatinine generation to identify noncompliance is not warranted because the measured/predicted creatinine generation in compliant CAPD patients appears to vary widely.24,32,33 In addition, the increase in the amount of creatinine excreted during the clearance day in noncompliant patients is very small in most cases.34-36 Measured/predicted creatinine generation is better used sequentially in a patient after establishing baseline values during a period of close observation (see Table II-1).32,36 At least for short periods of time (days or weeks), the steady-state excretion of creatinine is constant in CAPD patients,33,37 although a variation of 15% may be essentially physiologic.27 However, since absolute creatinine excretion is being measured and compared to a previously established reliable baseline measurement, the Work Group considers the use of predicted creatinine production to be unnecessary.

In summary, the Work Group recommends establishing a baseline creatinine excretion on the basis of 2 to 3 measurements in the first 6 months of PD (see Guideline 3: Frequency of Delivered PD Dose and Total Solute Clearance Measurement Within Six Months of Initiation). The Work Group feels that following these measures longitudinally will be more helpful than comparing measured to predicted creatinine appearance. Causes for any subsequent deviation from the baseline total creatinine excretion over time should be sought, recognizing that noncompliance is only one of several possible explanations.

RECOMMENDATIONS FOR RESEARCH

Since preservation of RKF is important for solute removal and contributes to total renal replacement therapy, there is a need to identify contributors to loss of RKF. For example, do antibiotics play a role? Hypotension? Other factors? Does aggressive solute removal and/or highly efficient dialysis remove stimulatory factors favoring remnant kidney hyperfiltration?

Why does GFR vary so much on a day-to-day basis and how does one account for this in adequacy studies? Is this a collection artifact or true physiologic variation? What factors alter the daily production and excretion of creatinine? Is it a function of creatinine production or simply excretion? If the latter, is it variation in renal secretion, filtration, or both? Urine output also varies dramatically on a day-to-day basis. Is this simply a volume phenomenon or is it a reflection of true clearance changes? Why does creatinine appearance vary even in compliant patients? Inchildren who are growing, how often should total creatinine excretion be measured and is it useful as an assessment of compliance with dialysis prescription?

The recommendation that >15% variance in creatinine appearance be considered as indicative of a status change or noncompliance should be validated.

An accurate, reproducible, and easy-to-perform method of measuring RKF should be developed.


 

 

 

 

 

 

 


© 2001 National Kidney Foundation, Inc

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