NKF K/DOQI GUIDELINES 2000
GUIDELINES FOR PERITONEAL DIALYSIS ADEQUACY
III. Measurement of Peritoneal Dialysis Dose
Reproducibility of Measurement (Opinion)
Accurate measurement of total Kt/Vurea and total creatinine clearance (CCr) requires collection and analysis of urine, dialysate, and serum in a way that yields reproducible and valid results. Dialysate creatinine concentration must be corrected for the presence of glucose in some assays. Peritonitis precludes reliable measurement of delivered PD dose for up to a month. Compliance with complete collections is mandatory. For patients who void Ù3 times per day, a 24-hour urine collection is sufficient. For patients who void less frequently, a 48-hour collection is recommended. For CAPD patients, the serum sample can be obtained at any convenient time. For NIPD patients, the serum sample should be obtained at the midpoint of the daytime empty period. For CCPD patients, the serum sample should be obtained at the midpoint of the daytime dwell.
Rationale A detailed rationale is presented in Appendix D. The following is a summary.
Measurement of PD dose must be performed in a valid and reproducible fashion. The measure of creatinine concentration in effluent dialysate must be corrected for the presence of glucose with some creatinine assays. Each facility must determine whether this is necessary by specifically inquiring of its laboratory whether the creatinine assay used by that lab is altered by high glucose concentrations. PD dose measures should not be made until a month after peritonitis resolves, because peritonitis causes residual effects on membrane transport. Either total dialysate collections or aliquots (ie, samples of dialysate) can be used with proper patient training and compliance. For CAPD patients, the timing of the blood sample is not important. For patients on NIPD or CCPD, the blood sample must reflect the overall average for the entire 24 hours. For NIPD patients, the serum sample should be obtained at the midpoint of the daytime empty period. For CCPD patients, the serum sample should be obtained at the midpoint of the daytime dwell. For most NIPD and CCPD patients, these time points occur in the early afternoon.
Estimating Total Body Water and Body Surface Area (Opinion)
V (total body water) should be estimated by either the Watson38 or Hume39 method in adults using actual body weight and by the Mellits-Cheek method38 in children using actual body weight.
For Men: V (liters) = 2.447 + 0.3362*Wt (kg) + 0.1074*Ht (cm) - 0.09516*Age (years)
For Women: V = -2.097 + 0.2466*Wt + 0.1069*Ht
For Men: V = -14.012934 + 0.296785*Wt + 0.194786*Ht
For Women: V = -35.270121 + 0.183809*Wt + 0.344547*Ht
Mellits-Cheek method for children40:
For Boys: V (liters) = -1.927 + 0.465*Wt (kg) + 0.045*Ht (cm), when Ht < 132.7 cm
V = -21.993 + 0.406*Wt + 0.209*Ht, when height is > 132.7 cm
For Girls: V = 0.076 + 0.507*Wt + 0.013*Ht, when height is < 110.8 cm
V = -10.313 + 0.252*Wt + 0.154*Ht, when height is > 110.8 cm
Body surface area, BSA, should be estimated by either the DuBois and DuBois method,41 the Gehan and George method,42 or the Haycock method43 using actual body weight.
For all formulae, Wt is in kg and Ht is in cm:
DuBois and DuBois method: BSA (m2) = 0.007184*Wt0.425*Ht0.725
Gehan and George method: BSA (m2) = 0.0235*Wt0.51456*Ht0.42246
Haycock method: BSA (m2) = 0.024265*Wt0.5378 *Ht0.3964
Rationale A detailed rationale is presented in Appendix E. The following is a summary.
The Watson and Hume formulae were derived by comparing total body water measurements to simple anthropometric measurements (weight, height, age) in subjects without edema, volume deficit, or end-stage renal disease. In peritoneal dialysis patients, the Watson and Hume formulae provide reasonable approximations of isotopic body water measurements. Volume abnormalities (edema) are apparently the major cause of discrepancy. The Mellits-Cheek formulae were derived from subjects aged 1 month to 34 years for males and 1 month to 31 years for females. In each case, the measurement of total body water was performed in normal subjects by the use of deuterium oxide distribution, with simultaneous measurement of weight and height.
The Work Group recommends the use of the Watson or Hume formulae in adults and the Mellits-Cheek formula in children as methods for estimating V. Attention should be paid to the presence of edema at the time of the clearance study. A special case is the underweight patient. (See Table II-1, Appendix E for a definition.) Successful efforts to restore weight to a normal level in such a patient will result in a rising V and consequently in a proportionally declining Kprt/Vurea. This does not alter the methodology of estimating total body water using actual weight. It does affect target doses of dialysis, however. This issue is discussed again in Guideline 15: Weekly Dose of CAPD.
Like the formulae given above for total body water, the formulae for BSA were determined in a normal population. Many of the disclaimers described for calculating V are less of an issue in calculating BSA, because the relationship to the defining simple anthropometric measurements is less influenced by clinical conditions accompanying ESRD. Historically, many nephrologists have utilized the method of DuBois and DuBois, and much of our data are from its application. Only 9 subjects were used to define this formula.41 More than 400 subjects, including many children, were used to define the formula of Gehan and George,42 and in an independent comparison, the Gehan and George method was preferred.44 The Haycock formula is based on measurements of 81 subjects ranging from premature infants to adults.43
Amputation alters the relationship between body height and weight. This causes a mathematical distortion of the calculation of both anthropometric V and BSA, because the calculation of each takes this relationship into account.45,46 Modification of V and BSA in patients with amputations are described in detail in Appendix E.
Timing of Measurement (Opinion)
Routine measurements of total Kt/Vurea and total creatinine clearance should be performed when the patient is clinically stable (eg, stable weight, stable BUN and creatinine concentrations) and at least 4 weeks after resolution of peritonitis.
Following a change in prescription or a major change in clinical status (eg, hospitalization, weight loss), but in the absence of recent peritonitis, measurements of delivered weekly Kt/Vurea and total weekly CCr should be performed within the next 4 weeks and then at 4-month intervals.
Rationale The effect of body weight on the calculation of V is discussed in the rationale for Guideline 9: Estimating Total Body Water and Body Surface Area, and in Appendix E: Detailed Rationale for Guideline 9. Variations in serum urea and creatinine concentration can potentially increase the error in the clearance calculations and indicate that the patient is not in a steady state.
Peritonitis may, in some instances, affect peritoneal solute transport for long periods. The rationale for waiting 4 weeks after resolution of peritonitis to repeat the clearance studies is presented in Appendix D: Detailed Rationale for Guideline 8.
The Work Group recommends frequent assessment of delivered dose of PD and total solute clearance, specifically every 4 months after the first 6 months of PD (see Guideline 11: Dialysate and Urine Collections). Major changes in clinical status (eg, patient compliance, weight gain, weight loss, technical/mechanical complications, some causes of hospitalization) may alter PD dose requirements. For example, pneumonia may contribute to loss of residual kidney function, which would be undetected unless measured. Therefore, in the absence of peritonitis, a major change in clinical status should prompt a re-evaluation of weekly Kt/Vurea and total weekly CCr, and this should occur within 1 month following the change in clinical status. Within 1 month following a PD prescription change, weekly Kt/Vurea and total weekly CCr should be measured to demonstrate that the goals of the prescription change have been achieved. If the patient is not stable, all attention should be directed to determining the cause of the instability and to correcting it. This may or may not include measuring the delivered dose of PD. There will be circumstances in which the change in clinical status might only alter RKF (eg, exposure to nephrotoxins), not delivered dose of PD. While one must be cautious in assuming that persistent urine flow rate implies stable RKF,21 a clinical clue that deterioration has occurred may be a decrease in what previously had been a stable daily urine volume.47 In those settings, only measurement of RKF is indicated.
Dialysate and Urine Collections (Opinion)
Two to three total solute removal measurements are required during the first 6 months of PD (see Guideline 3: Frequency of Delivered PD Dose and Total Solute Clearance Measurement Within Six Months of Initiation). After 6 months, if the dialysis prescription is unchanged:
1. Perform both complete dialysate and urine collections every 4 months; and
2. Perform urine collections every 2 months until the renal weekly Krt/Vurea is <0.1.
Thereafter, urine collections are no longer necessary, as the RKF contribution to total Kt/Vurea becomes negligible. In young children, urine collections are recommended only with complete dialysate collections (see Table II-2 reproduced from Guideline 5).
Rationale Loss of residual kidney function is the major cause of decreasing clearance in PD subjects followed longitudinally.48,49 The CANUSA study demonstrated substantial loss of kidney function at 6-month intervals.49 The Work Group concludes that measurements of urinary clearances should be performed at 2-month intervals to prevent long periods of underdialysis. For young children in whom urine collections are difficult (requiring special collection apparatus, etc), urine collections can be deferred until the next total solute removal measurement (see Guideline 3: Frequency of Delivered PD Dose and Total Solute Clearance Measurement within Six Months of Initiation, and Guideline 5: Frequency of Measurement of Kt/Vurea, Total CCr, PNA, and Total Creatinine Appearance).
RECOMMENDATIONS FOR RESEARCH
The optimal timing of blood sampling for subjects on asymmetric PD (NIPD, CCPD) should be determined. The recommendations we have made are based on pharmacokinetic theory.
Comparison of the "batch" and "aliquot" methods of dialysate sampling should be studied.
Development of a clinically applicable method of assessing TBW in children undergoing PD is recommended.
Methodology to calculate renal urea and creatinine clearance and PNA from random urine samples should be developed
© 2001 National Kidney Foundation, Inc