VIII. Appendices


Copies of the RPA’s Clinical Practice Guideline on Adequacy of Hemodialysis may be obtained by contacting:
Renal Physicians Association
4701 Randolph Road
Suite 102
Rockville, MD 20852
(301) 468-3515; (800) RPA-7525;
FAX (301) 468-3511
E-mail: rpa@renalmd.org


In formal UKM, the volume of distribution of urea (V) is calculated using computational software. The kinetic determination of V is based on the assumption of a single pool of urea that is coextensive with total body water and that expands during the interdialytic interval from fluid retention and contracts during hemodialysis by ultrafiltration. Assuming a thrice weekly hemodialysis schedule, the computational software reiterates the following two formulae until unique values are found to satisfy both expressions.

In Formula 1, Vt is the end dialysis volume; Qf is the rate of volume contraction during dialysis that is calculated from total weight loss during dialysis divided by the length of dialysis, t; G is the interdialytic urea generation rate; K and Kr are the dialyzer and kidney urea clearances, respectively; and Ct and C0 are the BUN concentrations at the end and beginning of a dialysis treatment. In Formula 2, α is the rate of interdialytic volume expansion and is calculated by the total interdialytic weight gain divided by the length of the interdialytic interval, θ.


1. Gotch FA: Kinetic modeling in hemodialysis, in Nissenson AR, Fine RN, Gentile DE (eds): Clinical Dialysis (ed 3). Englewood Cliffs, NJ, Prentice Hall, 1995, pp 156-189


The anthropometric volume of distribution of urea may be calculated by one of several formulae derived from stature, age, and gender-specific estimates of total body water (TBW) in healthy subjects.1,2

The Watson formulae are:

[Males]: TBW = 2.447 + (0.09516 × age) + (0.1074 × height) + (0.3362 × weight) (3)

[Females]: TBW = -2.097 + (0.1069 × height) + 0.2466 × weight (4)

The Hume-Weyer formulae are:

[Males]: TBW=(0.194786 × height) + (0.296785 × weight) -14.012934 (5)

[Females]: TBW=(0.34454 × height)+(0.183809 × weight) -35.270121, (6)

where TBW is total body water.

Because these formulae were derived from analyses performed in healthy adults, their general applicability to ESRD patients has been questioned. Based on measurements of total body water using bioelectrical impedance (BEI) in ESRD patients, a population-specific equation for calculating total body water was derived.3 In comparison to the Watson and the Hume-Weyers formulae, the BEI-derived formula for ESRD patients (Formula 7) correlated better with TBW as measured by BEI. Both the Watson and the Hume-Weyers formulae underestimated TBW (~7.5%), so may overestimate the delivered dose of hemodialysis.

TBW- =-0.07493713 × age

-1.01767992 × male + 0.12703384 × ht

-0.04012056 × wt + 0.57894981

× diabetes×0.00067247_wt2

-0.0348146×(age × male)

+0.11262857×(male × wt)

+0.00104135×(age × wt) + 0.0186104

×(ht × wt), (7)

where Wt and ht are the patients weight and height, respectively. Males and diabetics are assigned input values of 1.0. For pediatric patients, the Mellits-Cheek formulae are4:

[Males] TBW =-0.927+(0.465 × weight)+(0.045 × height), when heightų< 132.7 cm. (8)

TBW = -21.993 + (0.406 × weight)+(0.209 × height), when height > 132.7 cm. (9)

[Females] TBW = 0.076 + (0.507 × weight)+(0.013 × height),when heightų < 110.8 cm. (10)

TBW=-10.313+(0.252 × weight)+(0.154 × height),when height>110.8 cm. (11)


1. Watson ID, Batt RD: Total body water volumes for adult males and females estimated from simple anthropometric measurements. Am J Clin Nutr 33:27-39, 1980

2. Hume R, Weyers E: Relationship between total body water and surface area in normal and obese subjects. J Clin Pathol 24:234-238, 1971

3. Chertow GM, Lowrie EG, Lew NL, Lazarus JM: Development of a population-specific regression equation to estimate total body water in hemodialysis patients. Kidney Int 51:1578-1582, 1997

4. Jabs K, Warady BA: The impact of the Dialysis Outcomes Quality Initiative guidelines on the care of the pediatric end-stage renal disease patiuent. Adv Renal Replace Ther 6:97-106, 1999


Because of the short duration of impact, urea clearance provided by residual kidney function (Kr) contributes little to the intradialytic drop in BUN concentration (K [dialyzer clearance] > Kr). However, the long interdialytic interval more fully reveals the impact of Kr, which is manifest in the predialysis BUN concentration and the normalized protein catabolic rate (NPCR). The predialysis BUN concentration is lowered, and the NPCR is reduced. When Kr is zero, the interdialytic rise in the BUN concentration is linear; if Kr > 0, the rise in BUN will be more shallow and curvilinear resulting from continuous kidney urea excretion. Because Kr is continuous, whereas urea clearance by hemodialysis is intermittent, the basic relationships between the components of the dialysis treatment will not be modified. Thus, when the Kr > 0, the inter!-!dialytic rise in BUN is more shallow; less hemodialysis is required to achieve the same predi!-!alysis BUN concentration in comparison to when Kr = 0.

Quantitative relationships between Kr, and the decrease in the hemodialysis dose required to achieve identical predialysis BUN concentrations in the absence and presence of residual kidney function can be developed in a simplified form for hemodialysis prescription calculations by the formula:

kKr = Kt - K´t

K and K´ are the dialyzer urea clearances in the absence and presence of residual kidney urea clearance, respectively, and t is the duration of hemodialysis. In this formula, k relates Kr to the difference between K and K´, or the decrease in dialysis that is possible while still achieving the same predialysis BUN concentration that would be expected when there is no residual kidney urea clearance. k has units of L/mL/min and permits direct expression of Kr in equivalent liters of urea clearance provided by the dialyzer that can be spared. Thus, the relationship between the total dialysis dose (KT), the dose provided by the dialyzer (Kt), and the contribution of residual kidney urea clearance (kKr), are expressed by

KT/Vt × Kt/Vt + kKr/Vt.

Routinely solving these equations requires the use of computational software.


1. Gotch FA: Kinetic modeling in hemodialysis, in Nissenson AR, Fine RN, Gentile DE (eds): Clinical Dialysis (ed 3). Englewood Cliffs, NJ, Prentice Hall, 1995, pp 156-189

2. Yeun JY, Depner T: Principles of hemodialysis, in Owen WF, Pereira BJG, Sayegh M (eds): Dialysis and Transplantation (ed 1). Philadelphia, PA, Saunders, 1999, pp 1-21


Dialyzer Clearance (K) < Prescribed

Elements include: Dialyzer permeability (KoA), effective dialyzer surface area, effective blood flow, and effective dialysate flow.

Effective Dialyzer Clearance

1. Fistula/Graft Recirculation

If suspected:

Perform hydraulic compression test during dialysis.

If positive:

Perform Fistula/Graft Recirculation Study with low flow or stop flow technique.

If recirculation is present:

Revise graft/fistula.

Needle placement and orientation of needle

Needles placed in same direction and close proximity?

If true:

Orient staff about different needle orientation.

Document needle placement with each dialysis.

Verify graft flow direction.

If current knowledge is incorrect:

Document arterial and venous limbs in chart/Kardex.

Document A/V needle placement on flow sheet.

2. Dialyzer clearance overestimated (dialyzer permeability KoA is less than manufacturer’s specifications)

If suspected:

Check kinetic modeling results on other patients using dialyzer, specifically the kinetic volume of distribution.

If consistent finding:

Check with manufacturer for current data.

If KoA is different:

Correct KoA in prescription and calculate new Rx with new dialyzer clearance.

3. Dialyzer effective surface area reduced

If suspected:

Check for correlation of total cell volume (TCV) with kinetic modeling results, specifically the kinetic volume of distribution.

If there is a correlation:

Document results of visual inspection of the dialyzer after dialysis.

Review and correct anticoagulation.

Review reuse procedures.

If there is an obvious problem:

Correct reuse procedures.

Add heparin to post dialysis flush and recirculation after patient is disconnected from circuit.

Errors in Blood Flow Rate (Qb)

1. Inaccurate blood pump calibration

If suspected:

Review last record/date/data from pump calibration.

Check kinetic results on patients using the same piece of equipment.

If calibration is inaccurate:

Recalibrate blood pump.

2. Inadequate blood pump occlusion

If suspected:

Review last record/date/data from pump calibration and occlusion.

Review documented extracorporeal pressures for the dialysis.

Review pressure specifications for occlusion of the blood pump.

Check kinetic results on patients using the same piece of equipment.

If there appears to be a pump occlusion problem:

Recheck/correct pump occlusion.

3. Reduced blood pump stroke volume

If suspected:

Measure volumetric "blood" flow rates on the equipment at the extremes of extracorporeal pressures seen in the patient/unit.

Check variability in blood tubing specifications for cross-sectional area and wall thickness.

If problem exists:

Correct dialysis prescription for lower Qb.

Check for prepump tubing segment collapse with negative prepump arterial pressure.

Review documented extracorporeal pressures, especially the prepump pressures.

If problem is seen:

Correct the dialysis prescription for lower Qb.

Check blood tubing wall thickness requirements with manufacturer.

4. Error in blood pump setting–reduced or lower setting than Rx

If suspected:

Check dialysis log sheet for clinical problems/symptoms.

If present:

Reorient patient and staff to need to maintain Qb as prescribed if possible.

Check for extracorporeal pressure problems.

If present:

Consider the use of different needle gauge.

Review needle placement and orientation.

Check hematocrit and ultrafiltration requirements.

If high:

Consider larger needle gauge.

If any problems present:

Correct the dialysis prescription for a lower Qb.

Error in Dialysate Flow Rate (Qd)

1. Inaccurate dialysate flow calibration

If suspected:

Review last record/date/data on machine calibrations.

If problem:


2. Error in dialysate flow setting

If present:

Standardize documentation of Qd.

Treatment Time (t) < Rx

Effective treatment time is the actual dialysis time at the prescribed blood and dialysate flow rates.

1. Inadequate measurement method

• Automated with equipment

If problem:

Document time from equipment on dialysis log sheet.

• Manual method

If problem:

Review time measurement with staff.

Standardize measurement method and recording method and form for recording.

2. Numerous treatment interruptions

If suspected:

Review dialysis log sheets for events (and duration) such as dialyzer blood leaks, needle problems, and pressure problems. If problem:

Standardize documentation of events.

Standardize documentaiton of the amount of time lost.

Reorient patients and staff to the importance of delivering the prescribed dialysis time.

3. Early termination of treatment

If suspected:

Check for documentation and reasons of early termination.

Check for documentation of the amount of time lost.

If problem:

Review frequency of early termination with patients and staff.

Review reasons for early termination with patients and staff.

Attempt to correct depending on findings.

Unit policy.

If frequent problem:

Review unit policy and reformulate as necessary.

4. Elective shortening of treatment

If suspected:

Check for persistent late arrival of patient.

If problem:

Review data with patient and problems with shortening treatments.

Discuss risks with patient.

Evaluate transportation needs of patient.

Staff/unit convenience.

If problem:

Review data with staff and problems with shortening treatments.

Discuss risks with staff.

Review Rx importance.

Errors in BUN Concentration Predialysis BUN Sample Concentration Low

1. Saline-filled needles used

If problem:

Use dry needles for sample.

Withdraw 10 mL from fistula needle before drawing sample.

2. Sample drawn after dialysis has started

If problem:

Review proper sample procedure with staff.

3. Laboratory procedure–high BUN value extrapolated from standards (BUN values of 99 or 98 mg/dL are seen often)

If problem:

Request dilution of samples with BUN >90 mg/dL.

Postdialysis BUN Sample Concentration High

1. Sample drawn late (>5 minutes after end of treatment–urea rebound)

If suspected:

Review sampling procedure relative to unit-approved procedure.

Standardize sampling time and technique.

2. Laboratory error

If suspected:

Check calibration range on equipment.

Pre/post samples analyzed on the different equipment or apparatus run.

If problem:

Request that pre/post dialysis samples be analyzed with same equipment and on the same analytic run.

3. Bloodlines/needles reversed

If suspected:

Check graft configuration.

Check for needle placement.

If problem:

Document graft configuration for staff.

Review needle placement and orientation with staff.

Postdialysis BUN Sample Concentration Low

1. Fistula recirculation

If suspected:

Reduce Qb to 50 to 100 mL/min before sampling.

Clear arterial bloodline/fistula needle tubing with syringe before drawing sample.

2. Sample diluted with saline from reinfusion

If suspected:

Review sampling procedure with staff.

Standardize sampling procedure.

3. Sample drawn from venous bloodline port

If suspected:

Employ methods/techniques to reduce the incidence, eg, educate patient to observe sampling period.

Fig I-3. Illustration of the hydraulic pressure tests for graft assessment and the potential outcomes. During hemodialysis, prepump and postdialyzer pressures are noted and recorded. The central body of the graft is then manually occluded between the two needles. Pressure changes may be indicative of a problem. However, the absence of pressure changes does not eliminate the possibility of a problem. Reprinted with permission of American Nephrology Nurses Association.


Prepump and postdialyzer pressure changes observed with manual graft occlusion between the two needles during dialysis has been useful in identifying stenotic lesions in grafts. Prerequisites to use the hydraulic test of the graft are that: (1) the needles are oriented toward the respective vascular anastamoses; (2) the main channel of the access is cannulated; (3) prepump arterial pressure is monitored; (3) there is enough space between the needles to place 1 or 2 fingers for access occlusion; and (4) no compression of the feeder artery occurs during the occlusion. The hydraulic pressure test is performed as described.

1. During dialysis at the desired blood flow rate, extracorporeal pressures are noted and recorded.

2. The central body of the graft (between needles) is completely occluded for sufficient time to observe for any pressure changes.

3. The pressures changes are recorded.

4. If the graft is fully patent, the pressures will move towards zero with occlusion will move toward zero (arterial pressure less negative and venous pressure less positive). If an arterial stenosis is present, graft occlusion results in a significant increase in the prepump arterial pressure (becomes more negative). If no prepump arterial pressure monitor is available, observe the arterial bloodline to detect any increase in rhythmic motion from the pump rotations. If a venous stenosis is present, an increase in the postdialyzer venous pressure is observed (becomes more positive). These changes are illustrated in Fig I-3.


1. Daniels ID, Hoffer EK, George-Cipriani JA, Friedman EA, Lundin AP: Clinical tests detect hemodialysis access stenosis. J Am Soc Nephrol 4:32, 1993





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