KDOQI Update 2000
 
NKF KDOQI GUIDELINES 2000
 
 

GUIDELINES FOR HEMODIALYSIS ADEQUACY

II. Hemodialysis Dose

GUIDELINE 4

Minimum Delivered Dose of Hemodialysis (Adults Evidence, Children Opinion)

The dialysis care team should deliver a Kt/V of at least 1.2 (single-pool, variable volume) for both adult and pediatric hemdialysis patients. For those using the URR, the delivered dose should be equivalent to a Kt/V of 1.2, ie, an average URR of 65%. However, URR can vary substantially as a function of fluid removal.

Rationale Numerous peer-reviewed studies have confirmed the association between the adequacy of the delivered dose of hemodialysis and patient outcome.19,33,34,36,38-42,57 At the time of its publication in 1993, the RPAžs Clinical Practice Guideline on Adequacy of Hemodialysis defined adequate hemodialysis as the recommended quantity of hemodialysis delivered which is required for adequate treatment of ESRD such that patients receive full benefit of hemodialysis therapy. At that time, the 15-year-old National Cooperative Dialysis Study (NCDS) was the sole prospective, randomized, controlled trial to provide data concerning the relationship between the fractional clearance of urea and patient outcome.34 Reanalysis of the primary data from the NCDS showed that Kt/V <0.8 was associated with a relatively high rate of patient morbidity, whereas Kt/V values between 1.0 and 1.2 were associated with a low rate of morbidity.48

Extrapolating from the NCDS data to current dialysis practice is difficult for several problems. The NCDS was performed prior to the widespread dissemination of current hemodialysis technologies such as ultrafiltration control, bicarbonate dialysate, variable dialysate sodium programming, and biocompatible dialysis membrane materials. Furthermore, patients with demographic characteristics similar to those of many current ESRD patients were not eligible for participation in the NCDS. For example, diabetics and patients over the age of 70 were excluded from the NCDS. Finally, morbidity, not mortality, was the principal outcome.34 Thus, the RPAžs Clinical Practice Guideline on Adequacy of Hemodialysis stated that the NCDS alone was not an appropriate guide regarding what constitutes the minimum dose of hemodialysis. The authors of the RPAžs Clinical Practice Guideline on Adequacy of Hemodialysis found that uncontrolled retrospective studies suggested an improved survival with greater delivered doses of hemodialysis (up to Kt/V >1.2 and URR of 65%).19,51,147

Table I-2. The Correlation of URR to Kt/V Corrected for Ultrafilitration

URR Values at Kt/V
ΔWt/BWt, %
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
0
53
57
61
65
68
71
74
76
1
52
57
61
64
68
71
73
76
2
50
55
59
63
66
69
72
75
3
49
54
58
62
65
68
71
74
4
48
53
57
61
64
67
70
73
5
47
51
56
60
63
67
70
72
6
46
50
55
59
62
66
69
71
7
44
49
53
58
61
65
68
71
8
43
48
52
57
60
64
67
70
9
42
47
51
56
63
65
66
69
10 41 46 50 54 58 62 65 68
NOTE. Calculated from single-pool, variable volume model with a body weight of 67.3 kg, V of 35 L, and NPCR of 1.0. Wt/BWt is the ultrafiltration volume divided by the postdialysis weight multiplied by 100.




Because literature available at the time of the RPAžs Clinical Practice Guideline on Adequacy of Hemodialysis was not definitive, a decision analysis was performed using available data.184 The initial analysis used a probabilistic model to assess how variables in the dialysis prescription affect a patientžs quality-adjusted life expectancy (QALE). In a complementary analysis, lifetime costs and QALE were modeled to determine the marginal cost-effectiveness of the components of the dialysis prescription. On the basis of this analysis, the RPA recommended that the delivered Kt/V should be at least 1.2. For those using URR, this value should be at least 65%. The RPAžs Clinical Practice Guideline on Adequacy of Hemodialysis noted that the QALE increases with increasing Kt/V to a tested level of 2.0. However, at Kt/V >1.3, a rapid increase in outpatient costs to achieve the higher dose of hemodialysis occurred in conjunction with improvements in QALE. Thus, the final RPA recommendation reflected a balance of concerns regarding the patients quality-adjusted life expectancy and marginal cost-effectiveness.

The HD Adequacy Work Group reviewed the literature available after the release of the RPAžs Clinical Practice Guideline on Adequacy of Hemodialysis and found no convincing basis for recommending a higher minimum dose of hemodialysis. Most of the published reports supporting the suggestion that hemodialysis patients benefit from higher minimum values of Kt/V or URR are retrospective observational analyses from self-selected hemodialysis centers, which could lead to selection bias and inability to generalize to other populations.33,40,41,147 Limitations of these reports include the comparison of patient outcomes to uncontrolled historical standards,41,147 lack of patient randomization,33,36,40 patient profiles that did not match prevalent ESRD patients,36 lack of standardization for collecting BUN samples,33,40 use of relatively broad categories of Kt/V or URR for analysis,33,40 or major differences in clinical practice and patient behaviors compared to those in the United States.147 Although one of these studies was prospective, patient randomization was not performed; several factors other than the dose of hemodialysis varied simultaneously; and the only comparison made was between an adequate and inadequate hemodialysis dose (Kt/V = 1.3 versus 0.8, respectively), ie, a minimum target Kt/V was set at the start of the study.36 The Work Group also felt that much of this literature was compromised by the longitudinal averaging of hemodialysis doses, rather than accounting for repeated measures within a single individual. In addition, the ability to draw conclusions from these studies is limited by their use of mean data.42 If the improvement in survival for ESRD patients occurs as a step function above some minimum Kt/V, increasing the dialysis dose for the population of patients will result in a decrease in mortality for the group. With a normal distribution, increasing the group mean minimizes the number of patients at risk, so the false impression of continued benefit from higher dialysis doses is portrayed. Furthermore, not all study results suggested that patient survival improved with delivered hemodialysis doses higher than Kt/V of 1.2 (URR of 65%).19 A recent retrospective analysis of data from the Case Mix Adequacy Database, which used both single-pool (sp) and double-pool (dp) urea kinetic models, found no improvement in survival for a Kt/Vsp of 1.2 to 1.4 or a Kt/Vdp of 1.0 to 1.2.185

In the absence of clear and consistent data demonstrating a clinical outcome advantage associated with a higher minimum dose of hemodialysis, the Work Group cannot advise that the minimum hemodialysis dose recommended in the RPAžs Clinical Practice Guideline on Adequacy of Hemodialysis be changed for adult patients with ESRD. However, dialysis care teams are not discouraged from establishing greater minimum levels of hemodialysis dose for their patients. In fact, because of variability in the measurement of delivered dose,183 as discussed in greater detail in Guideline 5: Prescribed Dose of Hemodialysis, higher minimum prescribed hemodialysis doses are encouraged. The HD Adequacy Work Group acknowleges concerns that some patients with a small V may develop deleterious metabolic disturbances in the setting of a high Kt/V or URR.186 Because this scenario has not been validated in outcome studies, and because the risk of inadequate hemodialysis is well-established, the Work Group underscores that these recommendations are minimum, not target values.

Adjustments of URR for ultrafiltration. In determining whether the recommended minimum dose of hemodialysis is delivered, the dialysis care team is reminded that the relationship between Kt/V and URR is affected by the extent of ultrafiltration141,142 (see Guideline 2: Method of Measurement of Delivered Dose of Hemodialysis, and Fig I-1). Table I-2 presents these relationships by illustrating the correlation between the single-pool Kt/V and the ultrafiltration volume as a function of the patientžs postdialysis weight.

Because of the variability due to ultrafiltration, when URR is used as the method for measuring hemodialysis adequacy, the minimum delivered dose should be equivalent to a Kt/V of 1.2 (ie, an average URR of 65%), but can vary substantially as a function of fluid removal.

Optimal dose of hemodialysis. The Work Group emphasizes that the literature clearly supports delivery of a minimum hemodialysis dose of at least Kt/V = 1.2, but does not suggest what constitutes an optimal dose. Identification of an optimal dose of hemodialysis would require evaluation of patient survival, the patientžs subjective valuation of quality of life, and the cost-effectiveness of hemodialysis. Until such data are available, the Work Group emphasizes that the hemodialysis doses recommended herein are minimum values only.

Minimum delivered dose in selected patients. The Work Group also evaluated the issue of defining a minimum dose of hemodialysis for selected patient subsets defined on the basis of demographic characteristics or comorbidity.

Other factors related to hemodialysis adequacy. The HD Adequacy Work Group reminds the hemodialysis care team that Kt/V and URR focus on only one of the numerous parameters that operationally define the adequacy of hemodialysis.14,39,110,147,159,190-192 Urea is only a marker solute47,83 and measures of hemodialysis adequacy, such as the Kt/V or URR, are only surrogates for the clearance of other small molecular weight solutes. As discussed in the introduction, the flux of larger molecular weight solutes and membrane biocompatibility may be equally important issues.88,89,91,107 The Work Group recognizes that an increasing body of evidence suggests that the clearance of larger molecular weight solutes may have an independent effect on patient survival that is not fully reflected in the Kt/Vurea. Therefore, the Work Group urges clinicians not to base the dose of hemodialysis for an individual patient solely on the minimum acceptable amount of urea removed in a single dialysis session. For example, even when an appropriate minimum Kt/V or URR is routinely delivered, a patient may still be inadequately dialyzed in terms of potassium removal, correction of acidosis, or failure to render the patient a sufficient protein/caloric intake to prevent malnutrition. Similarly, an appropriate minimum Kt/V or URR may be routinely delivered, but the duration of hemodialysis may be too short to remove an adequate volume of fluid to reestablish euvolemia. The issue of more global, outcome-based definitions of hemodialysis adequacy is especially important for pediatric ESRD patients. Attention should be given to the childžs school or vocational performance, growth, and emotional development, as well as the Kt/V.

Likewise, the dialysis care team is reminded that within the constraints of the desired Kt/V, the duration of dialysis should be a matter of shared decision making with the patient. If after full disclosure to the patient of the deleterious outcomes resulting from inadequate hemodialysis, the patient desires a dialysis duration that is insufficient, the dialysis care team should respect the patientžs wishes. However, a nonconfrontational dialogue should be continued regarding this topic. If a correctable barrier to adequate dialysis is identified, such as cramps or hypotension (see Guideline 16: Strategies to Minimize Hypotensive Symptoms), it should be addressed.

Twice-weekly hemodialysis. All HD Adequacy Work Group recommendations regarding hemodialysis dose are based on the assumption that hemodialysis treatments are delivered three times per week. Twice-weekly hemodialysis is usually inadequate unless there is a reasonable amount of residual kidney function (GFR ≥5 mL/min). Because residual kidney function declines with time, if a significant amount of kidney function is present at the initiation of hemodialysis, and the patient is undergoing twice-weekly hemodialysis, residual kidney function must be monitored serially. Such diligence guides the appropriate timing of a switch to three times per week hemodialysis. Unless close monitoring of the patientžs residual kidney function can be routinely and serially provided, the Work Group recommends hemodialysis three times per week for all patients who require hemodialysis.

GUIDELINE 5

Prescribed Dose of Hemodialysis (Opinion)

To prevent the delivered dose of hemodialysis from falling below the recommended minimum dose, the prescribed dose of hemodialysis should be Kt/V 1.3. In terms of URR, a Kt/V of 1.3 corresponds to an average URR of 70%, but the URR corresponding to a Kt/V of 1.3 can vary substantially as a function of ultrafiltration.

Rationale Not all patients receive their prescribed dose of hemodialysis.53-55,81,115,116 Some studies suggested that only 50% of ESRD patients in the United States actually receive their prescribed hemodialysis dose.115 To ensure that patients receive the minimum adequate dose of hemodialysis at all treatments, nephrologists should prescribe doses of hemodialysis that are higher than the aforementioned minimum delivered levels.

A variety of factors may result in the actual delivered dose of hemodialysis falling below the prescribed dose.53-55,60,81,115,116,183,193 Common factors include:

1. Compromised urea clearance. Effective urea clearance is a combination of dialyzer membrane permeability and surface area plus blood and dialysate flow rates. Effective clearance may be compromised by:

2. Reductions in treatment time. Effective treatment time must accurately reflect the exact amount of time during which diffusion occurred at the prescribed blood and dialysate flow rates. Reasons that effective treatment time may be less than the prescribed time include:

3. Laboratory or blood sampling errors. Predialysis and postdialysis BUN measurements may not reflect the true systemic urea concentration at the time hemodialysis was initiated and terminated, respectively, due to errors in sampling procedure and/or laboratory error. Reasons for errors in measurement of BUN concentration include:

The HD Adequacy Work Group emphasizes that most of the problems pointed out above will result in a discrepancy between the V derived from formal UKM and the V derived from anthropometrics. Therefore, these problems will be readily detected in a dialysis CQI program that uses formal UKM.

The Work Group was particularly concerned about the observed tendency within the nephrology community to implement the minimum Kt/V and URR values from the RPAžs Clinical Practice Guideline on Adequacy of Hemodialysis as target values. Because of the plethora of variables that adversely affect the delivered dose of hemodialysis, the deliberate targeting of a delivered Kt/V = 1.2 or a URR = 65% will result in a significant number of hemodialysis sessions in which the Kt/V or URR fall below these threshold values.

To prevent the Kt/V or URR for any patient from declining to values below the recommended minimum delivered dose, practitioners should prescribe doses of hemodialysis that are greater than these minimum values. A recent survey of hemodialysis practices demonstrated that a low dialysis prescription was one of the strongest predictors of inadequate dialysis dose.53 In the National Institutes of Healthžs (NIH) HEMO Study, where rigorous implementation of the hemodialysis prescription and measurements of the dose of hemodialysis have been effected,92 the 90% confidence interval for the single-pool Kt/V of 1.3 is 0.10 units (T. Greene, personal communication, 1999). Therefore, the Work Group suggests that the prescribed minimum Kt/V be 1.3 for patients dialyzing three times per week. For URR, the HEMO Study observed a 90% confidence limit of 4%. Therefore, nephrologists using URR should set a minimum target URR of 70% (T. Greene, personal communication, 1999). Different target values will be needed for patients who dialyze more or less frequently.


 

Table I-3 Values for Single Pool (spKt/V) Calculated From Equilibrated (eKt/V) and Dialysis Treatment Time (t)

spKt/V at eKt/V of
Hours 1.0 1.05
2.0 1.39 1.46
2.5 1.28 1.34
3.0 1.21 1.28
3.5 1.17 1.23
4.0 1.14 1.20
4.5 1.12 1.18
5.0 1.10 1.16


            Recognizing that some dialysis care teams may prefer to follow hemodialysis dosing using a double pool model for Kt/V, the HD Adequacy Work Group recommends that the minimum prescribed dose in a double pool model be considered to be 1.05 for patients dialyzing three times per week. In the HEMO Study, of 426 patients randomized, this minimum target resulted in fewer than 4% of the patients having a single pool Kt/V <1.2. As shown in Table I-3, if a eKt/V of 1.05 is prescribed, the spKt/V does not decrease to <1.2 until the hemodialysis time is increased to >4 hours. On the other hand, if an eKt/V of 1.0 is used, this relationship occurs at dialysis times >3 hours.

Evidence or suspicion that the delivered hemodialysis dose has fallen below the prescribed value should trigger a thorough evaluation of the processes involved in delivering dialytic care. Guideline 14: Inadequate Delivery of Hemodialysis, presents an algorithm for detecting the cause(s) of inadequate delivery of hemodialysis and for implementing corrective action.

GUIDELINE 6

Frequency of Measurement of Hemodialysis Adequacy (Opinion)

The delivered dose of hemodialysis should be measured at least once a month in all adult and pediatric hemodialysis patients. The frequency of measurement of the delivered dose of hemodialysis should be increased when:

1. Patients are noncompliant with their hemodialysis prescriptions (missed treatments, late for treatments, early sign-off from hemodialysis treatments, etc.).

2. Frequent problems are noted in delivery of the prescribed dose of hemodialysis (such as variably poor blood flows, or treatment interruptions because of hypotension or angina pectoris).

3. Wide variability in urea kinetic modeling results is observed in the absence of prescription changes.

4. The hemodialysis prescription is modified.

Rationale Numerous outcome studies have demonstrated a correlation between the delivered dose of hemodialysis and patient mortality and morbidity.19,33,34,36,38-42,57 The evidence demonstrates that mortality among ESRD patients is lower when an appropriate minimum dose of hemodialysis is provided. To ensure that ESRD patients treated with chronic hemodialysis receive adequate treatments, the delivered dose of hemodialysis needs to be measured. Clinical signs and symptoms alone are not reliable indicators of dialysis adequacy (see Guideline 1: Regular Measurement of the Delivered Dose of Hemodialysis).

The HD Adequacy Work Group recommends that the dose of hemodialysis be measured at least monthly. There are several reasons for this recommendation. In the studies of the relationship between delivered dose of hemodialysis and patient outcome, the typical frequency of performance of the selected measurement of the delivered dose of hemodialysis was monthly.19,33,34,36,38,39,41 Less frequent measurement may compromise the timeliness with which deficiencies in the delivered dose of hemodialysis are detected and, hence, may delay implementation of corrective action. Furthermore, the Work Group noted that most ESRD patients undergo monthly blood-based biochemical evaluations and that the institutional reporting of the results occurs monthly. Therefore, monthly measurement of delivered dose is pragmatic. There is neither evidence nor reason to believe that pediatric and adult patients differ in their need for adequate hemodialysis or their need for at least monthly assessment of the delivered hemodialysis dose.

RECOMMENDATIONS FOR RESEARCH

Observational data should be collected on the relationship between the frequency of measurement of hemodialysis adequacy and patient outcomes and costs of care.

 

 

 

 

 


© 2001 National Kidney Foundation, Inc

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