Rationale for Guideline Kt/V urea Targets for Hemodialysis

Hemodialysis Adequacy (Kt/V) Targets

Contribution from European Best Practice Guidelines Committee

The current 2002 version of the European Best Practice Guidelines recommend:

Dialysis dose should be quantified as equilibrated Kt/V (eKt/V).
EKt/V should be quantified using the Gotch model with a 30 minute post-HD blood urea or an immediate post-HD urea and corrected for the post-dialysis rebound.
The minimum eKt/V should be 1.2.

The guideline is currently being updated. The 2006 version has the following refinements:

Dialysis dose may be quantified by any method provided that it can be related to the reference method.
Renal function may be taken into account in the dose measurement provided it is measured frequently enough to avoid overestimation as GFR falls, typically every two months.
For three times weekly dialysis, target prescribed eKt/V should be 1.2. Higher doses, up to eKt/V of 1.4 should be considered in females and patients with high co-morbidity.
For schedules other than three times weekly, dose should take frequency into account and be quoted as weekly standard Kt/V (stdKt/V), solute removal index (SRI) or equivalent renal clearance (EKR). Weekly dialysis dose should be at least equivalent to a stdKt/V or SRI of 2.1.

Rationale: Dialysis adequacy can be measured in various ways which give different results. We felt it was important to recommend reference methods to be used in guidelines. Individual facilities may use other methods, but the relationship to the reference method should be known. For three times weekly without renal function, the Gotch model is best defined in the literature. The single-pool model is subject to error due to the post-dialysis rebound which differs according to length and intensity of dialysis. Therefore, a well-validated method to correct the Gotch model for rebound effects is required to return eKt/V.

The HEMO study¹ showed no benefit in a prescribed eKt/V of 1.45 compared to the standard dose of 1.05. The mean eKt/V actually delivered (measured from pre- and post-HD blood urea) in the standard dose group was 1.16 with SD of 0.08. Under realistic conditions of routine care a prescribed target eKt/V of 1.2 would result in a similar distribution of delivered eKt/V values to the HEMO study standard dose group and at least 95% of patients would have eK/V>1.0. There is plenty of lower-grade evidence to suggest that lower doses than this are harmful. There is some evidence that higher eKt/V up to 1.4 may be beneficial in females².

EKt/V cannot account for frequency of dialysis or residual renal function. A weekly solute removal index of 2.1 removes a similar mass of urea and results in similar peak urea concentration as eKt/V of 1.2 three time a week, regardless of frequency or renal function.

References:

Eknoyan G, Beck GJ, et al. Effect of dialysis dose and membrane flux on mortality and morbidity in maintenance hemodialysis patients: Primary results of the HEMO study. N Engl J Med 347: 2010–2019, 2002.
Port FK, Wolfe RA, Hulbert-Shearon TE, McCullough KP, Ashby VB, Held J. High dialysis dose is associated with lower mortality among women but not among men. Am J Kidney Dis 2004; 43:1014-23

Prepared on behalf of the European Best Practice Guidelines Committee by James Tattersall (Sub-group Chairman)