Hemodialysis Ultrafiltration Rate Targets Should Be Scaled to Body Surface Area Rather than to Body Weight

Abstract

The association between higher ultrafiltration rates and poor outcomes in hemodialysis patients has received increased attention, to the point that various regulatory entities are considering adding ultrafiltration rate as a quality measure to be monitored and controlled. Most of the discussion to date has focused on ultrafiltration rate scaled to body weight, or more correctly, body mass (ml/hour per kg). One outcome study suggests that ultrafiltration rate might best be not scaled at all to body size, as modestly higher ultrafiltration rate in very small-size patients may be associated with some survival benefit, probably via increased dietary intake. Outcomes studies also suggest that the risk of exceeding a weight-scaled ultrafiltration target may be magnified in very large patients, and that body weight-scaled ultrafiltration targets in such patients should be set a lower level. Here, we present an analysis, based on physiological hemodynamic arguments, that it would be better to scale ultrafiltration rate to body surface area rather than to body mass. Whatever ultrafiltration rate is scaled to, attempts to restrict ultrafiltration rate by limiting interdialytic weight gain in small, possibly malnourished patients, should be done cautiously, to prevent an inadvertent lowering of intake of calories and dietary protein.

Association between Ultrafiltration Rate and Clinical Outcome Is Modified by Muscle Mass in Hemodialysis Patients

“…In the present study, we calculated UFR normalized to body weight. It may be not suitable for very small-or largesized patients to normalize UFR to body mass [32]. However, the median (IQR) of body weight in our cohort was 58 (50-68) kg, relatively moderate weight.…”

Ultrafiltration Rate Scaling in Hemodialysis Patients

“…10 In their editorial, Daugirdas and Schneditz suggested that it may be more appropriate to scale UF rates to body surface area rather than to body weight. Relying on data from the Hemodialysis (HEMO) Study, the authors proposed that body surface area might better reflect vascular refilling capacity than body weight.…”

“…They hypothesized that body surface area’s correlation with both blood volume and extracellular volume render it more relevant to refilling capacity than body weight on its own. 10 Then, citing data from an observational analysis of UF rates (considered scaled to body weight, body mass index and body surface area) and all-cause mortality by Assimon et al , they noted that: 1) the rapid UF rate—mortality association may be more pronounced in patients of greater body weight, and 2) the UF rate—mortality association may be more consistent when scaled to body surface area than when scaled to body weight. 4 Daugirdas and Schneditz appropriately pointed out that the Assimon et al .…”

“…analyses were not stratified by sex, potentially obscuring important information that could shed light on the optimal approach to UF rate scaling. 10 …”

Pediatric intradialytic hypotension: recommendations from the Pediatric Continuous Renal Replacement Therapy (PCRRT) Workgroup

“…Previous studies have discussed UF rates adjusted to body mass/weight. Daugirdas et al found it advantageous to adjust UF rates to body surface area rather than body mass [37]. Due to the lack of clinical studies testing the efficacy of body surface area based UF rate adjustments in children, the consensus panel recommended against the usage of this method (Table 4).…”