Diffusion Kinetics in Blood during Haemodialysis and in vivo Clearance of Inorganic Phosphate

Descombes, Éric; Jutzet, André; Perriard, François; Fellay, G

doi:10.1159/000014470

Cited by 6 publications

(3 citation statements)

References 14 publications

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“…There is another technical problem in assessing dialyzer phosphate clearance that was highlighted by Descombes et al 37 They showed that when measuring dialyzer phosphate clearance in vivo, the outlet blood sample needs to be centrifuged right away, as otherwise, there is delayed entry of phosphate from RBCs into plasma, artefactually elevating the plasma concentration. This does not affect the manuscript calculations directly, but in a number of studies where clearances were calculated, this may cause marked underestimation of dialyzer phosphate clearance.…”

Section: Discussionmentioning

confidence: 99%

Comparison of modeled versus reported phosphate removal and modeled versus postdialysis serum phosphate levels in conventional hemodialysis

Daugirdas

2022

Seminars in Dialysis

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Background: We compared predictions of phosphate removal by a 2-pool kinetic model with measured phosphate removal in spent dialysate as reported by others. Methods: Twenty-six studies were identified that reported phosphate removal in 35 groups of patients. In almost all studies, patients were dialyzed for close to 4 h (range 3 to 6 h). For each study, group mean values of predialysis serum phosphate, body size, dialyzer K 0 A urea, blood and dialysate flow rates, and session lengths were input into the kinetic model. Predictions of group mean phosphate removal and postdialysis serum phosphate were compared with reported measured values. Results: Mean (by patient group) predicted phosphate removal was 931 ± 170 mg/treatment, somewhat higher (p < 0.001) than the reported measured value, 900 mg ± 287. The ratio of predicted/measured removal averaged 1.15 ± 0.427. In 5/35 patient groups (3/26 studies) the predicted/measured phosphate removal was greater than 1.50. If these groups were excluded, the mean measured phosphate removal was 990 mg versus 966 predicted, with a ratio of predicted/measured removal averaging 0.993.Measured group mean postdialysis serum phosphate values (reported in 25/35) were 2.64 ± 0.54, not significantly different from predicted (2.60 ± 0.24 mg/dl, p = NS).Conclusions: For conventional 4-h dialysis treatments, phosphate removal and postdialysis serum phosphate values predicted by a 2-pool kinetic model are similar to reported measured values.

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Section: Discussionmentioning

confidence: 99%

Comparison of modeled versus reported phosphate removal and modeled versus postdialysis serum phosphate levels in conventional hemodialysis

Daugirdas

2022

Seminars in Dialysis

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“…The mean intracellular phosphate efflux rate did not exceed 362 μmol/kg/hr. A more recent mass balance analysis showed that phosphate is only cleared from the plasma volume, and that it does not diffuse from red blood cells to plasma during the short time lapse of blood transit through the hemodialyzer [40].…”

Section: Relevance Of the Emerging Daily Dialysis Experiencementioning

confidence: 99%

The Middle Molecule Hypothesis Revisited. Should Short, Three Times Weekly Hemodialysis Be Abandoned?

Charra

Scribner

Twardowski

et al. 2002

Hemodialysis International

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When the middle molecule (MM) hypothesis was formulated in 1975, no MM had yet been identified as a uremic toxin. Meanwhile, the birth and implementation of the Kt/V concept gained wide acceptance and has remained the world standard for assessing dialysis adequacy. However, over the past 20 years, accumulating evidence has made it clear that MM's are important uremic toxins, and that the dose of dialysis based on removal of small molecular substances does not protect against excessive hemodialysis mortality, morbidity, or the presence of uremic signs and symptoms. These poor results are, in one way or another, linked to the accumulation of MM's and other substances behaving like MM's, such as phosphate. Dialysis schedules yielding the best clinical results, such as longer dialysis and more frequent dialysis, favor increased removal of middle molecular substances. The observation that short daily dialysis is giving results similar to long nocturnal quotidian dialysis supports early observations that the volume from which middle molecular substances are extracted mainly by hemodialysis is small (about as large as the extracellular volume), and that transfer of MM's from cells to extracellular fluid is very slow. This behavior of MM's is markedly different from that of small molecular substances, which are more rapidly transferred from intracellular to extracellular compartments and are more readily extracted from total body water during hemodialysis. In order to achieve even minimum adequate dialysis, it is now scientifically validated that toxic MM's must be removed in larger amounts than currently attained. This can only be accomplished by long dialysis sessions with a 3-times per week schedule or more frequent dialyses. Five hours 3 times per week represents the absolute minimum treatment. Dialy sis 6 to 7 times per week is the ideal schedule for patients who are willing to commit the time and effort in exchange for maximum well-being and long survival.

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“…Thus, on the basis of diffusion alone, phosphorus removal from an aqueous solution across a dialysis membrane should be somewhere between that of urea and creatinine. However, while urea is removed from both plasma and red blood cell water during dialysis, phosphorus, like creatinine, is removed primarily from the plasma space (7), although in one relatively recent study, some removal from red blood cells appeared to be present (8). This markedly reduces phosphorus clearance relative to urea for any level of whole blood flow rate, an effect that is magnified in patients with high levels of hematocrit (3).…”

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confidence: 99%

Removal of Phosphorus by Hemodialysis

Daugirdas

2015

Seminars in Dialysis

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The control of serum phosphorus by dialysis is made difficult by the fact that intradialytic blood levels tend to be low, and because phosphorus is removed almost exclusively from the plasma during its passage through the dialyzer. The most practical way to increase phosphorus removal is to extend dialysis time, although attention to dialysis efficiency (surface area, advanced membrane, and higher blood and dialysate flow rates) also plays a role. Benefits of hemodiafiltration in helping control serum phosphorus have been claimed, but not found in all studies. Because serum phosphorus levels tend to plateau during the later parts of a dialysis session, extending weekly dialysis time is of greater benefit for phosphorus removal than for urea removal. Increasing dialysis frequency also probably has a small benefit. It appears that 18-30 hours of dialysis per week are required to obviate the need for phosphorus binders. Several promising models of phosphorus kinetics are under development. These may help predict the change in treatment on serum phosphorus levels, but their ability to do so has not yet been critically assessed.

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Diffusion Kinetics in Blood during Haemodialysis and in vivo Clearance of Inorganic Phosphate

Cited by 6 publications

References 14 publications

Comparison of modeled versus reported phosphate removal and modeled versus postdialysis serum phosphate levels in conventional hemodialysis

Comparison of modeled versus reported phosphate removal and modeled versus postdialysis serum phosphate levels in conventional hemodialysis

The Middle Molecule Hypothesis Revisited. Should Short, Three Times Weekly Hemodialysis Be Abandoned?

Removal of Phosphorus by Hemodialysis

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