A simulation study on transcellular fluid shifts induced by hemodialysis

Abstract

A computer-based model has been developed to predict the changes in serum sodium, urea concentration, and osmolality as well as transcellular fluid distribution which occur during hemodialysis. Sodium and urea transfers across the dialyzer membrane and transcellular fluid shifts in response to the sodium transfer were modeled assuming that only sodium and its accompanying anions are important as effective osmotic substances in extracellular fluid. Model predictions were consistent with values measured in five patients who were studied on hemodialysis at three different dialysate sodium concentrations equal to 7% below and 7% above the predialysis serum concentration. The measurements and model predictions indicate that serum sodium concentration decreases and intracellular fluid volume increases in dialyses with dialysate Na+ concentration used in conventional hemodialysis, whereas serum sodium concentration increases and intracellular volume decreases in high sodium dialyses. An analysis of model predictions indicates that a reasonable estimation of total body water and the intracellular to extracellular volume ratio enables us to accurately predict the magnitude of transcellular fluid shifts induced by hemodialysis as well as the postdialysis serum sodium concentration and osmolality.

Increase in Blood Volume during Dialysis without Ultrafiltration

“…This finding is contrary to predictions derived from mathematical modeling in which RBV is predicted to decrease [6][7][8]. Diffusive dialysis leads to a decreased extracellular osmolarity, as there is an efflux of urea from the extracellular space.…”

“…This could suggest that the hemodynamic instability that occurs during dialysis results from changes in osmolality [3][4][5]. Using kinetic modelling, the rapid fall in the urea concentration of the extracellular compartment is predicted to induce a volume shift from the extracellular to the intracellular compartment [6][7][8]. On the other hand, some studies failed to observe differences in plasma volume preservation between ultrafiltration and ultrafiltration combined with hemodialysis [9][10][11].…”

Validation of a Simple Method for Assessing Sodium Intake in Dialysis Patients

“…Experimental studies by means of volume expansion with hypertonic and hypotonic saline solutions have provided evidence that sodium is functionally distributed in a volume equal to that of TBW [9][10][11]. Furthermore, previous studies have also shown that the product of serum sodium concentration and the intracellular fluid volume is constant in dialysis patients [2][3][4][5][6][7][8][9][10][11][12].…”

“…During dialysis, instead, water and sodium removal are closely interrelated since with each liter of ultrafiltrate a fixed quantity of sodium is lost, almost equal to the cation content in the ultrafiltrated plasma. For this reason the sodium concentration of the dialysis fluid plays a key role in adjusting the sodium balance through the diffusive transport from the dialysate to the patient or, more rarely, from the patient to the dialysate [2].…”

Sodium Gradient: A Tool to Individualize Dialysate Sodium Prescription in Chronic Hemodialysis Patients?

“…Gibbs-Donnan effect) [1,6]. In general, these opposing effects tend to cancel out [22]. Finally, the preparation of the dialysate may lack precision and dialysis machines may not be adequately calibrated.…”