Prediction of postdialysis serum sodium concentration and transcellular fluid shift without measuring body fluid volumes.

The postdialysis levels of serum sodium concentration, urea concentration, and osmolality, as well as the magnitude of both transcellular fluid shifts and sodium removal, were predicted based on computer modeling without measuring body fluid volumes. A 4-h hemodialysis was performed in five patients at a constant ultrafiltration rate of 0.5 L/h using dialysate with normal (141 mEq/L) or high (150 mEq/L) Na+ concentration. The serum sodium concentration, urea concentration, and osmolality, as well as intracellular and extracellular fluid volumes, were determined before and after hemodialysis. The model predictions without measurement of body fluid volumes were in excellent agreement with measured values, suggesting clinical validity. The model may be useful in clinical practice to control the postdialysis levels of sodium and water content by computerized hemodialysis.