Why is the dialysate continually replaced in hemodialysis?

In hemodialysis, the dialysate is continually replaced to maintain an optimal concentration gradient for the diffusion of waste products and excess electrolytes from the blood into the dialysate. This ensures efficient removal of toxins, such as urea and creatinine, and helps regulate electrolyte levels. Additionally, continuous replacement prevents the dialysate from becoming saturated with waste products, which enhances the overall effectiveness of the dialysis treatment.