The cellular clearance theory does not explain the post-dialytic small molecule rebound

Area of Science:

• Nephrology
• Biomedical Engineering
• Pharmacology

Background:

• Maintenance hemodialysis aims to clear waste products like urea, creatinine, and phosphate.
• Accurate assessment of solute clearance is crucial for optimizing dialysis efficacy.
• Understanding factors influencing solute rebound is important for patient management.

Purpose of the Study:

• To determine normalized cellular clearance (Kcn) of urea, creatinine, and phosphate in hemodialysis patients.
• To identify factors, particularly circulatory, affecting Kcn.
• To assess if intra-dialytic blood sampling can predict post-dialytic solute rebound.

Main Methods:

• Kinetic modeling using a two-pool variable volume computer simulation.
• Analysis of 34 patients undergoing maintenance dialysis on two separate occasions.
• Determination of cellular clearance via post-dialytic rebound and mid-dialytic blood samples.
• Echocardiography and peripheral blood pressure measurements were performed.

Main Results:

• The two-pool model accurately measured urea rebound Kcn (93%) but showed lower accuracy for creatinine (49%) and phosphate (13%).
• High post-dialytic rebounds (low Kcn) correlated with erythropoietin use and end-dialytic hypotension.
• Calcium antagonist treatment was associated with significantly higher Kcn (p < 0.001).
• No correlation was found between mid-dialysis and rebound Kcn; circulatory indices did not influence Kcn.

Conclusions:

• The two-pool model is suitable for urea kinetics but not for creatinine or phosphate in hemodialysis.
• Post-dialytic solute rebound may be iatrogenic and can be mitigated by preventing hypotension and using calcium antagonists.
• Intra-dialytic blood sampling cannot reliably predict the magnitude of post-dialytic solute rebound.