Con-Current versus Counter-Current Dialysate Flow during CVVHD. A Comparative Study for Creatinine and Urea Removal

Area of Science:

• Nephrology
• Critical Care Medicine
• Biomedical Engineering

Background:

• Dialysate fluid flow relative to blood flow in dialysis circuits can impact solute clearance.
• Continuous veno-venous haemodialysis (CVVHD) is a critical care treatment, but the optimal dialysate flow direction for solute removal is not well-established.

Purpose of the Study:

• To investigate whether the direction of dialysate fluid flow (concurrent vs. counter-current) affects the removal of small solutes, specifically creatinine and urea, during CVVHD.
• To quantify the difference in solute removal efficiency based on dialysate flow direction.

Main Methods:

• A study involving 26 adult ICU patients undergoing CVVHD.
• Blood and dialysate fluid samples were collected at 1 and 4 hours under both concurrent and counter-current dialysate flow conditions.
• Urea and creatinine removal were assessed by calculating the diafiltrate/plasma concentration ratio (Uf/b and Cf/b).

Main Results:

• Counter-current dialysate flow demonstrated significantly higher mean diafiltrate/plasma concentration ratios for both creatinine and urea at both time points.
• Specifically, creatinine removal ratios were 0.87 (T1) and 0.96 (T2) for counter-current, versus 0.77 (T1) and 0.76 (T2) for concurrent flow.
• Urea removal ratios were 0.98 (T1) and 0.99 (T2) for counter-current, versus 0.81 (T1) and 0.82 (T2) for concurrent flow, indicating enhanced clearance.

Conclusions:

• Counter-current dialysate flow significantly improves the removal of small solutes like creatinine and urea during CVVHD in ICU patients.
• An approximate 20% increase in small solute removal was observed with the counter-current flow direction.
• This finding suggests optimizing dialysate flow direction in CVVHD can enhance treatment efficacy.