Why is blood passed through the dialyser in many small channels instead of a large one?

Passing blood through many small channels in a dialyser, rather than a single large channel, provides several advantages in the process of haemodialysis:

Enhanced Dialysis Efficiency:

Multiple small channels allow for a larger surface area for blood-dialysate exchange. By dividing the blood flow into numerous small channels, the blood comes into close contact with the semipermeable membrane of the dialyser. This increased surface area enables more efficient removal of waste products and excess fluid from the blood.

Improved Mass Transfer:

The small channels facilitate better mass transfer between the blood and the dialysate. As blood flows through the small channels, it creates turbulent flow, which enhances the mixing of blood components and the dialysate. This turbulence promotes efficient diffusion of waste products and solutes across the membrane, resulting in improved clearance of toxins from the blood.

Prevention of Blood Clot Formation:

Large channels increase the risk of blood clot formation, also known as thrombosis, due to the slower flow of blood. The small channels in a dialyser create higher shear forces that help prevent blood from stagnating and clotting. The increased velocity and turbulence of the blood flow reduce the chances of clot formation, ensuring the safety of the haemodialysis procedure.

Optimal Use of Dialysate:

Using multiple small channels allows for a more efficient utilisation of the dialysate solution. The dialysate effectively interacts with the blood as it flows through the small channels, leading to better removal of waste products and efficient solute clearance. This optimisation helps reduce the amount of dialysate required for the haemodialysis treatment, minimising potential costs and environmental impact.

Patient Comfort:

The use of small channels contributes to patient comfort during the haemodialysis process. Multiple small channels create a lower pressure drop across the dialyser, resulting in a more gentle flow of blood. This reduced pressure reduces the risk of discomfort or pain in the patient's arm or fistula.

By incorporating multiple small channels, dialysers achieve higher dialysis efficiency, improved mass transfer, reduced clotting risk, optimal use of dialysate, and increased patient comfort. These factors collectively contribute to the effectiveness and safety of haemodialysis treatments for patients with kidney failure.