Medical dialysis

Dialysis is a principle of blood purification. It is a method of exchange between two solutions, blood and a liquid called “dialysate”, through a semipermeable membrane.

This membrane has multiple holes or pores allowing the passage of water molecules and low molecular weight solutes (high molecular weight solutes like plasma proteins cannot pass through this membrane).

Mechanisms involved in dialysis


The transfer of solutes by diffusion through the dialysis membrane results from a movement of the molecules contained in the solution. If the molecule encounters a pore the size of which corresponds to its own, it will cross the membrane.

The “concentration gradient” of the solute on either side of the membrane is the main determinant of the diffusion of the molecules: the higher the solution, the more the molecules cross the membrane towards the solution whose solute concentration is the lowest.

Low molecular weight waste (urea, creatinine, potassium, etc.) which accumulates in the patient’s blood between two sessions, is eliminated with the dialysate at the end of the session. The transfer of solutes from the blood to the dialysate is rapid, the calcium concentration in the dialysate being higher than that of ionized calcium in the blood, the session allows a transfer of calcium to the patient’s blood (calcium bound to proteins does not broadcast). The same is true for baking soda.

Ultra filtration

This is the transfer of water molecules across the membrane under the effect of pressure hydrostatic (in the case of hemodialysis) or osmotic (in the case of dialysis
peritoneal). This technique removes accumulated water (constituting a hydrosodified filler) by the oliguric or anuric patient between two dialyses.

Control of the acid-base balance

In the absence of kidney function, non-volatile acids from food processing are not eliminated. The accumulation of acids must therefore be “buffered” by bicarbonates transferred into the patient’s blood during the session.

Periodic hemodialysis

  it is the most used method, it concerns more than 90% It is a mode of ERA which aims to restore the balance of the interior environment through a discontinuous treatment of three to six hours per session, in two to three sessions per week.

It is carried out thanks to an extra-corporeal circuit of blood and dialysate, the dialysis liquid being produced by a machine called dialysis generator.

Peritoneal dialysis

Peritoneal dialysis is more particularly indicated in young adults awaiting a kidney transplant and concerns more than 5% of patients. This method involves the injection of a dialysate into the abdominal cavity using a surgically implanted catheter. The exchange of solutes takes place through the peritoneal membrane. The dialysate, once saturated with urea, creatinine and other molecules, is eliminated.

These manipulations are renewed manually on average four times a day (continuous ambulatory peritoneal dialysis or CAPD) or carried out by an automated device called a “cycler”, the treatment then taking place overnight (automated peritoneal dialysis or APD). Peritoneal dialysis is performed at home either by the patient himself, by a relative or by a private nursing practice after a period of learning.