Dialysis techniques

How does haemodialysis work?

Vascular approaches

Arteriovenous fistula (AVF) ?

The superficial veins do not have sufficient flow to allow haemodialysis. For this reason, the surgeon must create an arteriovenous fistula (AVF) under local anaesthetic. This involves connecting a vein to a nearby artery, so that some of the arterial blood is diverted into the vein. The vein will dilate under the effect of the blood pressure, providing sufficient blood flow for easy puncture. A vein in the forearm or upper arm is most often chosen, preferably on the "non-dominant" arm (i.e. the left arm for right-handed people and vice versa), which is less used in everyday life. The time taken for it to develop varies from a few weeks to several months. The fistula must be created early enough to ensure that it is well developed by the time dialysis is required.

Puncture may be difficult at first, but should improve within a few weeks. The pain associated with puncture is reduced or eliminated by applying a local anaesthetic to the skin (cream or self-adhesive patch) at home at the puncture site one hour before the dialysis session.
Complications may arise over time (overdevelopment, malfunction, clotting, etc.), requiring one or more surgical operations or further investigations (X-rays, ultrasound, etc.).

Precautions must be taken to ensure its longevity. The following should be avoided

Taking blood samples from the fistula or measuring blood pressure on the arm bearing the fistula.
Wearing bracelets, heavy objects or clothes that act as tourniquets.

A vascular prosthesis?

There are several types. The most common is made of goretex (PolyTetraFluoroEthylene). This is a flexible tube inserted between an artery and a vein in the forearm, upper arm or thigh. Unlike arteriovenous fistulas, it is quicker to use (2 to 3 weeks). However, it malfunctions more frequently and does not last as long. It is only used if an arteriovenous fistula is not possible. It is inserted under general anaesthetic in the operating theatre by a vascular surgeon after a surgical and anaesthetic consultation. The blood vessels may be identified beforehand using Doppler ultrasound. The preferred site is the "non-dominant" arm.

How is the arteriovenous fistula punctured?

Two punctures are needed in the fistula, using large-bore needles to facilitate blood flow:
- An arterial needle is used to aspirate the blood to be purified,
- A venous needle is used to reinject the purified blood,
These two needles are connected to the extracorporeal dialysis circuit, which in turn is connected to the dialysis generator.

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How does peritoneal dialysis work?

The peritoneal dialysis catheter is used to introduce a dialysis fluid called "dialysate" into the abdomen, in sterile plastic bags that are fitted to the tubing. The peritoneal cavity can contain up to 3 litres of dialysate. Exchanges between the dialysate and the blood eliminate waste products and excess water. Within a few hours, this dialysate is saturated. This is why the fluid in the peritoneal cavity needs to be replenished regularly.

The peritoneal approach

To use the peritoneum as a filter, a peritoneal approach must be created. To do this, a small, very flexible plastic tube called a catheter is surgically inserted into the peritoneal cavity under local or general anaesthetic. The catheter comes out partly outside the abdomen. There is no risk of it moving or falling out when you move, as it is fixed inside the abdomen. It does not hurt or interfere with movement. A tube is fitted to the end of the catheter for dialysis.

The peritoneal dialysis catheter

This is a hollow, flexible tube inserted into the abdominal cavity between the two layers of peritoneum. The catheter has a single channel that alternates the flow and return of exchange fluid. Access to the blood is provided by the vascularisation of the peritoneum. It is inserted under local or general anaesthetic by a digestive surgeon or nephrologist in the operating theatre, in compliance with strict aseptic conditions.
The risk of infection is controlled by the presence of a non-return valve at the external orifice of the catheter and under the skin by a containment system (CUFF). It must be handled with great care and asepsis. It is advisable to protect it with a sterile, watertight dressing outside dialysis periods.

The session consists of three phases:

Infusion: once the catheter tip has been connected to the bag tubing, the dialysate is introduced into your abdomen. The liquid in some bags contains sugar, which removes excess water from the body.
Stasis: the infused liquid will stagnate in the peritoneal cavity to ensure exchanges.
Drainage: after a certain period of exchange, this liquid is evacuated by gravity.

There are several ways of filling and emptying the dialysate

Manually, 4 times a day, 7 days a week or sometimes 6 days a week (continuous ambulatory peritoneal dialysis or CAPD).
It can be automated using a generator (automated peritoneal dialysis or APD). The generator, known as a "cycler", injects the liquid into the abdomen and then drains it.

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