Previous: Introduction to dialysis
To sum up the process of hemodialysis, it involves letting the blood from the patients body flow through an artificial filter, where it is purified. This ‘purified’ blood is then returned back to patients body.
Requirements for Hemodialysis
- An access for letting blood ‘in and out’ of the body.
- A machine that will pump the blood and monitor the entire process.
- An artificial kidney ( dialyzer) that purifies blood of the toxins.
- A solution ( dialysate) that helps in the process of dialysis.
Access for Hemodialysis
The other forms of access include:
- arterio-venous Graft (AVG)
- Hemodialysis catheters
Arterio-venous Graft (AVG)
This is a synthetic tube that is placed between an artery and a vein and blood flows through it at a high velocity.
Unlike fistula, veins are not punctured. Instead, the synthetic tube is punctured to get blood flow for dialysis.
An AVG will be ready to use in two weeks time.
These catheters are usually placed in the neck veins, but sometimes, in dire emergency have to be placed in the veins of the thigh.
Catheters are the choice when there is not enough time for the AVF or AVG surgery.
The non-cuffed catheters can be used only for a few weeks after which the rates of infections and loss of blood flow increase.
The cuffed catheters are placed through a small surgery and are ready to use immediately after placement. They can stay for upto two years.
Cuffed catheters are a choice when the veins in the wrist or elbow are too thin or not suitable for an AVF surgery.
Before we go further, let us understand the circuit of hemodialysis, i.e. how the blood flows, goes through the various components and returns to the body.
The blood is taken out through AVF or AVG ( or a catheter). This blood flow is mainatained at a good velocity with the help of a blood pump in the dialysis machine.
This blood then reaches the dialyzer (see below), where there are two compartments. One compartment contains the blood and the other contains the ‘dialysate’. These compartments are separated by a semi-permeable membrane. The actual ‘cleansing’ of blood occurs here.
The clean blood is then returned to the body through a second needle in the veins or second ‘port’ of the catheter.
Once the blood comes out of the body, it has a tendency to clot. To prevent this, a drug called ‘Heparin’ is circulated through the circuit. This is done by a syringe pump located on the dialysis machine.
Pressures inside the circuit are monitored by the machine and any inadvertent air leak is trapped in the air chamber along the circuit.
Next: Dialyzer and HD machine