1. What is the use of haemodialysis?

The main function of haemodialysis is to remove toxins and excessive water from a patient's body. This is used in situations when a patient's kidneys stops functioning due to a variety of diseases (kidney failure) or when a patient has ingested some poisons which can be removed by the dialysis process.

2. What is the principle of haemodialysis?

Haemodialysis involves taking blood out of a patient's body and circulate it to a dialyser (an artificial kidney) which contains a semi-permeable membrane in the form of hollow fibers or flat plates. A suitable solution called dialysate is also circulated to the other side of the membrane. The toxins in the blood diffuse into the dialysate and the cleaned blood is returned to the patient. The whole process is controlled and monitored by a haemodialysis machine.

3. When will a patient need dialysis?

A kidney failure patient would need dialysis when his/her kidney function falls below 5% of normal or when his/her conditions deteriorated despite medicine and dietary treatment.

4. How can the doctor take the blood out of the body?

Creating a fistula by joining an artery to a vein at the wrist can do this. After some weeks the vein will enlarge and the doctor or the nurse can put in two needles into the vein, one needle to take the blood out and one to return the cleansed blood.

During this waiting period, if the patient needs dialysis, the doctor can insert a cannula into the big veins in the neck or beneath the clavicle for temporary dialysis.

5. Do I need blood transfusion during the dialysis?

With modern haemodialysis technique, the amount of blood loss during one dialysis treatment is negligible and no blood transfusion is required. However, if a patient is anaemic to begin with, he may need blood transfusion or the injection of erythropoietin to correct the anaemia.

6. What is erythropoietin?

Our kidneys normally produce a hormone called erythropoietin which will stimulate the bone marrow to produce red blood cells. In a kidney failure patient, the amount of erythropoietin production is reduced and the patient suffers from anaemia.

Erythropoietin can now be produced by genetic engineering technique and is now available in Hong Kong (Eprex). Giving the injection before or after the dialysis treatment can treat the anaemia.

7. How often do I need dialysis?

Since the toxin will accumulate after a dialysis treatment, a patient will need three dialyses treatment per week. However, due to financial constraints, some centres recommend a twice weekly dialysis schedule.

8. How long will each dialysis treatment last?

This depends on the size of the patient and how efficient is the dialysis which is affected by the surface area of the dialyser (artificial kidney), how fast is the blood pump working and the nature of the semi-permeable membrane inside the dialyser. The 'high-flux' dialysers are usually made of synthetic membrane and can give very efficient dialysis. As a result, a dialysis session can last from 2.5 hours to 6 hours.

9. How can the doctor determinate the duration of the dialysis session?

This can be determined by observing the patient's physical conditions and his blood chemistry before and after the dialysis. There are computer programs which can calculate the efficiency of the dialysis and give some suggestion to the duration of haemodialysis session. (urea kinetic modeling)

10. What is bicarbonate dialysis?

In 'conventional' dialysis, the dialysis solution (dialysate) contains a base called 'acetate' which will diffuse into the patient's body during the dialysis. The acetate will be converted to 'bicarbonate' in the patient's body and this will serve to maintain the acid-base balance. However, in the elderly and the weak patients, their body cannot convert the acetate into bicarbonate fast enough and there will be acetate accumulation in the body. This will give rise to low blood pressure, headache and vomiting.

Replacing the acetate with bicarbonate will relieve these symptoms, but special dialysate concentrate and special dialysis machines will be needed and hence bicarbonate dialysis is more expensive.

In some centres, bicarbonate dialysis has become the 'conventional' dialysis.

11. What is water treatment?

During each 5 hours dialysis session, about 150 litres of dialysate is needed. Since this is a very large volume, the dialysate is made by mixing water with dialysate concentrate. Raw tap water is not suitable for dialysis, it has to be treated by various process such as filtration, water softening, reverse osmosis and activate charcoal adsorption.

The dialysis water has to be free from bacterial , pyrogens and trace elements such as aluminum.

12. Is the haemodialysis treatment painful?

There will be a little bit of pain during the insertion of needles at the start of the dialysis but most patients tolerated that well. For some sensitive patients, a local anesthetic injection can be given to reduce the pain.

The rest of the haemodialysis treatment is painless. If the patient has symptoms such as chest pain, headache and low blood pressure, these can be corrected by various means such as bicarbonate dialysis, volumetric ultrafiltration control, dialysate sodium profiling and biocompatible dialyser etc.