Text and list of links - 3 10109


Jargon buster - 0 10105


Renal (Kidney) Services


Contact: (0191) 213 7031 - Ward 31 Freeman

IntroductionShow [+]Hide [-]

What is haemodialysis?

Haemodialysis is the older of the two types of dialysis treatments available here in Newcastle. Haemo is the Greek word for blood and dialysis means a filtering process, therefore, the term haemodialysis (HD) is simply the process of filtering blood.

This treatment became available in the 1960s, and since then has enabled large numbers of kidney patients to lead almost normal lives. The main difference between haemodialysis and the other type of dialysis - called peritoneal dialysis or PD - is that in haemodialysis, the process of dialysis takes place outside the body, in a machine.

Almost all patients with end-stage renal failure (ESRF) can be treated by haemodialysis. The only real requirements are:

  • It must be possible to gain good access to a patient’s bloodstream.
  • Patients must be able to withstand major changes in blood pressure and toxin levels.

How does haemodialysis work?Show [+]Hide [-]

How does haemodialysis work?

The basic principles of dialysis apply to both haemodialysis and PD. Briefly, both types of dialysis use a special liquid (called the dialysis fluid or dialysate) and a membrane to do some of the work of the kidneys.

In haemodialysis, the process of dialysis occurs in a machine. This machine is called a dialysis or kidney machine. Blood from the patient is pumped through the machine so that dialysis can take place. Dialysis fluid and water are also pumped through the machine.

The dialysis machine contains a special filtering unit called the dialyser or artificial kidney. The dialyser is a cylinder that  contains thousands of very small hollow tubes. Each tube is made from very thin plastic, which acts as the dialysis membrane. The patient’s blood is pumped through the middle of the tubes. Meanwhile the dialysis fluid is pumped around the outside of the tubes. The process of dialysis takes place through tiny holes in the tubes. Various substances and water can easily pass through the holes, but blood cells cannot.

During dialysis, body wastes (such as creatinine and urea) pass from the blood into the dialysis fluid. Meanwhile, other substances that are needed by the body (such as bicarbonate and calcium) can be supplied to them from the dialysis fluid. This process is known as diffusion.

The second main function of dialysis, like the kidneys, is to remove water. The machine applies a sucking pressure that draws water out of the blood and into the dialysis fluid. This process is known as ultrafiltration. Instructions about the amount of water to be removed and the rate of ultrafiltration are entered into the machine at the start of each dialysis session.

How is haemodialysis given ?Show [+]Hide [-]

How is it done?

Before haemodialysis can be performed you will need a minor operation to create a fistula or insertion of a tunneled neckline (usually used as temporary measure for immediate use) as an “access” to connect you to the machine. The machine may be in a hospital renal unit, in a satellite dialysis unit or if conditions allow, the patient’s own home.

Haemodialysis is done by taking blood from the body and pumping it around a dialysis machine and through a dialyser. In the dialyser, toxins and excess water – which are equivalent to the urine produced by healthy kidneys – pass from the blood into the dialysis fluid. The cleansed blood is then returned to the body at the same rate at which it is removed. Meanwhile the “used” dialysis fluid (full of toxins and extra water) is pumped out of the dialysis machine and down the drain.

Haemodialysis is usually done three times a week , for three to five hours each session. The exact length of the sessions will depend on the amount of waste that an individual patient produces; bigger people generally need longer dialysis sessions than smaller people. Patients who do not pass any urine may also need longer sessions.

How much dialysis is needed?

In our renal unit a consultant or senior doctor and a dietitian are responsible for working out how long kidney patients need to spend on the dialysis machine, and also what size of dialyser they will use. There are different sizes of dialyser - bigger ones remove more toxins than smaller ones. Longer dialysis sessions will also remove more toxins.

As a rule, the bigger/more muscular the patient, the more dialysis they will need.  In order to change the amount of dialysis that a patient receives, the nurse can choose to alter the size of the dialyser and / or the length of time that the patient spends on the machine.

The dialysis dose can be worked out simply by comparing the levels of wastes (such as urea or creatinine) in the patient’s blood before and after dialysis and making sure that there is a significant reduction. Some units still use this method, but it is now more common to use one of the newer methods of working out dialysis doses. The first of these uses a calculation called the urea reduction ratio, the other is a method called urea kinetic modelling (UKM).  With each of these methods, dialysis target figures are the same whatever the size of the patient.

The urea reduction ratio is really just a more formal way of comparing urea levels in the blood before and after dialysis. As before, the patient’s urea levels are measured in millimoles per litre (mmol/l) of blood, but now the measurements before and after dialysis are used to calculate a percentage reduction in blood urea. (For example, if the blood urea before dialysis was 30 mmol/l, and after dialysis it was 10 mmol/l, then the percentage reduction in urea during dialysis was 50%). Such information allows adjustments to be made at future dialysis sessions in order to achieve the current urea reduction target of at least 65% per session.

Urea kinetic modelling also compares the levels of urea in the patient’s blood before and after dialysis. However, this method also takes into account the size of the dialyser (called ‘K’), the time the patient will need on the machine (called ‘t’) and a number that reflects the patient’s body weight (called ‘V’). This produces a figure called the Kt/V (pronounced ‘K.t.over V’).

Because a patient’s Kt/V figure refers to the amount of urea cleared from the body, the higher the number the better. Recent recommendations state that Kt/V should be more than 1.2 for each dialysis session.

Some patients on haemodialysis believe that it is the amount of fluid that needs to be removed which determines the length of time that they must spend on the dialysis machine. This is wrong. The most important factor affecting the length of dialysis is the amount of toxins that needs to be removed. However, if a patient has a lot of fluid to remove, they may need to spend extra time on the machine to achieve this.

More about "access"Show [+]Hide [-]

The term ‘ access’ soon becomes familiar to patients on haemodialysis, as it refers to the method by which access is gained to the blood stream so that dialysis can take place.

During haemodialysis large quantities of blood must be rapidly removed from the body and just as rapidly returned to it (at the same time). Therefore, in most cases, access has two ‘sides’. One of these (often called the ‘arterial side’) is used to take blood out of the body. The other (often called the ‘venous side’) is used to return blood to the patient after dialysis.

The types of access used depends on the individual patient and the condition of their blood vessels:

  • Arteriovenous Fistula (AVF - often just called fistula) which is formed from the patients own blood vessels. This is the preferred option, they last longer are, entirely natural and are less prone to infection than other forms of access.
  • Arteriovenous Graft (AVG) which can be either natural (taken from a different part of your body) or synthetic (from animal veins or ureter such as bovine).

Home haemodialysisShow [+]Hide [-]

In some cases it is possible to carry out haemodialysis in the patient's own home. Whether or not you are suitable for home haemodialysis will depend on your consultant’s opinion. Things that will need to be considered are:

  • That you are quite fit and do not have any access problems
  • That you are able to learn how to do haemodialysis, and be able to solve any problems that may arise during the course of the treatment.
  • That someone will be there to help every time you go on the machine

If these conditions are met and your consultant is happy to give you the okay, then it may be possible to have home training. Of course money plays an important part as your home may need well require some alterations, and a special water supply will have to be put in. Since any cost will be met by the health authority, it may not be possible to carry out alterations if they are too expensive. More often than not however, a room (or garage) conversion can be carried out.

Home Haemodialysis can be less disruptive and will reduce the amount of traveling to and from the renal unit. Obviously, one major advantage is that you can arrange to dialyse around work or other things. It does however, require a long–term commitment by both yourself and your family.

To find out more about the possibility of home treatment, speak to your Consultant who will be happy to discuss the options available to you.

© Copyright Newcastle upon Tyne Hospitals NHS Foundation Trust 2020 Site by TH_NK