Healthy kidneys regulate the body's internal environment of water and salts and excrete the end products of the body's metabolic activities and excess water (as urine). Dialysis is a process of removing waste products and excess fluid which build up in the body when the kidneys stop working. The word comes from the Greek 'dia' - to pass through, and 'leuin' meaning to loosen.

 Dialysys machineNormally, the human body has two kidneys, oval-shaped organs located at the back on the right and left side and partly covered by the lower ribs. In an average adult these organs are approximately four to six inches long and weigh a little over five ounces each.   

Each kidney is comprised of about one million units called nephrons, with each nephron consisting of a tube-like structure called a tubule. The closed end of the tubule forms a cup-shaped structure called a glomerular capsule, surrounding a network of tiny blood vessels called the glomerulus, which filters the blood. Filtrate drains into the tubule where its concentration is altered to form urine which flows through ureters to the bladder and is stored there until being eliminated from the body through the urethra.




Basic Principle of Dialysis

Principles of Dialysis


The kidneys daily produce a total of about 3 to 5 pints of urine consisting of waste products and excess water. Kidneys adjust the body's balance of various chemicals (sodium, potassium, calcium, phosphorous and others) and monitor the blood's acidity. Certain hormones are also produced in the kidneys. These hormones help regulate blood pressure, stimulate red blood cell production and promote strong bones.

Impaired kidney function may affect any or all of these processes and may be due to problems in the kidney, a disease in other organs, or caused by the normal, age-related processes. It may be acute or chronic and either minor or life threatening. All of these distinctions are important determinants of prognosis and appropriate treatment. When a person's loss of kidney function is so severe as to be incompatible with life, the person is said to be in renal failure--renal meaning pertaining to the kidneys.

Kidney transplantation is the preferred treatment for some persons. A successful kidney transplant can restore an individual to good health and a nearly normal lifestyle. The best results are obtained when the organ donor is a living, related donor, although good success is also achieved with cadaver kidneys. Unfortunately, while transplantation is an attractive solution in principle, there are many difficulties in its implementation, especially the severe shortage of appropriately matched donor kidneys. In addition, life-long immunosuppressive therapy, necessary to prevent rejection of the donor organ, has many deleterious effects.


Dialyser circuit


Because of these and other problems, kidney transplantation is not at present a realistic option for most patients.


Renal dialysis is an artificial method of maintaining the chemical balance of the blood when the kidneys have failed. The term dialysis refers to the process in which the components of the blood are separated using a semipermeable membrane. The blood is cleansed of impurities, either by cycling the blood through a machine, containing a membrane, and back into the patient via catheters (haemodialysis), or by cycling dialysing fluid into and out of the abdomen using the patient's peritoneal membrane as a filter (peritoneal dialysis).


DialyserHaemodialysis is a process involving pumping the blood out of a individual's body into a dialyser where impurities are removed, then returning the blood to the individual's body. Dialysers consist of three parts: a compartment for the blood, a compartment for the dialysate, and a semipermeable membrane separating the two.


Peritoneal dialysis is a process that uses the individual's peritoneum (the semipermeable membrane surrounding the abdominal organs and lining of the abdominal cavity) to perform dialysis inside the patient's body. Sterile, warmed dialysis fluid is infused via a catheter into the patient's peritoneal cavity, allowed to remain there the prescribed length of time, then drained out along with the dissolved waste products, discarded, and replaced with fresh fluid.


The effectiveness of the dialysis depends on both its duration and efficiency. Survival rates among chronic dialysis patients are related to: age at the time of starting treatments, cause of renal disease, and presence of pre-existing disease at the time of starting dialysis. In some cases, a point may be reached where dialysis appears to be of no further medical benefit, where an individual does not wish to continue, or when a surrogate decision is needed. This point may come in a matter of weeks of after many years of dialysis treatment.




Forms of Access

Haemodialysis involves the blood being taken out of the body to the machine, and then returning the blood. If you have haemodialysis, having reliable, pain-free access is extremely important.

There are two common forms of access:


AV (arterio-venous) Fistula

The access is where the needles are placed to remove blood from the body and return it to the body after it is filtered by the dialysis machine. A fistula access is created surgically by connecting an artery to a vein to strengthen the vein in the forearm, or sometimes the leg. Created surgically at least six weeks before haemodialysis begins. It is done under general anaesthetic.

Creating a fistula involves joining a vein to an artery, usually in the upper arm or wrist, to form a bigger, stronger blood vessel. This makes it easier to insert the needles that are required to withdraw blood and then return it to the body. 

Patients who have a fistula can usually feel it "buzzing" slightly. This is a good sign - it means that it's working well. If it stops buzzing, you should let your Renal Unit know, as this may be an indication that the blood has clotted.  Some people have more of a problem with clotting than others, and have difficulty keeping their fistula open. These patients may be given an artificial fistula, in which a tube is sewn in place to join the artery and vein.  Once a fistula is established, it is likely to cause few problems. In some cases, however, a fistula may be created too big or too small, and will need to be corrected. Sometimes the surgeon will have to make a graft using a vein or a piece of artificial blood vessel because it is not possible to make a fistula.



Neck Line (Haemocath)

Another form of access to the blood for dialysis is a neck line (also called a haemocath).  This is a narrow tube, which is inserted into the vein between the shoulder and the neck.  The tube is closed off when not in use, with a short length of double tube - for taking and returning blood - left outside of the skin.  With this kind of access, the patent doesn't have to wait several weeks for the vein to thicken (like you do with a fistula), so it can be used when a patient needs to start dialysis right away. It is often used on a temporary basis, until a fistula has been established.

There's no getting away from the fact that haemodialysis involves inserting needles. However, the types of needles that are put into a fistula are so thin and sharp that most patients find them to be almost painless. People who are particularly sensitive can have a local anaesthetic gel rubbed onto the skin first.  The first few times a needle is inserted into a new fistula are likely to be the most difficult, and may cause some bruising - but it really does get easier very quickly.  For people who are overwhelmed with fear (have a phobia) about needles, the prospect of dialysis may seem like a nightmare. Phobias can, however, be significantly reduced or even totally cured with the help of a trained psychologist.

The actual filtering of the blood is done by the dialyser, which is actually quite a small part of the equipment involved.  The dialyser is hooked up to a machine that performs a number of functions, including a series of automatic checks to monitor the system and make sure it is operating safely, in particular that there are no leaks of blood or air.





Adequacy : A term that refers to how well your dialysis is working. To measure adequacy, tests are carried out to see if enough fluid and waste products are being removed from your blood.

Alport's syndrome : An inherited condition that results in kidney disease. Alport's syndrome usually develops during early childhood. The condition can lead to kidney failure and to hearing and vision problems. Common symptoms include blood and protein in the urine.

APD : Stands for "automated peritoneal dialysis." APD patients use a machine at home to perform fluid exchanges. Inside the body, the peritoneal membrane acts like a filter to clean the blood.

Bladder : An organ that holds the urine excreted by the kidneys.

CAPD : Stands for "continuous ambulatory peritoneal dialysis." With CAPD, dialysis continues 24 hours a day, 7 days a week. Patients are not attached to a machine. Dialysis happens inside the body, using the peritoneal membrane as a filter.

Catheter : A slender tube inserted into a body passage or blood vessel for passing or removing fluids.

CCPD : Stands for "continuous cycling (cyclic) peritoneal dialysis." Dialysis happens inside the body, using the peritoneal membrane as a filter. A machine performs the peritoneal dialysis solution exchanges in regular cycles. Also generally known as Automated Peritoneal Dialysis (APD).

Complete kidney failure : Less than 10% of kidney function.

Congenital : Means "existing at birth."

Creatinine : Creatinine is a by-product of muscle activity.

Cycler : A machine that performs peritoneal dialysis solution exchanges in regular cycles.

Dialysate : Dialysis solution.

Dialyser : A membrane device that separates waste substances from the blood of kidney failure patients.

Dysplastic :Means "having abnormal tissue development."

Erythropoietin : A type of protein produced in the kidney. Erythropoietin stimulates red blood cell production.

ESRD : Stands for "end-stage renal disease," which means "kidney failure," which requires dialysis or kidney transplant to live.

Filtrate : liquid which has passed through a filter.

Fistula : A type of access for dialysis. The access is where the needles are placed to remove blood from the body and return it to the body after it is filtered by the dialysis machine. A fistula access is created surgically by connecting an artery to a vein to strengthen the vein in the forearm, or sometimes the leg.

Focal segmental glomerulosclerosis (FSGS) : A type of glomerulonephritis that results from scarring in parts of the glomerulus (the filter of the kidney).

Glomerulus : Blood vessels in the kidney where blood is filtered to form urine.

Glomerulonephritis : A type of nephritis (inflammation of the kidneys) that affects the glomerulus.

Graft : "To graft" means to join one thing to another; in kidney disease, usually refers to an artificial tube used to join an artery and vein for haemodialysis access or a kidney from another person in a kidney transplant.

Haemoglobin : The substance in red blood cells that carries oxygen around the body.

Peritoneal membrane : The lining of the abdomen.

Ureter : A thick-walled tube that moves the urine from the kidney to the bladder.

Urine : The kidneys filter out excess fluids and wastes, which leave the kidneys as "urine."


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