Cochin Cardiac Club

Health Blog by Dr.Uday Nair


What is dialysis?

The kidneys are responsible for filtering waste products from the blood. Dialysis is a procedure that is a substitute for many of the normal duties of the kidneys. The kidneys are two organs located on either side of the back of the abdominal cavity. Dialysis can allow individuals to live productive and useful lives, even though their kidneys no longer work adequately.

Dialysis helps the body by performing the functions of failed kidneys. The kidney has many roles. An essential job of the kidney is to regulate the body's fluid balance. It does this by adjusting the amount of urine that is excreted on a daily basis. On hot days, the body sweats more. Thus, less water needs to be excreted through the kidneys. On cold days, the body sweats less. Thus, urine output needs to be greater in order to maintain the proper balance within the body. It is the kidney's job to regulate fluid balance by adjusting urine output.

Another major duty of the kidney is to remove the waste products that the body produces throughout the day. As the body functions, the cells use energy. The operation of the cells produces waste products that must be removed from the body. When these waste products are not removed adequately, they build up in the body. An elevation of waste products, as measured in the blood, is called "azotemia." When waste products accumulate they, cause a sick feeling throughout the body called "uremia."

When do patients require dialysis?

Patients usually require dialysis when the waste products in their body become so high that they start to become sick from them. The level of the waste products usually builds up slowly. Doctors measure several blood chemical levels to help decide when dialysis is necessary. The two major blood chemical levels that are measured are the "creatinine level" and the "blood urea nitrogen" (BUN) level. As these two levels rise, they are indicators of the decreasing ability of the kidneys to cleanse the body of waste products.
Doctors use a urine test, the "creatinine clearance," to measure the level of kidney function. The patient saves urine in a special container for one full day. The waste products in the urine and in the blood are estimated by measuring the creatinine. By comparing the blood and urine level of this substance, the doctor has an accurate idea of how well the kidneys are working. This result is called the creatinine clearance. Usually, when the creatinine clearance falls to 10-12 cc/minute, the patient needs dialysis.
The doctor uses other indicators of the patient's status to decide about the need for dialysis. If the patient is experiencing a major inability to rid the body of excess water, or is complaining of problems with the heart, lungs, or stomach, or difficulties with taste or sensation in their legs, dialysis may be indicated even though the creatinine clearance has not fallen to the 10-12 cc/minute level.

What are the different types of dialysis?

Dialysis can be performed using several different methods.


Peritoneal dialysis filters waste using the peritoneal membrane inside the abdomen. The abdomen is filled with special solutions that help remove toxins. The solutions remain in the abdomen for a time and then are drained out. This form of dialysis can be performed at home, but must be done every day.


Hemodialysis works by circulating the blood through special filters outside the body. The blood flows across a filter, along with solutions that help remove toxins.
Dialysis uses special ways of accessing the blood in the blood vessels. The access can be temporary or permanent.
Temporary access takes the form of dialysis catheters -- hollow tubes placed in large veins that can support acceptable blood flows. Most catheters are used in emergency situations for short periods of time. However, catheters called tunneled catheters can be used for prolonged periods of time, often weeks to months.
Permanent access is created by surgically joining an artery to a vein. This allows the vein to receive blood at high pressure, leading to a thickening of the vein's wall. This vein can handle repeated puncture and also provides excellent blood flow rates.
The connection between an artery and a vein can be made using blood vessels (an arteriovenous fistula, or AVF) or a synthetic bridge (arteriovenous graft, or AVG). Your health care provider may suggest an AVF, because it has lower infection rates and better long-term function than an AVG.
Blood is diverted from the access point in the body to a dialysis machine. Here, the blood flows counter-current to a special solution called the dialysate. The chemical imbalances and impurities of the blood are corrected and the blood is then returned to the body. Typically, most patients undergo hemodialysis for three sessions every week. Each session lasts 3 - 4 hours.

How to prepare for the test:

When possible, patients should prepare for dialysis before dialysis is absolutely necessary.
It is important to stick to the diet and medicines prescribed by the dialysis staff and your kidney specialist (nephrologist).
The doctor will make the following assessments before beginning the hemodialysis procedure:
  • Blood pressure
  • Breathing rate
  • Chest assessment
  • Examination of vein access
  • Heart rate
  • Temperature
  • Weight

How the test will feel:

Because dialysis takes several hours, it may be tedious. With children, it is especially important to have games, something to read, or other distractions.

Why the test is performed:

The kidneys function as filters for the blood, removing waste products. They also:
  • Regulate body water
  • Maintain electrolyte balance
  • Ensure that the blood pH remains between 7.35 and 7.45
Dialysis replaces some of the functions for kidneys that aren't working properly. It removes contaminants from the blood that could, and eventually would, lead to death if the kidney is not functioning.
Since dialysis is not a constant process, it cannot monitor body functions as do normal kidneys, but it can eliminate waste products and restore electrolyte and pH levels on an as-needed basis.
Dialysis is most often used for patients who have kidney failure, but it can also quickly remove drugs or poisons in acute situations. This technique can be lifesaving in people with acute or chronic kidney failure.

What are the advantages of the different types of dialysis?

Each of the two types of dialysis, hemodialysis and peritoneal dialysis, has advantages and disadvantages. It is up to the patient to decide which of these procedures is best by considering her/his life style, other medical conditions, support systems, and how much responsibility and participation in the treatment program he/she desires. Each patient must view the two types of dialysis procedures from her/his own perspective.
Regardless of which type of dialysis is chosen , patients have certain responsibilities such as following a diet program, watching their fluid intake and taking special vitamins and other medicines to control blood pressure and calcium and phosphorus balance.
For many patients, the major advantage of hemodialysis is minimal participation in the treatment. However, patients are required to adhere to a specific schedule and travel to the dialysis unit. Hemodialysis also requires stricter diet control and fluid control than peritoneal dialysis.
For those patients preferring more independence, peritoneal dialysis allows for more flexible scheduling and can be performed at home. The patient still must undergo a certain amount of dialysis each day, but can alter the exact timing of the dialysis procedure. On the other hand, peritoneal dialysis must be done every day of the week.
The major problem with peritoneal dialysis is infection. The patient has a plastic tube that goes from the peritoneal cavity to the outside of the body and this is a potential site for the entry of bacteria into the body. Great emphasis is placed on cleanliness and technique during the training sessions.

Dialysis At A Glance
  • Dialysis is a procedure that is a substitute for many of the normal duties of the kidneys.
  • Dialysis allows patients with kidney failure a chance to live productive lives.
  • There are two types of dialysis: hemodialysis and peritoneal dialysis.
  • Each type of dialysis has advantages and disadvantages. Patients can often choose the type of long term dialysis that best matches their needs

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