Dialysis procedures

Dialysis is a clinical procedure for removing waste and excess water from Blood when the function of Kidney is not normal and it fails to work properly.

Kidneys have an important role in maintaining the body’s internal equilibrium of water and minerals like Sodium (Na), Potassium (K), Chloride (Cl), Calcium (Ca), Phosphorus (P), Magnesium (Mg), Sulphur (S) etc. The end products of acidic metabolism which are not excreted through respiration, are excreted only through the Kidney.

The kidneys also produce certain hormones under endocrine system like Calcitriol (plays a vital role in bone formation), Renin (regulates the plasma sodium concentration and arterial blood pressure) & Erythropoietin, involved in the production of red blood cells (RBCs).

The entire dialysis procedure is a partial treatment to replace kidney function up to certain extent only because it does not perform the compromised endocrine functions of the kidney. The dialysis treatment replaces some of these functions through diffusion (waste removal) and ultra filtration (fluid removal).


The first ever Dialyzer was constructed by Willem Johan Kolff, a Dutch physician, in 1943. Later, Dr. Nils Alwall modified the similar construction by enclosing it inside a round or cylindrical container of stainless steel and this way, the first device for Hemodialysis was introduced and first patient of acute kidney failure was treated on 3rd September 1946.


Dialysis works on the principles of the diffusion (of solutes) and ultrafiltration (of fluid) through a semi-permeable membrane. Diffusion is a property of substances in which, they tend to move from an area of high concentration to an area of low concentration in water through a membrane. This is a thin layer of material that contains holes of various sizes, or pores. The smaller solutes (which is diffused in fluid) and fluid (which diffuses the solute in it) pass through the membrane, but the membrane blocks the passage of larger substances (for example, RBCs, complex proteins etc). The replication of filtering process occurs in Kidneys. When the blood enters the kidneys and the larger substances are separated from the smaller ones in the particles, called Glomerulus.

Type of Dialysis: Primary Dialysis and Secondary Dialysis

The primary dialysis may be carried out through Hemo dialysis (one of the most common procedures), Peritoneal dialysis and Hemofiltration dialysis. The secondary dialysis may be carried out through Hemodiafiltration and Intestinal dialysis.

In Hemodialysis, the wastes and excess water are removed from the blood by circulating blood outside the body through an external filter, called a Dialyzer, which contains a semi permeable membrane. During this process, a Hemodialyzer, (also called Artificial kidney), helps to filter fluids and wastes from the blood of patient. The hemodialysis treatments are normally given 3 times in a week and each procedure takes around 6-8 hours.

The dialyzer is composed of thousands of small hollow synthetic fibres. The fiber wall acts as the semi permeable membrane (referred by flux). Blood flows through the synthetic fibers and dialysis solution flows around outside of the fibers. The water and wastes move between these two solutions.

In this type of Dialysis, the blood flows in one direction and the dialysate (refers to fluids and solutes which have crossed a membrane) flows in the opposite. It is found that more Urea and creatinine is removed due to counter current flow of blood and dialysate because the concentration of solutes between the blood and dialysate is maximized. The concentration of solutes (eg: K, P and Urea) are undesirably high in the blood, but, at the same time, it is low or absent in the dialysis solution. The frequent replacement of the dialysate supports to keep the concentration of undesired solutes at lower level on this side of the membrane. The dialysis solution has normal levels of minerals like potassium and calcium which are the natural concentration in healthy blood. For another solute (bicarbonate), the dialysis solution level is kept at slightly higher level than in normal blood to catalyze the diffusion of bicarbonate into blood. It buffers the pH value, thereby neutralizing the metabolic acidosis which is often occurred in such patients. The levels of the components of dialysate must be specifically advised by a nephrologist as per the need of patient.

In Peritoneal dialysis, the waste products and water are extracted from blood inside the body using peritoneum as a natural semi-permeable membrane. The wastes and excess water move from blood, across the peritoneal membrane and into dialysis solution, called dialysate, in the abdominal cavity.

In peritoneal dialysis, a sterile solution containing glucose (called dialysate) moves through a tube into peritoneal cavity, abdominal body cavity around the intestine where the peritoneal membrane acts as a partially permeable membrane. The peritoneal membrane or peritoneum is a layer of connective tissues containing blood vessels that lines and surrounds the peritoneal, or, abdominal, cavity and abdominal organs such as stomach, spleen, liver & intestines. The waste products and excess fluid are moved by diffusion & osmosis through the peritoneum into dialysate until the dialysate reaches at the point of equilibrium with the body’s fluids. Then, the dialysate is drained and replaced with fresh dialysate. This process is repeated 4–5 times per day.

The Peritoneal dialysis is less efficient than Hemodialysis, but, because, it is carried out for a longer period of time hence, the net effect of removal of waste products and of salt and water are similar to hemodialysis. Peritoneal dialysis is carried out at home by the patient, often without help. The Peritoneal dialysis can be performed with little to no specialized equipment (other than bags of fresh dialysate).

In Hemofiltration, the blood is pumped through a dialyzer, called Hemofilter in dialysis, but, here, NO dialysate is used. A pressure gradient is applied as a result of which, the water moves across the permeable membrane rapidly, extracting many dissolved substances with it, including those with high molecular weights, which are not that much cleared by hemodialysis.

The salts and water lost from the blood during this process are replaced with another fluid, called substitution fluid. This is infused into the extracorporeal circuit during the treatment. The Hemodiafiltration is a combination of hemodialysis and hemofiltration.

In Hemodiafiltration, the blood is pumped through the blood compartment of a high flux dialyzer for high rate of ultrafiltration. During the high rate of movement of water and solutes from blood to dialysate, it must be replaced by substitution fluid which is infused directly into the blood channel. The dialysis solution also run through the dialysate compartment of the dialyzer. The combination is theoretically useful because it results in good removal of both large and small molecular weight solutes.

High Flux Dialyzer:

The dialysis done by using high flux dialyzer improves the efficiency, quality & shortening dialysis time. Such dialyzers (called artificial kidneys) have larger pores for extraction of Uremic toxins fluid. Blood Urea Nitrogen (BUN) is the measure of the toxins which kidney normally removes. However, in this process, due to large pores, the filtration of larger molecules may cause uremic symptoms which may be dangerous to dialysis patients. Such molecules (like beta 2 microglobulin) are not removed by conventional dialysis but, they are removed with high flux dialyzers. There are chances of less joint pain when switched from conventional to high flux dialysis. Thus, the removal of larger molecules may be beneficial with high flux dialysis.

The fluids are removed with much faster speed in high flux dialysis and due to fast removal, a device, called Ultra filter controller is used to regulate quantity and rate of removal of fluid to avoid dangerous drops in blood.

The disadvantage of high flux dialysis is Pyrogen reactions (high temperatures in patients) during dialysis. But, these reactions are not dangerous at all. The patient actually feels better, having less fatigue after dialysis is over. The high flux dialysis needs only minor technical adjustments in the dialyzing system.

In Intestinal dialysis, the diet is supplemented with soluble fibres such as acacia fibre which is digested by bacteria in the colon. The growth of bacteria inhances Nitrogen which is eliminated in fecal waste. Additionally, 1 to 1.5 ml of non-absorbable solutions of Polyethylene Glycol (called Mannitol) on 4 hourly basis. The Mannitol is a kind of sugar which is also used as a sweetener in diabetic food because it is poorly absorbed from the intestines.

Dialyzable substances have following properties:

Low molecular mass, High water solubility, Low protein binding capacity, Prolonged elimination (long half life), Small volume of distribution etc.

Dialyzable substances:

Ethylene Glycol, Procainamide, Methanol, Isopropyl alcohal, Barbiturates, Lithium, Bromide, Sotalol, Chloral hydrate, Ethanol, Acetone, Atenolol, Theophylline, Salicylates etc.

Pediatric dialysis:

For the last 20 years, many children have been benefited by the major improvements in both technology and clinical management of dialysis. The pain and discomfort have been reduced with the use of chronic internal jugular venous catheters and anesthetic creams for fistula puncture.

The small sized dialyzers have been designed for infants, having more biocompatible synthetic membranes and less extra-corporeal volume. Here, the length of arterial and venous tubing are made up of minimum length and diameter for pediatric patients. The pump speed is designed for lower side in accordance with the patient’s blood output capacity.

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Principle of Hemo dialysis



The hemodialysis treatment is a procedure to tackle the condition of Kidney’s failure. However, the patient may experience some of conditions as listed below:

Low blood pressure (hypotension) accompanied by shortness of breath, abdominal cramps, muscle cramps, nausea or vomiting.

Muscle cramps during hemodialysis are common symptoms which may be adjusted by fluid and sodium intake between hemodialysis treatments.

Itching during hemodialysis which is often worse during or just after the procedure.

Sleep problems are also sometimes faced by such patients because of breaks in breathing during sleep (sleep apnea) or because of aching, uncomfortable or restless legs.

Anemia due to insufficient Red Blood Cells in blood is a common complication of kidney failure and hemodialysis. The failing kidneys reduce production of a hormone called erythropoietin which stimulates formation of RBCs. Diet restrictions, poor absorption of iron, frequent blood tests, or removal of iron and vitamins by hemodialysis also can contribute to anemia.

Bone diseases may occur if the kidneys are no longer able to process vitamin D, which helps to absorb calcium. The bones may weaken. In addition, overproduction of parathyroid hormone — a common complication of kidney failure, may release calcium from bones.

High blood pressure (hypertension) due to excessive salt intake or, alcoholic drinks may lead to heart problems or strokes.

Heart failure and Pulmonary edema may occur due to excessive loss of fluids from body during hemodialysis.

Inflammation of the membrane surrounding the heart (pericarditis) may be caused due to insufficient hemodialysis.

High potassium levels (hyperkalemia) due to excessive intake of Potassium after hemodialysis must be regulated to avoid heart problems.

Dialysis-related Amyloidosis may develop due to extra deposition of Proteins on joints and tendons, causing pain, stiffness and fluid in the joints. This condition is more common if the hemodialysis continued for more than 5 years.

Depression. Changes in mood are common in people with kidney failure. If the depression or anxiety after starting hemodialysis is felt, the patient must talk with health care team about effective treatment options.

Reasons for Dialysis:

The following factors as decided by Doctor, determine the necessity of Dialysis:

Overall health, Kidney function’s signs and symptoms, Quality of life, Personal preferences etc.

The signs and symptoms of kidney failure (uremia), such as nausea, vomiting, swelling or fatigue. Your doctor uses your estimated glomerular filtration rate (eGFR) to measure your level of kidney function. The GFR is calculated using blood creatinine test results, sex, age and other factors. A normal value varies with age. This measure of kidney function can help to plan the treatment, including when to start hemodialysis.

Hemodialysis can help the body to control blood pressure and maintain the proper balance of fluid and various minerals — such as potassium and sodium — in body. Normally, hemodialysis begins well before the kidneys have shut down to the point of causing life-threatening complications.

Reasons of Kidney failure:

Diabetes, High b.p (hypertension), Nephritis, Vasculitis, Polycystic kidney disease etc.

The Kidneys may shut down suddenly (acute kidney injury) after a severe illness, complicated surgery, heart attack or other serious problem. Certain prolonged medications also may also cause kidney failure.

Hemolytic Uremic Syndrome (HUS):

It is a condition caused by the abnormal destruction of Red Blood Cells. The damaged RBCs clog the filtering system in the kidneys, causing Kidney failure.

HUS is normally developed in children after 5 to 10 days of diarrhea — often bloody — caused by infection with certain strains of Escherichia coli (E. coli) bacteria. Adults may also develop this syndrome due to E. coli bacteria, other type of infections, certain medications, or, during pregnancy. But, timely and appropriate treatment leads to a full recovery for most people, especially young children.


When is dialysis needed? It is needed when the end stage of kidney failure is developed–usually by the time about 85 to 90 % of weight is lost and Kidney have a Glomerular Filtration Rate (GFR) of less than 15. The GFR is rate of filtered fluid through the kidney. Creatinine clearance rate (CCr) is the volume of blood plasma which has cleared creatinine in per unit time and it is also an useful measure for assessing the level of GFR.

When do patients require dialysis? There are 2 major chemicals in blood, called Creatinine level and the Blood Urea Nitrogen (BUN) level. The rise in level of Creatinine and BUN in blood, indicates the decreasing ability of the kidneys to clean the body from waste products. The patients usually require dialysis when the Kidney is unable to filter waste products properly. The patient needs dialysis when the creatinine clearance is fallen as low as 10-12 cc/minute.

Can patient decide not to have dialysis treatment? Yes. The patient has the right to decide not to start dialysis. But, he/she needs to discuss the issue thoroughly with close ones and with members of the renal team.

What happens if someone stops dialysis? It seen that if a patient, having kidney failure problem, opt for dialysis or a kidney transplant, enjoys longer life and quality life ahead. However, some patients do not opt any dialysis or, kidney transplant despite having chronic kidney disease and rather they prefer taking medicinal treatment only.

Here, it is important to note for such patients that once the kidney disease reaches Stage – 5, called End Stage Renal Disease (ESRD)), many toxins are built up in body and death usually comes within a few weeks.