Dialysis – Indications, Contraindications

Dialysis is the process of removing excess water, solutes, and toxins from the blood in people whose kidneys can no longer perform these functions naturally. This is referred to as renal replacement therapy.

Dialysis is used in patients with rapidly developing loss of kidney function, called acute kidney injury (previously called acute renal failure), or slowly worsening kidney function, called Stage 5 chronic kidney disease (previously called chronic kidney failure, end-stage renal disease, and end-stage kidney disease).

Dialysis is used as a temporary measure in either acute kidney injury or in those awaiting kidney transplant and as a permanent measure in those for whom a transplant is not indicated or not possible.[rx]


There are several signs of glomerular dysfunction that can be used in the diagnosis and are also used to separate diseases into nephrotic or nephritic syndromes.

  • Protein in the urine (proteinuria) – This is a hallmark measure of renal disease, and the primary measure used to differentiate between nephrotic and nephritic syndromes. Protein in the urine can be due to glomerular disease-causing proteins to leak into the urine, or a defect in protein reabsorption in the kidney tubules. Proteinuria may cause foamy urine.  Generally, very high protein concentration in the urine or “nephrotic range” > 200 mg/l is associated with podocyte disruption, which results in non-selective protein loss. Losses of protein into the urine is typically associated with reduced proteins or albumin in the blood (proteinemia or hypoalbuminemia).
  • Blood in the urine (hematuria) – The presence of hemoglobin from leaked red blood cells gives the urine a pink or light brown (cola-colored). This presentation is a typical symptom of nephrotic syndrome, along with lower proteinuria, and is proteinuria is associated with nephritic attributable to a defect in the glomerular basement membrane.
  • Edema – Protein losses from the blood results in a reduction of colloid oncotic pressure and increased filtration from the capillaries resulting in the excess, non-resorbed fluid accumulation within the intercellular spaces to cause swelling. This swelling due to edema is usually more noticeable in the hands, ankles, or periorbital.
  • Uremia – reduced glomerular filtration rate: Disruption of the barrier can also result in reduced filtration and thus the accumulation of waste products such as. Creatinine and urea nitrogen in the blood.

Acidosis: This is beyond a discussion of the glomerulus, but still bears mentioning. Kidney tubules are involved in the metabolic acid-base homeostatic regulation of blood pH.


Dialysis works on the principles of the diffusion of solutes and the ultrafiltration of fluid across a semi-permeable membrane. Diffusion is a property of substances in water; substances in water tend to move from an area of high concentration to an area of low concentration.[rx] Blood flows by one side of a semi-permeable membrane, and a dialysate, or special dialysis fluid, flows by the opposite side. A semipermeable membrane is a thin layer of material that contains holes of various sizes, or pores. Smaller solutes and fluid pass through the membrane, but the membrane blocks the passage of larger substances (for example, red blood cells and large proteins). This replicates the filtering process that takes place in the kidneys when the blood enters the kidneys and the larger substances are separated from the smaller ones in the glomerulus.[rx]

Osmosis diffusion ultrafiltration and dialysis

The two main types of dialysis, hemodialysis and peritoneal dialysis, remove wastes and excess water from the blood in different ways.[rx] Hemodialysis removes wastes and water by circulating blood outside the body through an external filter, called a dialyzer, that contains a semipermeable membrane. The blood flows in one direction and the dialysate flows in the opposite. The counter-current flow of the blood and dialysate maximizes the concentration gradient of solutes between the blood and dialysate, which helps to remove more urea and creatinine from the blood. The concentrations of solutes normally found in the urine (for example potassium, phosphorus, and urea) are undesirably high in the blood, but low or absent in the dialysis solution, and constant replacement of the dialysate ensures that the concentration of undesired solutes is kept low on this side of the membrane. The dialysis solution has levels of minerals like potassium and calcium that are similar to their natural concentration in healthy blood. For another solute, bicarbonate, dialysis solution level is set at a slightly higher level than in normal blood, to encourage the diffusion of bicarbonate into the blood, to act as a pH buffer to neutralize the metabolic acidosis that is often present in these patients. The levels of the components of dialysate are typically prescribed by a nephrologist according to the needs of the individual patient.

In peritoneal dialysis, wastes and water are removed from the blood inside the body using the peritoneum as a natural semipermeable membrane. Wastes and excess water move from the blood, across the peritoneal membrane and into a special dialysis solution, called dialysate, in the abdominal cavity.


There are three primary and two secondary types of dialysis: hemodialysis (primary), peritoneal dialysis (primary), hemofiltration (primary), hemodiafiltration (secondary) and intestinal dialysis (secondary).


In hemodialysis, the patient’s blood is pumped through the blood compartment of a dialyzer, exposing it to a partially permeable membrane. The dialyzer is composed of thousands of tiny hollow synthetic fibers. The fiber wall acts as the semipermeable membrane. Blood flows through the fibers, dialysis solution flows around the outside of the fibers, and water and wastes move between these two solutions.[rx] The cleansed blood is then returned via the circuit back to the body. Ultrafiltration occurs by increasing the hydrostatic pressure across the dialyzer membrane This usually is done by applying negative pressure to the dialysate compartment of the dialyzer. This pressure gradient causes water and dissolved solutes to move from blood to dialysate and allows the removal of several liters of excess fluid during a typical 4-hour treatment. In the United States, hemodialysis treatments are typically given in a dialysis center three times per week (due in the United States to Medicare reimbursement rules); however, as of 2005 over 2,500 people in the United States are dialyzing at home more frequently for various treatment lengths.[rx] Studies have demonstrated the clinical benefits of dialyzing 5 to 7 times a week, for 6 to 8 hours. This type of hemodialysis is usually called nocturnal daily hemodialysis, which a study has shown it provides a significant improvement in both small and large molecular weight clearance and decreases the need for phosphate binders.[rx] These frequent long treatments are often done at home while sleeping, but home dialysis is a flexible modality and schedules can be changed day to day, week to week. In general, studies show that both increased treatment length and frequency are clinically beneficial.[rx]

To get the blood to flow to the artificial kidney, your doctor will perform surgery to create an entrance point (vascular access) into your blood vessels. The three types of entrance points are:

  • Arteriovenous (AV) fistula. This type connects an artery and a vein. It’s the preferred option.
  • AV graft. This type is a looped tube.
  • Vascular access catheter. This may be inserted into the large vein in your neck.

Both the AV fistula and AV graft are designed for long-term dialysis treatments. People who receive AV fistulas are healed and ready to begin hemodialysis two to three months after their surgery. People who receive AV grafts are ready in two to three weeks. Catheters are designed for short-term or temporary use.

Peritoneal dialysis

There are numerous different types of peritoneal dialysis. The main ones are:

  • Continuous ambulatory peritoneal dialysis (CAPD). In CAPD, your abdomen is filled and drained multiple times each day. This method doesn’t require a machine and must be performed while awake.
  • Continuous cycling peritoneal dialysis (CCPD). CCPD uses a machine to cycle the fluid in and out of your abdomen. It’s usually done at night while you sleep.
  • Intermittent peritoneal dialysis (IPD). This treatment is usually performed in the hospital, though it may be performed at home. It uses the same machine as CCPD, but the process takes longer.

In peritoneal dialysis, a sterile solution containing glucose (called dialysate) is run through a tube into the peritoneal cavity, the abdominal body cavity around the intestine, where the peritoneal membrane acts as a partially permeable membrane.

This exchange is repeated 4–5 times per day; automatic systems can run more frequent exchange cycles overnight. Peritoneal dialysis is less efficient than hemodialysis, but because it is carried out for a longer period of time the net effect in terms 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. This frees patients from the routine of having to go to a dialysis clinic on a fixed schedule multiple times per week. Peritoneal dialysis can be performed with little to no specialized equipment (other than bags of fresh dialysate).


Continuous venovenous haemofiltration with pre- and post-dilution (CVVH)

Hemofiltration is a similar treatment to hemodialysis, but it makes use of a different principle. The blood is pumped through a dialyzer or “hemofilter” as in dialysis, but no dialysate is used. A pressure gradient is applied; as a result, water moves across the very permeable membrane rapidly, “dragging” along with it many dissolved substances, including ones with large molecular weights, which are not cleared as well by hemodialysis. Salts and water lost from the blood during this process are replaced with a “substitution fluid” that is infused into the extracorporeal circuit during the treatment.


Hemodiafiltration is a combination of hemodialysis and hemofiltration, thus used to purify the blood from toxins when the kidney is not working normally and also used to treat acute kidney injury (AKI).

Intestinal dialysis

Continuous venovenous haemodiafiltration (CVVHDF)

In intestinal dialysis, the diet is supplemented with soluble fibers such as acacia fiber, which is digested by bacteria in the colon. This bacterial growth increases the amount of nitrogen that is eliminated in fecal waste.[rx][rx][rx] An alternative approach utilizes the ingestion of 1 to 1.5 liters of non-absorbable solutions of polyethylene glycol or mannitol every fourth hour.[rx]


The decision to initiate dialysis or hemofiltration in patients with kidney failure depends on several factors. These can be divided into acute or chronic indications.

Depression and kidney failure symptoms can be similar to each other. It’s important that there’s open communication in a dialysis team and the patient. Open communication will allow us to give a better quality of life. Knowing the patients’ needs will allow the dialysis team to provide more options like changes in dialysis type like home dialysis for patients to be able to be more active or changes in eating habits to avoid unnecessary waste products.

Acute indications

Indications for dialysis in a patient with acute kidney injury are summarized with the vowel mnemonic of “AEIOU”:[rx]

  • Acidemia from metabolic acidosis in situations in which correction with sodium bicarbonate is impractical or may result in fluid overload.
  • Electrolyte abnormality, such as severe hyperkalemia, especially when combined with AKI.
  • Intoxication, that is, acute poisoning with a dialyzable substance. These substances can be represented by the mnemonic SLIME: salicylic acid, lithium, isopropanol, magnesium-containing laxatives and ethylene glycol.
  • Overload of fluid not expected to respond to treatment with diuretics
  • Uremia complications, such as pericarditis, encephalopathy, or gastrointestinal bleeding.

Chronic indications

Chronic dialysis may be indicated when a patient has symptomatic kidney failure and low glomerular filtration rate (GFR < 15 mL/min).[rx] Between 1996 and 2008, there was a trend to initiate dialysis at progressively higher estimated GFR, eGFR. A review of the evidence shows no benefit or potential harm with early dialysis initiation, which has been defined by start of dialysis at an estimated GFR of greater than 10ml/min/1.73. Observational data from large registries of dialysis patients suggests that early start of dialysis may be harmful.[rx] The most recent published guidelines from Canada, for when to initiate dialysis, recommend an intent to defer dialysis until a patient has definite kidney failure symptoms, which may occur at an estimated GFR of 5-9ml/min/1.732.[rx]

There are 2 main types of dialysis: hemodialysis and peritoneal dialysis.

  • hemodialysis involves diverting blood into an external machine, where it’s filtered before being returned to the body
  • peritoneal dialysis involves pumping dialysis fluid into the space inside your abdomen (tummy) to draw out waste products from the blood passing through vessels lining the inside of the abdomen


Preparing for treatment

Before hemodialysis can start, you’ll usually need to have a blood vessel called an arteriovenous fistula (AV fistula) created in your arm. This blood vessel is created by connecting an artery to a vein.

Joining a vein and an artery together makes the blood vessel larger and stronger. This makes it easier to transfer your blood into the dialysis machine and back again.

The operation to create the AV fistula is usually carried out around 4 to 8 weeks before hemodialysis begins. This allows the tissue and skin surrounding the fistula to heal.

If your blood vessels are too narrow to create an AV fistula, an alternative procedure known as an AV graft may be recommended. A piece of synthetic tubing is used to connect the artery to the vein.

As a short-term measure, or in an emergency, you may be given a neckline. This is where a small tube is inserted into a vein in your neck.

The hemodialysis process

Most people need 3 sessions of hemodialysis a week, with each session lasting around 4 hours. This can be done in a hospital or at home.

2 thin needles will be inserted into your AV fistula or graft and taped into place. One needle will slowly remove the blood and transfer it to a machine called a dialyzer or dialysis machine.

The dialysis machine is made up of a series of membranes that act as filters and a special liquid called dialysate.

The membranes filter waste products from your blood, which are passed into the dialysate fluid.

The used dialysate fluid is pumped out of the dialyzer, and the filtered blood is passed back into your body through the second needle.

During your dialysis sessions, you’ll sit or lie on a couch, recliner or bed. You’ll be able to read, listen to music, use your mobile phone or sleep.

Haemodialysis is not painful, but some people feel a bit sick and dizzy and may have muscle cramps during the procedure.

This is caused by the rapid changes in blood fluid levels that occur during the treatment.

After the dialysis session, the needles are removed and a plaster is applied to prevent bleeding.

If you were treated in the hospital, you can usually go home shortly afterward.

Fluid and diet restrictions

If you’re having hemodialysis, the amount of fluid you can drink will be severely restricted.

This is because the dialysis machine will not be able to remove 2 to 3 days’ worth of excess fluid from your blood in 4 hours if you drink too much.

This can lead to serious problems where excess fluid builds up in your blood, tissues and lungs.

The amount of fluid you’re allowed to drink will depend on your size and weight. Most people are only allowed to drink 1,000 to 1,500ml (2 to 3 pints) of fluid a day.

You’ll also need to be careful what you eat while having haemodialysis.

This is because minerals such as sodium (salt), potassium and phosphorus, which would normally be filtered out by your kidneys, can build up to dangerous levels quickly between treatment sessions.

You’ll be referred to a dietitian so a suitable diet plan can be drawn up for you.

Diet plans differ from person to person, but it’s likely you’ll be advised to avoid eating foods high in potassium and phosphorus, and cut down the amount of salt you eat.

Peritoneal dialysis

There are 2 main types of peritoneal dialysis:

  • continuous ambulatory peritoneal dialysis (CAPD) – where your blood is filtered several times during the day
  • automated peritoneal dialysis (APD) – where a machine helps filter your blood during the night as you sleep

Both treatments can be done at home once you have been trained to carry them out yourself.

They’re described in more detail below.

Preparing for treatment

Before you can have CAPD or APD, an opening will need to be made in your abdomen.

This will allow the dialysis fluid (dialysate) to be pumped into the space inside your abdomen (the peritoneal cavity).

A cut (incision) is usually made just below your belly button. A thin tube called a catheter is inserted into the incision and the opening will normally be left to heal for a few weeks before treatment starts.

The catheter is permanently attached to your abdomen, which some people find difficult.

If you’re unable to get used to the catheter, you can have it removed and switch to haemodialysis instead.

Continuous ambulatory peritoneal dialysis

The equipment used to carry out CAPD consists of:

  • a bag containing dialysate fluid
  • an empty bag used to collect waste products
  • a series of tubing and clips used to secure both bags to the catheter
  • a wheeled stand that you can hang the bags from

At first, the bag containing dialysate fluid is attached to the catheter in your abdomen.

This allows the fluid to flow into the peritoneal cavity, where it’s left for a few hours.

While the dialysate fluid is in the peritoneal cavity, waste products and excess fluid in the blood passing through the lining of the cavity are drawn out of the blood and into the fluid.

A few hours later, the old fluid is drained into the waste bag. New fluid from a fresh bag is then passed into your peritoneal cavity to replace it and is left there until the next session.

This process of exchanging the fluids is painless and usually takes about 30 to 40 minutes to complete.

Exchanging the fluids is not painful, but you may find the sensation of filling your abdomen with fluid uncomfortable or strange at first. This should start to become less noticeable as you get used to it.

Most people who use CAPD need to repeat this around 4 times a day. Between treatment sessions, the bags are disconnected and the end of the catheter is sealed.

Automated peritoneal dialysis (APD)

Automated peritoneal dialysis (APD) is similar to CAPD, except a machine is used to control the exchange of fluid while you sleep.

You attach a bag filled with dialysate fluid to the APD machine before you go to bed. As you sleep, the machine automatically performs a number of fluid exchanges.

You’ll usually need to be attached to the APD machine for 8 to 10 hours.

At the end of the treatment session, some dialysate fluid will be left in your abdomen. This will be drained during your next session.

During the night, an exchange can be temporarily interrupted if, for example, you need to get up to go to the toilet.

Some people who have APD worry that a power cut or other technical problem could be dangerous.

But it’s usually safe to miss 1 night’s worth of exchanges as long as you resume treatment within 24 hours.

You’ll be given the telephone number of a 24-hour hotline you can call if you experience any technical problems.

Fluid and diet restrictions

If you’re having peritoneal dialysis, there are generally fewer restrictions on diet and fluid intake compared with haemodialysis because the treatment is carried out more often.

But you may sometimes be advised to limit how much fluid you drink, and you may need to make some changes to your diet. A dietitian will discuss this with you if appropriate.

Dialysis and pregnancy

Becoming pregnant while on dialysis can sometimes be dangerous for the mother and baby.

It’s possible to have a successful pregnancy while on dialysis, but you’ll probably need to be monitored more closely at a dialysis unit and may need more frequent or longer treatment sessions.

If you’re considering trying for a baby, it’s a good idea to discuss this with your doctor first.

Dialysis equipment

If you’re having home hemodialysis or peritoneal dialysis, the supplies and equipment you need will normally be provided by your hospital or dialysis clinic.

You’ll be told how to get and store your supplies as part of your training in carrying out the procedure.

It’s important to make sure you have enough supplies of equipment in case of an emergency, such as adverse weather conditions that prevent you from obtaining supplies.

Your doctor or nurse may suggest keeping at least a week’s worth of equipment as an emergency backup supply.

You should also let your electrical company know if you’re using home hemodialysis or automated peritoneal dialysis.

This is so they can treat you as a priority in the event that your electrical supply is disrupted.


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