Dialysis substitutes the natural work of the kidneys, so it is also known as renal replacement therapy (RRT).
Healthy kidneys regulate the body's levels of water and minerals and remove waste. The kidneys also secrete certain products that are important in metabolism, but dialysis cannot do this.
What is dialysis?
The kidneys filter and eliminate waste.
The cause might be a chronic, or long-term condition, or an acute problem, such as an injury or a short-term illness that affects the kidneys.
Dialysis prevents the waste products in the blood from reaching hazardous levels. It can also remove toxins or drugs from the blood in an emergency setting.
There are different types of dialysis.
The three main approaches are:
- Intermittent hemodialysis (IHD)
- Peritoneal dialysis (PD)
- Continuous renal replacement therapies (CRRT)
The choice will depend on factors such as the patient's situation, availability, and cost.
In hemodialysis, the blood circulates outside the body of the patient. It goes through a machine with special filters.
The blood comes out of the patient through a flexible tube known as a catheter. The tube is inserted into the vein.
Like the kidneys, the filters remove the waste products from the blood. The filtered blood then returns to the patient through another catheter. The system works like an artificial kidney.
Patients who are going to have hemodialysis need surgery to enlarge a blood vessel, usually in the arm. Enlarging the vein makes it possible to insert the catheters.
Dialysis takes over part of the kidney function when the kidneys no longer work properly.
Hemodialysis is usually done three times a week, for 3-4 hours a day, depending on how well the patient's kidneys work, and how much fluid weight they have gained between treatments.
Hemodialysis can be done in a special dialysis center in a hospital or at home.
Patients who have dialysis at home, or their caregiver, must know exactly what to do. If a person does not feel confident doing dialysis at home, they should attend sessions at the hospital.
Home hemodialysis is suitable for people who:
- Have been in a stable condition while on dialysis
- Do not have other diseases that would make home hemodialysis unsafe
- Have suitable blood vessels for inserting the catheters
- Have a caregiver who is willing to help with hemodialysis
The home environment must also be suitable for taking hemodialysis equipment.
While hemodialysis removes impurities by filtering the blood, peritoneal dialysis works through diffusion.
In peritoneal dialysis, a sterile dialysate solution, rich in minerals and glucose, is run through a tube into the peritoneal cavity, the abdominal body cavity that surrounds the intestine. It has a semi-permeable membrane, the peritoneal membrane.
Peritoneal dialysis uses the natural filtering ability of the peritoneum, the internal lining of the abdomen, to filter waste products from the blood.
The dialysate is left in the peritoneal cavity for some time, so that it can absorb waste products. Then it is drained out through a tube and discarded.
This exchange, or cycle, is normally repeated several times during the day, and it can be done overnight with an automated system.
The elimination of unwanted water, or ultrafiltration, occurs through osmosis. The dialysis solution has a high concentration of glucose, and this causes osmotic pressure. The pressure causes the fluid to move from the blood into the dialysate. As a result, more fluid is drained than is introduced.
Peritoneal dialysis is less efficient than hemodialysis. It takes longer periods, and it removes around the same amount of total waste product, salt, and water as hemodialysis.
However, peritoneal dialysis gives patients more freedom and independence, because it can be done at home instead of going to the clinic several times each week. It can also be done while traveling with a minimum of specialized equipment.
Before starting peritoneal dialysis, the patient needs a small surgical procedure to insert a catheter into the abdomen. This is kept closed off, except when being used for dialysis.
There are two main types of peritoneal dialysis:
Continuous ambulatory peritoneal dialysis (CAPD) requires no machinery and it can be done by the patient or a caregiver.
The dialysate is left in the abdomen for up to 8 hours and then replaced with a fresh solution straight away. This happens every day, four or five times per day.
Continuous cyclic peritoneal dialysis (CCPD) uses a machine to exchange the fluids. It is generally done every night, while the patient sleeps.
Each session lasts from 10 to 12 hours. After spending the night attached to the machine, most people keep the fluid inside their abdomen during the day. Some patients may need another exchange during the day.
Peritoneal dialysis is a suitable option for patients who find hemodialysis too exhausting, such as elderly people, infants, and children. It can be done while traveling, so it is more convenient for those who work or attend school.
Continuous renal replacement therapy
Dialysis can be intermittent or continuous. While a session of intermittent dialysis lasts for up to 6 hours, continuous renal replacement therapies (CRRT) are designed for 24-hour use in an intensive care unit (ICU).
There are different types of CRRT. It can involve either filtration or diffusion. It is better tolerated than intermittent dialysis, because the solute or fluid removal is slower. This leads to fewer complications.
Sometimes dialysis is given for a limited period of time.
People who may benefit from temporary dialysis include those who:
- Have a sudden, or acute, kidney condition
- Have consumed toxic substances or taken a drug overdose
- Have had a traumatic injury to the kidney
- Have chronic heart disease
In some cases, the kidneys recover and do not need further treatment.
Does dialysis replace the kidneys?
Dialysis helps patients whose kidneys have failed, but it is not as efficient as a normal kidney. Patients who receive dialysis need to be careful about what and how much they drink and eat, and they need to take medication.
Many people who have dialysis can work, lead normal lives, and travel, as long as dialysis treatment is possible at the destination.
Women who have dialysis normally have difficulty becoming pregnant. There will be a higher level of waste products in the body than there are with normal kidneys. This interferes with fertility.
Women who do become pregnant while on dialysis will probably need increased dialysis during the pregnancy. If a woman has a successful kidney transplant, her fertility should return to normal.
Dialysis has some effect on male fertility, but less than on female fertility.
Chronic kidney failure happens gradually. Even if just one kidney works, or both work partially, normal kidney function is still possible. It can be a long time before the symptoms of a kidney condition appear.
Blood or protein in the urine can be a sign of kidney failure.
When symptoms do occur, they often vary between individuals, making it harder to diagnose kidney failure quickly.
Symptoms of kidney failure may include:
- Fatigue, or tiredness
- Increasingly frequent need to urinate, especially at night
- Itchy skin
- Erectile dysfunction, when a man has difficulty sustaining an erection
- Shortness of breath
- Water retention, leading to swollen feet, hands, and ankles
- Blood in urine
- Protein in urine
A sudden injury can cause kidney failure. When it does, symptoms tend to appear faster and progress more rapidly.
Anemia is common in people with chronic kidney disease. It can happen when levels of erythropoietin (EPO) are low. EPO is a produced by the kidneys, and it helps the body produce red blood cells. When the red blood cell count is low, it is called anemia.
People who depend on kidney dialysis may experience:
- Muscle cramps
- Itchy skin, often worse before or after a procedure
- Low blood pressure, particularly in people with diabetes
- Sleep problems, sometimes due to itchiness, restless legs, or small breaks in breathing, known as apnea
- Fluid overload, so patients must consume a fixed amount of fluid each day
- Infections or ballooning at the access site for dialysis
- Depression and mood fluctuations
Kidney disease is a serious condition. In people with chronic kidney failure, the kidneys are unlikely to recover, but dialysis can enhance wellbeing and prolong life for up to 20 years or more.
Learn more about the causes and types of kidney failure.