Dialysis: Types, Mechanism, Principle, Function, & Procedure

Dialysis: Types, How It Works, Procedure, Side Effects, Types, Effectiveness

Edited By Irshad Anwar | Updated on Jul 02, 2025 06:44 PM IST

Dialysis is a medical procedure used to remove waste products, excess fluids, and toxins from the blood when the kidneys fail to function properly. It mimics the filtration process of healthy kidneys and helps maintain a balance of electrolytes. In this article, dialysis, the principle of dialysis, types of dialysis, dialysis function, mechanism of dialysis, and dialysis procedure are discussed. Dialysis is a topic of the chapter Excretory Products And Their Elimination in Biology.

This Story also Contains

What is Dialysis?
Principle of Dialysis
Types of Dialysis
Dialysis Function
Mechanism of Dialysis
Dialysis Procedure

Dialysis

What is Dialysis?

Dialysis is one medical process that performs all the functions of the kidneys if they lose their ability to function productively. Dialysis is referred to as the process of removing any form of waste products and excess fluid from the blood because the kidneys fail to excrete in urine. Dialysis helps patients with kidney failure, and it is a life-saving treatment.

The normal function of dialysis involves the balancing of fluids, electrolytes, and waste products in the body in case of improper functioning of the kidney. It can relieve symptoms of kidney failure and make life better for these patients.

Principle of Dialysis

Dialysis includes the idea of solute dissipation and the ultrafiltration of fluid across a semipermeable membrane. Materials in water that have a propensity to flow against a concentration gradient are said to exhibit diffusion.

Dialysate or other specific dialysis fluids flow on one side of the semi-permeable screen while blood flows on the other. A thin layer of material with holes or pores of varying sizes is called a selectively permeable layer.
Smaller fluids and solutes pass through the layer, but larger substances (such as large proteins and red blood cells) are blocked from passing through by the membrane. This mimics the kidneys' filtering process when blood enters them and the larger chemicals are separated from the smaller ones in the glomerulus.

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Types of Dialysis

The two main types of dialysis are hemodialysis and peritoneal dialysis. While they purify waste and excess fluid from the blood in essentially the same way, both ways differ in the method and equipment utilised.

Hemodialysis

Hemodialysis is when blood is filtered by a machine outside the body to remove waste products and excess fluid.
Blood is withdrawn from the body, then filtered in the dialyser, and then returned to the body.

Components

Dialyzer: This is the artificial kidney for filtering the waste products in the blood.
Dialysis Machine: It controls the blood and dialysate flows.
Vascular Access: The site through which blood would be removed and returned.

Advantages And Disadvantages

Works well at removing wastes, suitable for a hospital or clinic setting.
Needs to visit a dialysis centre a few times a week, which tends to cause complications at the access site.

Peritoneal Dialysis

Peritoneal Dialysis is conducted by using the lining of one's abdomen-(peritoneum) as a no-nonsense filter to take out excess waste products and fluid from the body.
Fill the abdominal cavity with dialysis fluid; it takes up the waste products and is drained out.
Dialysis Fluid: Fluid to carry off waste
Catheter: Tube placed in the abdomen to exchange fluid
Can be conducted at home, flexible, and independent.
Prone to infections and involves the installation of a permanent catheter in the abdomen.

Dialysis Function

Dialysis tries to mimic the normal function of the kidneys through a process known as diffusion and osmosis, which leads to excluding excess fluid from the blood and filtering waste products.

Wastes move from high concentrated amount in blood to low concentrated amount in dialysate through a semi-permeable membrane.
Excess fluid in the blood moves through osmosis into the dialysate.
Dialysate – a fluid through which waste products are removed and through which the electrolyte balance is maintained.
Composed specifically, it draws the waste products out from the blood while replenishing what is necessary.
Hemodialysis: In hemodialysis, blood is filtered through a dialyzer.
Peritoneal dialysis: The peritoneum acts as the filter in peritoneal dialysis.

Mechanism of Dialysis

After passing through the dialyser, the arterial blood returns to the body via the vein. When the blood is being sent through the machine, heparin is utilised as an anticoagulant. The hemofilter, which has microscopic channels sandwiched between two cellophane membranes, is where the blood passes through inside the dialyser.

These membranes are permeable. These membranes' outside surface is submerged in dialysate, a dialysing fluid. Fresh dialysate is continuously added to replace the old one. The concentration gradient allows undesirable chemicals from the blood, such as creatinine, phosphate, and urea, to enter the dialysate. The dialysate diffuses into the blood, containing the vital elements the body needs.

The cellophane membranes allow the exchange of nearly all chemicals between the dialysate and blood, with the exception of plasma proteins. Additionally, the dialysis machine contains multiple blood pumps that are equipped with pressure monitors to facilitate the simple transfer of blood from the patient to the machine and back again. Additionally, it features pumps for both the drainage of used dialysate and the flow of fresh dialysate.

Dialysis Procedure

Whenever the kidney capacity drops, the patient has to undergo an appropriate number of dialysis sessions.

Hemodialysis

A session of withdrawing blood out of the body, passing it through a filter, and again returning it into the body.
Three times a week, and each session would be roughly about 3-5 hours.

Peritoneal Dialysis

Continuous Ambulatory Peritoneal Dialysis (CAPD): These are manual exchanges performed throughout the day.
Automated Peritoneal Dialysis (APD): These machine-assisted exchanges are usually performed overnight.
The introduction of dialysis fluid into the abdomen, dwelling, and then draining out from it.
CAPD requires multiple daily exchanges; APD is usually performed nightly.

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Characteristics of Urine	Disorders of the Excretory System
Glomerular Filtrationion Rate	Ammonotelism

Frequently Asked Questions (FAQs)

1. What are the different types of dialysis?

The major types of dialysis include hemodialysis and peritoneal dialysis. These two major types use different techniques to filter waste from the blood.

2. How does dialysis work?

The process of dialysis is based on the principles of diffusion and osmosis. It eliminates waste products and extra fluid from the blood either through an external machine or across the peritoneum lining the inside of the abdomen.

3. What is dialysis given for?

Indicated in chronic kidney diseases, acute kidney injuries, and, for instance, in cases of chronic fluid retention and azotemia symptoms, among others.

4. Enumerate common complications that result from dialysis.

Regular complications are hypotension, muscle cramps, infections, and access site problems. The long-term ones are amyloidosis and cardiac disease.

5. What are some common side effects of hemodialysis?

Common side effects of hemodialysis include low blood pressure (hypotension), muscle cramps, itching, nausea, headaches, and fatigue. These are often related to the rapid changes in blood chemistry and fluid balance during treatment. Long-term effects can include anemia, bone disease, and increased risk of infections.

6. How does peritoneal dialysis increase the risk of peritonitis?

Peritoneal dialysis increases the risk of peritonitis (inflammation of the peritoneum) because it involves repeatedly introducing fluid into the abdominal cavity through a catheter. This creates a potential pathway for bacteria to enter the peritoneum. Proper hygiene and sterile technique during catheter care and dialysis exchanges are crucial to minimize this risk.

7. What is dry weight in dialysis patients and why is it important?

Dry weight is the patient's weight when they have no excess fluid in their body. It's important because it serves as a target for fluid removal during dialysis. Achieving the correct dry weight helps prevent complications like hypertension, shortness of breath, and edema associated with fluid overload.

8. How does dialysis affect the body's ability to produce erythropoietin?

Dialysis doesn't directly affect erythropoietin production, but kidney failure (the reason for dialysis) does. Healthy kidneys produce erythropoietin, which stimulates red blood cell production. In kidney failure, erythropoietin production decreases, often leading to anemia. Many dialysis patients require synthetic erythropoietin to manage this condition.

9. What is the role of anticoagulants in hemodialysis?

Anticoagulants, typically heparin, are used in hemodialysis to prevent blood clotting in the dialysis circuit. As blood flows through the dialysis machine and comes into contact with foreign surfaces, it has a tendency to clot. Anticoagulants ensure that blood flows smoothly through the system, maintaining the efficiency of the dialysis process.

10. How does dialysis affect a patient's diet and fluid intake?

Dialysis patients often need to follow a restricted diet and limit fluid intake. This is because dialysis can't fully replace kidney function in regulating minerals like potassium, phosphorus, and sodium, or in removing excess fluids. Dietary restrictions help prevent the buildup of these substances between dialysis sessions.

11. Why might a patient choose peritoneal dialysis over hemodialysis?

A patient might choose peritoneal dialysis because it offers more flexibility and independence. It can be done at home, allows for a more liberal diet, and doesn't require as strict a fluid restriction. It also preserves residual kidney function longer and may be gentler on the cardiovascular system.

12. How does dialysis affect potassium levels in the body?

Dialysis plays a crucial role in managing potassium levels in patients with kidney failure. During dialysis, excess potassium is removed from the blood. However, this removal can sometimes be too rapid, potentially leading to arrhythmias. Conversely, potassium can accumulate quickly between dialysis sessions, necessitating dietary restrictions. Balancing potassium removal during dialysis with dietary intake is an important aspect of patient care.

13. How does dialysis affect cardiovascular health?

Dialysis can have both positive and negative effects on cardiovascular health. While it helps manage fluid overload and certain metabolic imbalances that stress the heart, the process itself can cause rapid fluid shifts and electrolyte changes that strain the cardiovascular system. Long-term dialysis patients often face increased risks of cardiovascular disease due to chronic inflammation, vascular calcification, and other factors.

14. What is the concept of "dialysis vintage" and why is it significant?

"Dialysis vintage" refers to the length of time a patient has been on dialysis. It's significant because longer dialysis vintage is often associated with increased complications and mortality risk. This is partly due to the cumulative effects of dialysis-related issues like cardiovascular stress, infection risks, and the progression of comorbid conditions over time.

15. How does dialysis mimic the function of healthy kidneys?

Dialysis mimics kidney function by filtering blood through a semipermeable membrane. This membrane allows waste products and excess fluids to pass through while retaining essential blood components like cells and proteins, similar to how healthy kidneys filter blood in the body.

16. What is the role of bicarbonate in dialysis fluid?

Bicarbonate in dialysis fluid plays a crucial role in managing acid-base balance. Kidney failure often leads to metabolic acidosis, and the bicarbonate in the dialysate helps neutralize excess acid in the blood. The concentration of bicarbonate in the dialysate is carefully adjusted to achieve optimal acid-base balance without causing alkalosis.

17. How does ultrafiltration work in dialysis?

Ultrafiltration is the process of removing excess fluid from the blood during dialysis. It works by creating a pressure gradient across the dialysis membrane, causing water and dissolved solutes to move from the blood into the dialysate. The amount of fluid removed can be precisely controlled to achieve the patient's target dry weight.

18. What is the concept of "middle molecules" in dialysis?

"Middle molecules" refer to substances with molecular weights between those of small molecules (like urea) and large proteins. Many of these molecules are uremic toxins that accumulate in kidney failure. Standard hemodialysis is less effective at removing these middle molecules. Newer dialysis techniques and high-flux membranes aim to improve the clearance of these substances.

19. How does dialysis affect the immune system?

Dialysis can impact the immune system in several ways. The repeated exposure of blood to foreign surfaces in the dialysis circuit can activate immune cells, leading to chronic inflammation. Additionally, the removal of certain immune mediators during dialysis and the uremic state itself can contribute to immune dysfunction. This can make dialysis patients more susceptible to infections.

20. What is the difference between low-flux and high-flux dialyzers?

Low-flux and high-flux dialyzers differ in the size of molecules they can remove from the blood. Low-flux dialyzers have smaller pores and primarily remove small molecules like urea and creatinine. High-flux dialyzers have larger pores that can also remove larger molecules like beta-2 microglobulin, potentially providing more effective dialysis for some patients.

21. How does online hemodiafiltration differ from standard hemodialysis?

Online hemodiafiltration combines aspects of hemodialysis and hemofiltration. It uses a high-flux dialyzer and adds convective transport (pushing fluid across the membrane) to diffusive transport. This allows for the removal of a wider range of molecule sizes and can potentially provide more effective clearance of certain uremic toxins compared to standard hemodialysis.

22. What is dialysis adequacy and how is it measured?

Dialysis adequacy refers to how well dialysis is removing waste products from the blood. It's typically measured using the Kt/V ratio, where K is the dialyzer clearance, t is the treatment time, and V is the volume of water in the patient's body. A higher Kt/V indicates more effective dialysis.

23. How does residual kidney function impact dialysis treatment?

Residual kidney function refers to any remaining ability of the patient's own kidneys to filter blood and produce urine. Preserving residual function is important because it contributes to overall health, allows for more flexible fluid and dietary restrictions, and can improve quality of life. Dialysis prescriptions may be adjusted to account for and preserve residual kidney function.

24. How does dialysis affect bone metabolism?

Dialysis can negatively impact bone metabolism due to the disruption of calcium and phosphorus balance in the body. Kidney failure leads to decreased vitamin D activation and increased parathyroid hormone levels. This, combined with dietary restrictions and the dialysis process itself, can lead to a condition called renal osteodystrophy, characterized by weakened bones.

25. How does hemodialysis work?

In hemodialysis, blood is pumped out of the body through a dialysis machine. The machine filters waste products and excess fluids from the blood using a special solution called dialysate. The cleaned blood is then returned to the body. This process typically takes 3-5 hours and is usually done 3 times a week.

26. What is the principle behind peritoneal dialysis?

Peritoneal dialysis uses the peritoneum, the lining of the abdominal cavity, as a natural filter. A special fluid called dialysate is introduced into the abdominal cavity through a catheter. The peritoneum allows waste products and excess fluids to pass from the blood into the dialysate, which is then drained out of the body.

27. What is an arteriovenous fistula and why is it important for hemodialysis?

An arteriovenous fistula is a surgically created connection between an artery and a vein, usually in the arm. It's important for hemodialysis because it provides a strong, reliable access point for repeated needle insertions, allowing for efficient blood flow during the dialysis procedure.

28. How does the dialyzer in a hemodialysis machine work?

The dialyzer, often called an artificial kidney, contains thousands of hollow fibers with microscopic pores. As blood flows through these fibers, waste products and excess fluids pass through the pores into the surrounding dialysate solution, while larger molecules like blood cells and proteins remain in the blood.

29. What is dialysate and why is its composition important?

Dialysate is a specially formulated solution used in dialysis to help remove waste products from the blood. Its composition is crucial because it determines which substances are removed from or added to the blood during dialysis. The dialysate's electrolyte concentrations are carefully balanced to ensure proper blood chemistry after treatment.

30. What is the concept of "incremental dialysis" and how does it differ from standard initiation?

Incremental dialysis refers to a gradual approach to initiating dialysis, where treatment is started at a lower frequency or intensity and gradually increased as needed. This contrasts with the standard approach of starting with full-dose, thrice-weekly hemodialysis. Incremental dialysis aims to preserve residual kidney function longer and may offer quality of life benefits for some patients.

31. How does dialysis affect medication dosing and pharmacokinetics?

Dialysis can significantly affect medication dosing and pharmacokinetics. Some drugs may be removed by dialysis, requiring dose adjustments or administration after dialysis sessions. The altered physiology in dialysis patients (e.g., changes in fluid volume, protein binding, and metabolic pathways) can also affect drug distribution and elimination, necessitating careful medication management.

32. How does dialysis affect mineral and bone disorder in chronic kidney disease?

Dialysis impacts mineral and bone disorder in chronic kidney disease (CKD-MBD) through several mechanisms. It helps remove excess phosphorus but can also lead to calcium losses. The inability to activate vitamin D and the disruption of normal regulatory mechanisms can lead to secondary hyperparathyroidism. Managing this complex interplay of minerals, hormones, and bone metabolism is a crucial aspect of dialysis patient care.

33. What is the role of ultrafiltration profiling in hemodialysis?

Ultrafiltration profiling involves varying the rate of fluid removal during a hemodialysis session. The goal is to optimize fluid removal while minimizing cardiovascular stress and symptoms like hypotension. By tailoring the ultrafiltration rate to the patient's cardiovascular tolerance, typically with higher rates early in the session an

34. What are the two main types of dialysis?

The two main types of dialysis are hemodialysis and peritoneal dialysis. Hemodialysis uses an external machine to filter blood, while peritoneal dialysis uses the lining of the abdominal cavity (peritoneum) as a natural filter.

35. What is the difference between continuous and intermittent dialysis?

Continuous dialysis, such as continuous ambulatory peritoneal dialysis (CAPD), involves ongoing treatment throughout the day and night. Intermittent dialysis, like standard hemodialysis, involves scheduled treatment sessions, typically three times a week for several hours each time.

36. What is nocturnal dialysis and how does it differ from standard hemodialysis?

Nocturnal dialysis is a form of hemodialysis performed while the patient sleeps, typically for 6-8 hours per night, 3-6 nights per week. It differs from standard hemodialysis in that it allows for slower, more gradual fluid and waste removal, which can be gentler on the body. This extended treatment time often results in better clearance of waste products and improved quality of life for patients.

37. What is the role of sodium profiling in hemodialysis?

Sodium profiling is a technique used in hemodialysis where the sodium concentration in the dialysate is varied during the treatment session. The goal is to improve cardiovascular stability and reduce symptoms like cramping and hypotension. By starting with a higher sodium concentration and gradually decreasing it, fluid removal can potentially be optimized while minimizing adverse effects.

38. What is dialysis and why is it necessary?

Dialysis is a medical procedure that filters waste products and excess fluids from the blood when the kidneys are unable to do so effectively. It's necessary for patients with kidney failure or severe kidney dysfunction to maintain proper blood chemistry and fluid balance in the body.

39. What is the concept of "dialysis dose" and how is it determined?

Dialysis dose refers to the amount of dialysis a patient receives, typically measured by Kt/V or URR. The dose is determined based on factors like the patient's body size, residual kidney function, metabolic needs, and clinical status. Adequate dosing is crucial for effective waste removal and symptom management. The dose may be adjusted over time based on the patient's response and changing needs.

40. What is the concept of "dialysis adequacy" and how is it measured?

Dialysis adequacy refers to how well dialysis is removing waste products from the blood. It's typically measured using the Kt/V ratio and urea reduction ratio (URR). Kt/V takes into account the dialyzer clearance (K), treatment time (t), and the patient's volume of distribution (V). URR measures the percentage reduction in blood urea nitrogen during a dialysis session. These measurements help ensure that patients are receiving sufficient dialysis.

41. What is the concept of "dialysis vintage" and how does it relate to patient outcomes?

Dialysis vintage refers to the length of time a patient has been on dialysis. It's an important factor in assessing patient outcomes because longer vintage is often associated with increased complications and mortality risk. This relationship is due to the cumulative effects of dialysis-related issues, progression of comorbidities, and the challenges of long-term renal replacement therapy. Understanding dialysis vintage helps in individualizing care and setting appropriate treatment goals.

42. What is dialysis disequilibrium syndrome?

Dialysis disequilibrium syndrome is a rare but serious complication that can occur during or after hemodialysis, especially in new patients or those who have missed treatments. It's characterized by neurological symptoms like headache, nausea, and in severe cases, seizures or coma. It's thought to be caused by rapid changes in blood osmolality during dialysis, leading to brain swelling.

43. How does dialysis affect sleep patterns and quality?

Dialysis can significantly impact sleep patterns and quality. Factors contributing to sleep disturbances in dialysis patients include the treatment schedule (especially for in-center hemodialysis), uremic symptoms, restless leg syndrome, sleep apnea, and psychological factors like anxiety and depression. Managing these issues is important for improving overall quality of life in dialysis patients.

44. How does dialysis affect cognitive function in patients?

Dialysis can have complex effects on cognitive function. While it helps clear uremic toxins that can impair cognition, the process itself can sometimes lead to short-term cognitive fluctuations. Factors like rapid fluid and electrolyte shifts, cerebral edema, and the stress of treatment can impact cognitive performance. Long-term dialysis patients may also face risks of cognitive decline due to various factors including vascular disease and chronic inflammation.

45. How does dialysis affect nutritional status and metabolism?

Dialysis can significantly impact nutritional status and metabolism. The process itself can lead to nutrient losses, including amino acids and water-soluble vitamins. Dietary restrictions necessary for managing electrolytes and fluid balance can sometimes lead to inadequate nutrient intake. Additionally, the catabolic nature of kidney disease and the inflammatory state associated with dialysis can increase nutritional needs. Careful nutritional management is crucial for dialysis patients.

46. How does dialysis affect the cardiovascular system over time?

Long-term dialysis can have significant effects on the cardiovascular system. The repeated cycles of fluid removal and accumulation can lead to cardiac remodeling and hypertrophy. Chronic inflammation, altered mineral metabolism, and accelerated atherosclerosis contribute to increased cardiovascular risk. Vascular calcification is also more common in dialysis patients. Managing these cardiovascular effects is a key aspect of long-term dialysis care.