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Dialysis

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Biology

The kidney is in charge of filtering extra fluid and waste materials out of the blood and turning them into urine which is then transported to the bladder where they are stored until urination.

Dialysis attempts to artificially perform the function of the kidneys and maintain the balance of the fluids (water) and electrolytes in the blood when the kidneys are not working sufficiently.

Kidney damage can occur as a result of a variety of factors, including persistent high blood pressure, type 2 diabetes, or even a severe accident.

Read our article Diabetes to learn more about this very predominant disease!

The purpose of dialysis treatment

One kidney should be enough for people to survive, but if both fail, it can lead to death if not addressed. The ultimate therapy for complete renal failure is a kidney transplant, however, this requires the patient to meet all of the requirements and be placed on a long waiting list. Kidney dialysis is a temporary solution for those who are awaiting a kidney transplant or who are ineligible for organ transplantation.

All of the blood in our body passes through the kidneys once every 5 minutes, filtering a staggering 180 litres of water during the day. Check out our Kidney article to learn more about this organ!

Extra water, waste (urea) and mineral ions are prevented from collecting in your body by healthy kidneys. They also aid in the regulation of blood pressure and the amounts of electrolytes in the blood. Sodium and potassium are examples of these substances. kidneys also activate vitamin D which is important in promoting calcium absorption.

When the kidneys are unable to accomplish their tasks due to disease or injury, dialysis can assist in maintaining the body functioning as close to normal as possible. Without dialysis treatment, toxins and other waste products build up in the blood, contaminating the body and causing harm to other organs and damaging cells by osmosis.

Kidney dialysis types

There are three types of dialysis that are currently available to patients and each has its own advantages and disadvantages.

Haemodialysis

Hemodialysis is the most prevalent form of dialysis and the one you are most likely familiar with. An artificial kidney (dialysis machine or dialyzer) is used in this procedure to eliminate waste and excess fluid from the blood. The blood is taken from the body and purified by the dialysis machine before being returned back to the body.

This procedure requires doctors to perform surgery to construct an entrance site into your blood vessels in order to start the blood flowing to the dialysis machine.

There are three types of entry points used for haemodialysis:

  1. Arteriovenous (AV) fistula: This kind is used to surgically link an artery and a vein. It is often the recommended choice.
  2. AV graft: A looped tube is used to connect one of the arteries and veins in the arm. The blood is then taken from the tube and is returned to it after running through the dialysis machine.
  3. Vascular access catheter: This is likely to be placed into a major vein in the neck and is often used for short-term purposes.
The AV fistula and graft are both intended for long-term dialysis therapy. Two to three months following surgery, patients with AV fistulas are healed and ready to begin hemodialysis. People who get AV grafts can return to work in two to three weeks.

The unfiltered, high-urea blood that is drawn from the body is combined with a form of blood thinner or an anticoagulant to avoid clotting before being pumped into the dialysis machine.

Dialysis Machine

The unfiltered, high-urea blood that is drawn from the body is combined with a form of blood thinner or an anticoagulant to avoid clotting before being pumped into the dialysis machine. Inside the machine, a semi-permeable membrane keeps the blood separate from the dialysis fluid while they flow in opposite directions. This is called a countercurrent flow and it allows for the maximum exchange possible by maintaining the concentration gradient between the blood and the dialysis fluid.

The process replicated by the dialysis machine, much like in the kidney itself relies on molecules diffusing down their concentration gradient! Read our article Diffusion to learn more about how this happens!

The dialysis fluid contains the same concentration of glucose and electrolytes that are found in normal blood plasma while containing no urea. As a result, any abnormal excess of glucose or other electrolytes, as well as the majority of urea in the blood, are filtered out by diffusion into the dialysis fluid. The removal of the urea is a very important part of dialysis.

Urea is a nitrogenous waste product resulting from the metabolic breakdown of proteins used in all mammals. Urea is produced in the liver, removed from circulation in the kidney and excreted via urine. Urea is very toxic and if wasn't removed it would cause damage to different organ systems including the kidney itself, bone marrow, intestinal tract or the blood vessels for example.

The majority of hemodialysis treatments are administered in a hospital, doctor's office, or dialysis clinic. Hemodialysis treatments are normally three to five hours long and have to be done approximately three times each week. The duration of the dialysis is determined by the amount of waste your body produces, your weight, and the present status of your health. After you've been on hemodialysis for a while, you may become eligible for performing the dialysis treatments at home. This is called home haemodialysis and is a convenient alternative for patients who are on long-term dialysis.

Haemodialysis side effects

Low blood pressure is one of the most prevalent adverse effects of haemodialysis. The fall in fluid levels during dialysis is the potential cause of this. Low blood pressure can in turn lead to lightheadedness, nausea and dizziness. The easiest method to reduce these symptoms is to stick to the fluid consumption guidelines that those undergoing dialyses are given.

Moreover, patients who receive haemodialysis are at a higher risk of acquiring an infection that can develop into sepsis. Dizziness and a high fever are early warning signs of this

Sepsis is an extreme response to infection. It happens when pathogens (usually bacteria) infiltrate the body and circulate via the bloodstream, potentially causing various organ failures.

Muscle cramps, usually in the lower leg, are common during haemodialysis. This is hypothesised to be induced by the muscles' reaction to fluid loss during haemodialysis. Many individuals who get haemodialysis also experience itchy skin as a result of mineral buildup in the body between dialysis treatments.

Peritoneal dialysis

Peritoneal dialysis is a surgical procedure during which a peritoneal dialysis (PD) catheter is inserted into the patient's belly. The catheter aids in filtering the blood through the peritoneum. The dialysis fluid is injected into the peritoneal cavity during the procedure. This fluid is similar to the one used in haemodialysis so it acts like a waste absorber.

The dialysis fluid is then emptied from the abdomen after it has filtered out the wastes from the circulation. The peritoneal dialysis procedure takes a few hours to complete and often has to be done four to six times every day.

The peritoneum is a double-layered serous membrane that lines the cavity of the abdomen and surrounds the abdominal organs. The space between the peritoneal membranes is called the peritoneal cavity.

Peritoneal dialysis side effects

Bacterial infection of the peritoneum is a typical adverse effect of peritoneal dialysis. If the dialysis equipment is not maintained sterile, microbes present on the equipment have the potential to move to the peritoneum or even cause sepsis. Furthermore, retaining fluid inside the peritoneal cavity for several hours exerts tension on the abdominal muscles and hence can increase the risk of developing a hernia.

A hernia is a medical condition that occurs when an internal portion of the body pushes through its normal cavity.

Continuous renal replacement therapy (CRRT)

Continuous renal replacement therapy (CRRT) or haemofiltration is a type of dialysis mainly used for people with kidney failure in the intensive care unit. CRRT is a slower form of dialysis that is safer for the heart. It is performed 24 hours a day, rather than over four hours, to gently and constantly clear out waste products and excess fluids from the patient.

Dialysis - Key takeaways

  • Dialysis attempts to perform the function of the kidneys and maintain the balance of the fluids and electrolytes in the blood when the kidneys are not working sufficiently.
  • There are three types of dialysis:
    • Haemodialysis involves running the blood into an artificial kidney or a dialysis machine. Inside the dialysis machine, the blood and the dialysis fluid are separated by a semi-permeable membrane and flow in opposite directions. The waste products in the blood are filtered into the dialysis fluid via diffusion.
    • Peritoneal dialysis involves inserting a catheter into the abdomen and injecting the dialysis fluid into the peritoneal cavity. The peritoneal membrane acts like a semi-permeable membrane filtering the waste products out of the blood.
    • Continuous renal replacement therapy (CRRT) or haemofiltration is a type of dialysis mainly used for people with kidney failure in the intensive care unit.

Dialysis

Dialysis attempts to perform the function of the kidneys and maintain the balance of the fluids and electrolytes in the blood when the kidneys are not working sufficiently.

When the kidneys are unable to accomplish their tasks due to disease or injury, dialysis can assist in maintaining the body functioning as close to normal as possible. Without dialysis treatment, toxins and other waste products build up in the blood, contaminating the body and causing harm to other organs. 

There are three types of dialysis: haemodialysis, peritoneal dialysis, and continuous renal replacement therapy (CRRT) 

The unfiltered, high-urea blood that is drawn from the body is combined with a form of blood thinner or an anticoagulant to avoid clotting before being pumped into the dialysis machine. 


Inside the machine, a semi-permeable membrane keeps the blood separate from the dialysis fluid while they flow in opposite directions. This is called a countercurrent flow and it allows for the maximum exchange possible by maintaining the concentration gradient between the blood and the dialysis fluid.


The dialysis fluid contains the same concentration of glucose and electrolytes that are found in normal blood plasma while containing no urea.  As a result, any abnormal excess of glucose or other electrolytes, as well as the majority of urea in the blood, are filtered out by diffusion into the dialysis fluid. The removal of the urea is a very important part of dialysis. 

One kidney should be enough for people to survive, but if both fail, it can lead to death if not addressed. The ultimate therapy for complete renal failure is a kidney transplant, however, this requires the patient to meet all of the requirements and be placed on a long waiting list. Kidney dialysis is a temporary solution for those who are awaiting a kidney transplant or who are ineligible for organ transplantation.

Final Dialysis Quiz

Question

What is dialysis?

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Answer

Dialysis attempts to perform the function of the kidneys and maintain the balance of the fluids and electrolytes in the blood when the kidneys are not working sufficiently. 

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Question

Name some functions of the kidneys

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Answer

  • Extra water, waste, and other pollutants are prevented from collecting in your body by healthy kidneys. 
  • They aid in the regulation of blood pressure and the amounts of electrolytes in the blood.
  • Your kidneys also activate vitamin D which is important in promoting calcium absorption. 

Show question

Question

What are the three types of dialysis?

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Answer

Haemodialysis, Peritoneal dialysis, and continuous renal replacement therapy (CRRT) 


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Question

In haemodialysis, the blood is separate from the dialysis fluid via a __________. 

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Answer

Semi-permeable membrane

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Question

The blood and the dialysis fluid flow in the same direction

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Answer

False

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Question

What is the content of the dialysis fluid?

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Answer

The dialysis fluid contains the same concentration of glucose and electrolytes that are found in normal blood plasma while containing no urea. 

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Question

What factors determine the duration of each dialysis session?

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Answer

The duration of the dialysis is determined by the amount of waste your body produces, your weight, and the present status of your health.


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Question

How does hemodialysis cause low blood pressure as a side effect?

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Answer

The fall in fluid levels during dialysis is the potential cause of this. Low blood pressure can in turn lead to lightheadedness, nausea and dizziness.  

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Question

Name three side effects of haemodialysis

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Answer

1. infection and sepsis

2. Muscle cramps 

3.  itchy skin 

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Question

What is peritoneal dialysis?

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Answer

Peritoneal dialysis involves inserting a catheter into the abdomen and injecting the dialysis fluid into the peritoneal cavity. The peritoneal membrane acts like a semi-permeable membrane filtering the waste products out of the blood. 

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Question

What is the peritoneum?

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Answer

The peritoneum is a double-layered serous membrane that lines the cavity of the abdomen and surrounds the abdominal organs. The space between the peritoneal membranes is called the peritoneal cavity. 


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Question

How long does each peritoneal dialysis session last?

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Answer

The peritoneal dialysis procedure takes a few hours to complete and often has to be done four to six times every day 

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Question

What are some side effects of peritoneal dialysis?

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Answer

  1. Bacterial infection of the peritoneum 
  2. increased the risk of developing a hernia

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Question

What is CRRT?

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Answer

Continuous renal replacement therapy (CRRT) or haemofiltration 

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Question

When is CRRT usually used?

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Answer

It is mainly used for people with kidney failure in the intensive care unit. CRRT is a slower form of dialysis that is safer for the heart. It is performed 24 hours a day, rather than over four hours 

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