What is hemodialysis?

Hemodialysis is one of the methods of renal replacement therapy in patients with end-stage chronic or acute renal failure, which removes the end products of metabolism – creatinine and urea, as well as free water. The method is based on the principle of diffusion and convection of substances with small and medium molecular weights through a semipermeable membrane, which makes it possible to remove toxic substances and metabolic products from the blood.

 

What is the principle of operation?

Hemodialysis is performed using an artificial kidney machine. The device consists of the following components: a device for blood supply, a device for preparing and supplying dialysis solution, a monitor, a dialyzer. The most important function is performed by a dialyzer. It contains a semipermeable membrane based on cellulose or artificial polymers. The membrane has an area of 0.2 to 2 m², a thickness of 8, 11, 15 or 30 microns, and a pore diameter of 0.5 to 5 nm. It divides the internal space of the dialyzer into two parts (for blood and solution), each of which has its own entrance and exit. Blood taken from the patient’s vessels enters the dialyzer and is located on one side of the membrane, on the other side there is a solution that is similar in electrolyte composition to the composition of blood. Substances with a small molecular weight are removed by diffusion of a lower concentration through the membrane (electrolytes, urea, creatinine, uric acid, etc.). Ultrafiltration removes excess water and substances with a large molecular weight (up to 30,000). Purified blood returns to the patient’s blood vessels.

 

Who is indicated for hemodialysis?

The need for hemodialysis occurs with severe kidney diseases, or when a large amount of toxic substances enters the blood. The method is used when the glomerular filtration rate of the kidneys decreases to 15-10 mL/min, accompanied by an increase in the concentration of blood urea <30 mmol/L, creatinine – <700 mmol/L, as well as when patients have hyperkalemia, metabolic acidosis. This condition can be accompanied by symptoms such as nausea, vomiting, swelling, and fatigue. However, even if the patient does not yet have these symptoms, there may still be high levels of metabolic products in the blood that can be toxic.

Common causes of kidney failure include:

• Diabetes
• High blood pressure (hypertension)
• Inflammation of the kidneys (glomerulonephritis)
• Inflammation of the blood vessels (vasculitis)
• Kidney cysts (polycystic kidney disease)

In addition, the kidneys may suddenly stop (acute kidney damage) after a serious illness, complex surgery, heart attack, or other serious problem. Some medications can also cause kidney damage.

Your doctor will help you determine when to start hemodialysis based on several factors, including:

• General health status
• Kidney function
• Signs and symptoms
• Quality of life
• Personal preferences

In general, hemodialysis helps the body control blood pressure and maintain a proper balance of fluids and electrolytes, such as potassium and sodium. Usually, hemodialysis begins long before kidney function is disrupted so much that it causes life-threatening complications.

 

Risks of hemodialysis

Most people who need hemodialysis have various health problems. Hemodialysis prolongs the life of many people, but the life expectancy of people on hemodialysis is still shorter than in the general population.

Although hemodialysis treatment may be effective in replacing some of the lost kidney function, patients may experience some of the comorbidities listed below, although not everyone faces all of these problems

• Low blood pressure (hypotension). A drop in blood pressure is a common side effect of hemodialysis, especially if you have diabetes. Low blood pressure can be accompanied by shortness of breath, abdominal cramps, muscle spasms, nausea, or vomiting.
• Muscle cramps. Although the cause is unclear, muscle cramps are common during hemodialysis. Sometimes cramps can be relieved by adjusting the hemodialysis procedure. Regulating fluid and sodium intake between hemodialysis procedures can also help prevent symptoms during treatment.
• Itching. Many people undergoing hemodialysis may experience itchy skin, which often worsens during or immediately after the procedure.
• Sleep problems. People who receive hemodialysis often have sleep problems, sometimes due to interruptions in breathing during sleep (sleep apnea).
• Anemia. Lack of sufficient red blood cells in the blood (anemia) is a common complication of renal failure and hemodialysis. Kidney failure is accompanied by a decrease in the production of a hormone called erythropoietin, which stimulates the formation of red blood cells. Dietary restrictions, poor iron absorption, frequent blood tests, or the elimination of iron and vitamins by hemodialysis can also contribute to the development of anemia.
• Bone diseases. If the damaged kidneys are no longer able to process vitamin D, which helps absorb calcium, the bones may weaken. In addition, excessive production of parathyroid hormone – a common complication of kidney failure – can release calcium from the bones.
• Fluid overload. Because the fluid is removed during a hemodialysis procedure, drinking more fluids than recommended between hemodialysis procedures can cause life-threatening complications, such as heart failure or fluid buildup in the lungs (pulmonary edema).
• High potassium levels (hyperkalemia). Potassium is a mineral that is usually eliminated from the body by the kidneys. If the patient consumes more potassium than recommended, the potassium level may become too high. In severe cases, excessive amounts of potassium can cause cardiac arrest.
• Complications of vascular access. Potentially dangerous complications, such as infection, narrowing or swelling of the vessel wall (aneurysm), or blockage, can affect the quality of hemodialysis.

What are the possible accesses for conducting the HD?

There are three types of access:

• Arteriovenous (AV) fistula. A surgically created AV fistula is a connection between an artery and a vein, usually on the arm, that the patient is less likely to use. This is the best type of access because of its efficacy and safety in chronic hemodialysis.
• AV-graft. If the blood vessels are too small to form an AV fistula, the surgeon can instead create a pathway between the artery and vein using a flexible synthetic tube called a graft.
• Central vein catheterization. If emergency hemodialysis is required, a special dialysis catheter can be inserted into a large vein in the neck or near the groin. The catheter is temporary.

How is hemodialysis performed?

During the procedures, the patient sits or lies on the couch while their blood flows through a dialyzer – a filter that acts as an artificial kidney to purify the blood. The patient can use this time to watch TV or a movie, read or sleep.

Preparation. The patient’s weight, blood pressure, pulse, and temperature are checked. The skin at the access point is cleaned.
Beginning. During hemodialysis, two needles are inserted into the arm through the access point and fixed with a patch. Each needle is attached to a flexible plastic tube that connects to the dialyzer. With a single tube, the dialyzer filters the blood, allowing metabolic products and fluids to pass from the blood to a cleansing fluid called dialysate. The filtered blood returns to the body through a second tube.
Symptoms. The patient may experience nausea and abdominal cramps when removing excess fluid, especially if HD is performed only three times a week, and not more often.
Monitoring. Since blood pressure and heart rate can fluctuate when excess fluid is removed, these indicators are constantly monitored during the procedure.
Completion. After hemodialysis is completed, the needles are removed from the access point and a tight bandage is applied to prevent bleeding. The patient’s weight is recorded again.

The duration of one hemodialysis session depends on the technique, and on average is 4-6 hours.