Hemodialysis: How Kidney Dialysis Works and When It Is Needed

Hemodialysis is a treatment that helps remove waste, extra fluid, and toxins from the blood when the kidneys can no longer do this well enough. It can be used for advanced chronic kidney disease, sudden kidney injury, or while a patient is waiting for a kidney transplant.

Overview

Hemodialysis is a kidney replacement therapy used when the kidneys are not able to remove enough waste products, excess water, and certain toxins from the blood. Healthy kidneys filter the blood continuously, help control blood pressure, support red blood cell production, and keep important minerals such as potassium, sodium, and calcium in balance. When kidney function falls to a very low level, hemodialysis can take over part of the filtering work.

During hemodialysis, blood is gently moved from the body through tubing into a dialysis machine. Inside the machine, blood passes through a filter called a dialyzer, sometimes called an artificial kidney. The dialyzer removes waste and extra fluid, and the cleaned blood is returned to the body. The treatment does not cure kidney failure, but it can help patients feel better, reduce complications, and support daily life.

Hemodialysis may be planned in advance for people with chronic kidney disease, or it may be started urgently if sudden kidney failure or severe fluid or chemical imbalance occurs. The decision is individualized and based on symptoms, blood test results, overall health, and the patient’s goals and preferences.

How Hemodialysis Works

The main parts of hemodialysis are the dialysis machine, the dialyzer, dialysis fluid, and a blood access. Blood leaves the body through one needle or catheter line and enters the dialyzer. On the other side of a thin membrane is dialysis fluid, also called dialysate. Waste products and excess minerals move across the membrane from the blood into the dialysate, while blood cells and proteins remain in the bloodstream.

The dialysis machine also helps remove extra fluid. This process is called ultrafiltration. The care team calculates how much fluid should be removed based on the patient’s weight, blood pressure, swelling, urine output, and symptoms. Removing too much fluid too quickly can cause discomfort, so the target is carefully adjusted for safety and comfort.

Hemodialysis also helps correct imbalances such as high potassium, excess acid in the blood, and fluid overload. However, it does not replace every kidney function. Many patients still need medicines for anemia, bone and mineral balance, blood pressure, or other conditions related to chronic kidney disease.

When Hemodialysis Is Needed

Hemodialysis is usually considered when kidney function has declined to the point that the body cannot maintain a safe internal balance. This often happens in advanced chronic kidney disease, also called end-stage kidney disease. It may also be needed temporarily in acute kidney injury, for example after severe illness, major surgery, serious infection, dehydration, medication-related kidney injury, or exposure to certain toxins.

Doctors do not decide to start dialysis based on one number alone. Estimated glomerular filtration rate, blood urea nitrogen, creatinine, potassium, bicarbonate, fluid status, and symptoms are all reviewed together. Some people begin dialysis because of persistent nausea, loss of appetite, fatigue, itching, shortness of breath from fluid buildup, uncontrolled blood pressure, swelling, confusion, or dangerous blood chemistry changes.

Common situations in which hemodialysis may be recommended include:

• Advanced chronic kidney disease with symptoms of toxin buildup
• High potassium or acid levels that cannot be controlled safely with other measures
• Fluid overload causing breathlessness or swelling despite treatment
• Certain poisonings or medication overdoses when dialysis can remove the substance
• Temporary kidney failure where recovery is possible but support is needed

For people with long-term kidney failure, hemodialysis is one of several treatment paths. Other options may include peritoneal dialysis, kidney transplantation, or conservative kidney care focused on symptom control. A nephrologist discusses the benefits, limitations, and practical aspects of each option with the patient and family.

Dialysis Access: Fistula, Graft, and Catheter

Hemodialysis requires a reliable way to move blood from the body to the dialysis machine and back again. This is called vascular access. The type of access depends on how urgently dialysis is needed, the condition of the blood vessels, and how long treatment is expected to continue.

An arteriovenous fistula is often preferred for long-term hemodialysis when it can be created safely. It is made by connecting an artery to a vein, usually in the arm, through a small surgical procedure. Over time, the vein becomes stronger and larger, making it suitable for repeated needle placement. A fistula may take weeks to months to mature before it can be used.

An arteriovenous graft uses a soft synthetic tube to connect an artery and a vein. It may be considered when a fistula is not possible or when access is needed sooner. A central venous catheter is a flexible tube placed into a large vein, often in the neck or chest. Catheters can be used quickly, especially in urgent situations, but they carry a higher risk of infection and clotting, so they are generally not the first choice for long-term use when other options are suitable.

Patients are taught how to protect their access. This may include checking for a vibration or pulse in a fistula or graft, keeping the area clean, avoiding blood pressure measurements or blood draws from the access arm, and reporting redness, swelling, pain, fever, or changes in flow promptly.

What to Expect During a Hemodialysis Session

Hemodialysis is commonly performed in a dialysis center, hospital unit, or, for selected patients, at home after training. In a center-based session, nurses or dialysis technicians check weight, blood pressure, temperature, and general wellbeing before treatment begins. The access is cleaned carefully, and needles are placed into a fistula or graft, or catheter lines are connected using sterile technique.

Many patients have hemodialysis several times per week, with each session lasting a few hours. The exact schedule depends on kidney function, body size, fluid intake, blood test results, symptoms, and the dialysis prescription. During treatment, patients may read, rest, listen to music, or watch a program. The care team monitors blood pressure, machine settings, and comfort throughout the session.

Some people feel tired after dialysis, especially in the early weeks or if a large amount of fluid has been removed. Others feel relief as symptoms of fluid overload or toxin buildup improve. Possible treatment-related symptoms can include muscle cramps, headache, nausea, dizziness, or low blood pressure. These are usually managed by adjusting fluid removal, diet and fluid guidance, medicines, or the dialysis prescription.

Home hemodialysis may be an option for motivated patients with suitable support and training. It offers more flexibility for some people, but it requires careful education, infection prevention, equipment management, and regular follow-up with the dialysis team.

Benefits, Limitations, and Possible Risks

Hemodialysis can help control the effects of severe kidney failure. It removes waste products, helps manage excess fluid, corrects certain chemical imbalances, and may reduce symptoms such as breathlessness, swelling, nausea, and poor appetite. It can also serve as a bridge to kidney transplantation for eligible patients.

At the same time, hemodialysis is a major ongoing treatment that affects daily routines. Patients need regular sessions, blood tests, access care, dietary adjustments, and coordination of medications. Dialysis does not restore normal kidney function completely, and some symptoms or health issues may persist because kidney disease affects the whole body.

Possible risks include access infection, clotting or narrowing of the access, low blood pressure during treatment, muscle cramps, anemia, bone and mineral problems, and heart or blood pressure challenges related to fluid balance. These risks are monitored by the healthcare team, and many can be reduced through careful access care, individualized dialysis prescriptions, nutrition guidance, and regular follow-up.

Patients should feel comfortable asking questions about their dialysis adequacy, laboratory results, access health, transplant eligibility, and treatment alternatives. Shared decision-making helps align treatment with the patient’s medical needs, lifestyle, and personal priorities.

Diet, Fluids, and Self-Care on Hemodialysis

Nutrition and fluid management are important parts of hemodialysis care. Because dialysis is usually performed intermittently, substances such as potassium, phosphorus, sodium, and fluid can build up between sessions. A renal dietitian can provide individualized guidance based on blood results, remaining urine output, other medical conditions, and cultural food preferences.

Many patients are advised to pay attention to salt intake because sodium can increase thirst and fluid retention. Potassium and phosphorus may also need monitoring. High potassium can affect heart rhythm, while high phosphorus can contribute to bone and blood vessel problems over time. Protein needs may be higher on hemodialysis than in earlier stages of chronic kidney disease, because some protein is lost during treatment and the body needs adequate nutrition.

Helpful self-care habits include:

• Attending dialysis sessions as scheduled and discussing any missed treatment with the care team
• Taking prescribed medicines exactly as directed
• Following individualized guidance on fluid, salt, potassium, and phosphorus
• Keeping the dialysis access clean and reporting changes quickly
• Staying active within personal limits and asking about safe exercise
• Keeping vaccination and preventive care plans up to date as recommended by a doctor

Emotional wellbeing also matters. Adjusting to dialysis can take time, and it is normal to have practical or emotional concerns. Support from family, patient educators, social workers, psychologists, and kidney care teams can make treatment easier to manage.

When to See a Doctor

People with known chronic kidney disease should have regular follow-up with a nephrologist, even if they feel well. Early planning allows time to choose a treatment option, prepare a fistula or other access if needed, review transplant eligibility, and learn how to slow kidney decline where possible. Planning ahead can make the start of dialysis safer and less stressful.

Medical advice should be sought promptly if a person with kidney disease develops worsening swelling, shortness of breath, chest discomfort, confusion, severe weakness, persistent vomiting, reduced urination, fever, or signs of access infection such as redness, warmth, drainage, or increasing pain. Patients already on dialysis should also contact their care team if they miss a session, have bleeding from the access site, notice the fistula or graft pulse has changed, or feel unwell after treatment.

For international patients who need evaluation or ongoing kidney care, Acibadem International’s multidisciplinary specialists and JCI-accredited hospitals diagnose and treat kidney failure and provide hemodialysis-related care. Patients should bring previous blood tests, imaging, medication lists, dialysis records, and access information to support an accurate treatment plan.

Frequently asked questions

Is hemodialysis painful?

Hemodialysis itself should not be painful, but needle insertion into a fistula or graft may cause brief discomfort. Some patients may feel tired, dizzy, or have cramps during or after treatment. The dialysis team can adjust the treatment plan and provide comfort measures if symptoms occur.

How long does a person need hemodialysis?

The duration depends on the cause of kidney failure. In acute kidney injury, hemodialysis may be temporary until the kidneys recover. In end-stage chronic kidney disease, it is usually ongoing unless the patient receives a kidney transplant or chooses another treatment approach.

Can kidneys start working again after dialysis begins?

Yes, this can happen when dialysis is started for acute kidney injury or a reversible condition. In long-term advanced chronic kidney disease, recovery of kidney function is less common. Doctors monitor urine output and blood tests to understand whether dialysis is still needed.

What is the difference between hemodialysis and peritoneal dialysis?

Hemodialysis filters the blood through a machine and dialyzer outside the body. Peritoneal dialysis uses the lining of the abdomen as a natural filter and is usually performed at home. The best option depends on medical factors, lifestyle, support at home, and patient preference.

Can a person travel while on hemodialysis?

Many people on hemodialysis can travel with careful planning. Dialysis sessions must be arranged in advance at a suitable center, and medical records should be shared before the trip. Patients should discuss travel plans with their nephrologist and dialysis team early.

Does hemodialysis replace all kidney functions?

No. Hemodialysis replaces some filtering and fluid-removal functions, but it does not fully perform all the hormonal and metabolic roles of healthy kidneys. Patients may still need medications, diet guidance, anemia treatment, bone and mineral management, and regular monitoring.

References

• National Kidney Foundation
• Kidney Disease: Improving Global Outcomes
• National Institute of Diabetes and Digestive and Kidney Diseases
• European Renal Association
• World Health Organization

This article is for general information only and is not a substitute for professional medical advice. Please consult a qualified doctor about your individual situation.