It is normal to feel anxious before beginning dialysis. For many people, the uncertainty about what happens during treatment is more stressful than the individual steps themselves.
Dialysis is a form of kidney replacement therapy. It removes waste products and excess fluid and helps balance electrolytes and the body’s acid-base status. In hemodialysis, bicarbonate in the dialysis fluid commonly helps correct excess acidity in the blood. Peritoneal dialysis solutions also contain a prescribed buffer.
Dialysis replaces only part of normal kidney function. It does not fully replace functions such as producing erythropoietin or activating vitamin D, so medications and other treatments may still be needed.
This guide explains what usually happens during in-center hemodialysis and a peritoneal dialysis exchange. Treatment duration, fluid removal, medications, equipment settings, and exchange schedules are determined by the individual prescription.
What Happens During In-Center Hemodialysis?
Hemodialysis filters blood outside the body using a dialysis machine and a filter called a dialyzer.
A conventional in-center treatment generally follows seven steps.
1. Arrival and Health Checks
Before treatment begins, a member of the dialysis team will usually check your:
- Weight
- Blood pressure
- Temperature
- Pulse
- Current symptoms
- Vascular access
Your weight helps the team estimate how much excess fluid may need to be removed.
This calculation is based partly on your target weight, often called your dry weight. Dry weight is the estimated weight you would have without excess fluid. It can change over time as your health, nutrition, urine production, or fluid status changes.
Tell the dialysis team about new shortness of breath, swelling, dizziness, chest discomfort, fever, medication changes, or access concerns before treatment begins.
2. Vascular Access Assessment
Hemodialysis requires a vascular access that allows blood to travel between your body and the dialysis machine. The main types are:
- An arteriovenous fistula
- An arteriovenous graft
- A central venous catheter
Blood flowing through a fistula or graft normally creates a buzzing or vibrating sensation called a thrill.
Check the thrill every day, or more often if instructed by your dialysis team. Contact the team immediately if it disappears, becomes much weaker, or feels clearly different. Do not wait until your next treatment.
A more complete explanation of access protection is available in Dialysis Access: Caring for Your Lifeline.
3. Connection to the Dialysis Machine
For a fistula or graft, the skin is cleaned with an antiseptic solution and two needles are usually inserted.
One needle carries blood from the body toward the dialyzer. The other returns the filtered blood.
Needle insertion may cause brief stinging or pressure. Ask your dialysis team whether a prescribed numbing cream or another comfort measure is appropriate.
A central venous catheter does not require needle insertion during each treatment. Trained staff connect it directly to the tubing using hand hygiene, hub disinfection, and aseptic technique.
4. Blood Filtration and Fluid Removal
Blood travels through soft tubing into the dialyzer.
Inside the dialyzer, blood and dialysis fluid flow on opposite sides of a thin membrane. Waste products and certain excess electrolytes move across this membrane into the dialysis fluid.
Extra water is removed through ultrafiltration. The dialysis machine creates a controlled pressure difference across the membrane, causing excess water to move out of the blood.
The filtered blood then returns to the body through the vascular access.
To help prevent blood from clotting inside the tubing and dialyzer, many patients receive an anticoagulant, often heparin, during treatment. The medication and dose are individualized, and some patients may need a different approach or no systemic anticoagulant.
5. Monitoring During Treatment
The dialysis machine continuously monitors technical conditions that include:
- The prescribed blood-pump rate
- Pressures within the dialysis circuit
- The fluid-removal rate
- Air detection
- Blood-leak detection
- Other conditions that may affect treatment safety
These machine readings do not directly measure blood flow through the fistula or graft itself.
Clinical staff also check your blood pressure, vascular access, symptoms, and general condition throughout treatment.
Tell the team immediately if you experience:
- Muscle cramps
- Dizziness or lightheadedness
- Nausea
- Headache
- Chest discomfort
- Shortness of breath
- Chills
- Sudden weakness
- Access pain
- Unusual restlessness
Do not wait until the session ends to report symptoms. The team can evaluate whether your position, fluid-removal rate, medication plan, dialysate settings, or another part of treatment needs attention.
6. Disconnection and Post-Treatment Checks
When treatment is complete, blood remaining in the tubing is returned to your body.
If you have a fistula or graft, the needles are removed and pressure is applied until bleeding stops. A dressing is then placed over the needle sites.
If you have a catheter, the lines are disconnected using aseptic technique and the catheter is secured with a clean dressing.
Your post-treatment weight and blood pressure may be checked before you leave. Stand slowly and tell the team if you feel dizzy, weak, nauseated, or unsteady.
7. Recovery After the Session
Some people experience post-dialysis fatigue, which may include tiredness, weakness, sleepiness, or difficulty concentrating after treatment. Other people can continue with their usual activities.
Tell your dialysis team if the fatigue is severe, lasts longer than usual, suddenly becomes worse, or substantially interferes with daily activities.
For more information about cramps, low blood pressure, nausea, headaches, and fatigue, read Managing Dialysis Side Effects: How to Stay Comfortable and in Control.
How Long Does Hemodialysis Take?
Conventional in-center hemodialysis commonly lasts approximately 3 to 4 hours and is often scheduled three times per week.
The schedule is not the same for everyone. Treatment duration and frequency may depend on:
- Remaining kidney function
- Fluid accumulation
- Laboratory results
- Body size
- Symptoms
- Cardiovascular health
- Treatment tolerance
Home, frequent, and nocturnal hemodialysis programs can use different schedules.
How Does Peritoneal Dialysis Work?
Peritoneal dialysis, or PD, filters blood inside the body using the lining of the abdomen, called the peritoneum, as a filtering membrane.
Sterile dialysis solution enters the abdomen through a soft catheter. While the solution remains inside, waste products move from blood vessels in the peritoneum into the solution.
An osmotic agent in the prescribed dialysis solution—often dextrose and, in some solutions, icodextrin—helps draw extra water across the peritoneal membrane. The used solution carries this fluid and dissolved waste products out of the body when it drains.
PD is generally performed at home or in another clean, private environment after training.
What Happens During a Peritoneal Dialysis Exchange?
Each cycle of draining, filling, and dwelling is called an exchange.
1. Drain
Used dialysis solution flows out of the abdomen through the PD catheter.
The drained fluid should be checked for cloudiness, unusual color, fibrin, or other unexpected changes according to the training provided by the PD team.
2. Fill
Fresh sterile dialysis solution flows into the abdomen through the catheter.
Careful hand hygiene and the connection method taught by the PD program help reduce infection risk.
3. Dwell
The solution remains in the abdomen for a prescribed period called the dwell time.
During the dwell, waste products and extra fluid move across the peritoneal membrane into the dialysis solution. When the dwell ends, the solution is drained and replaced according to the prescription.
Do not independently change the solution, fill volume, dwell time, exchange schedule, or cycler settings.
What Is the Difference Between CAPD and APD?
Continuous Ambulatory Peritoneal Dialysis
Continuous ambulatory peritoneal dialysis, or CAPD, is a form of peritoneal dialysis in which exchanges are performed manually during the day without a dialysis machine.
The exchanges may be completed by the patient or by a trained caregiver.
Many CAPD prescriptions involve approximately three to five exchanges during a 24-hour period, although the exact number and timing depend on the individual prescription.
Each manual drain-and-fill process commonly takes approximately 30 to 40 minutes, followed by a dwell period.
Automated Peritoneal Dialysis
Automated peritoneal dialysis, or APD, is a form of peritoneal dialysis in which a machine called a cycler performs a series of exchanges, usually overnight while the patient sleeps.
The cycler controls:
- When the solution enters
- How much solution is used
- How long it remains
- When it drains
- The sequence of exchanges
Some prescriptions also include solution remaining in the abdomen during the day or an additional daytime exchange.
The PD team programs the cycler and teaches the patient or caregiver how to prepare the equipment, connect safely, respond to alarms, record treatment information, and recognize possible contamination.
| Contact your dialysis team immediately | Seek emergency medical care |
|---|---|
| A missing, much weaker, or clearly changed thrill in a fistula or graft. | Severe chest pain. |
| Cloudy peritoneal dialysis drainage. | Severe difficulty breathing. |
| New or persistent abdominal pain during peritoneal dialysis. | Fainting, confusion, or inability to stay awake. |
| Fever, access redness, increasing warmth, swelling, pain, or drainage. | Heavy or uncontrolled bleeding. |
| Accidental contamination during a peritoneal dialysis exchange. | Severe or rapidly worsening symptoms when the dialysis team cannot be reached. |
| Bleeding that lasts longer than your dialysis team instructed you to expect. | Call 911 or go to the nearest emergency department when symptoms may be life-threatening. |
Why Is Cloudy PD Fluid an Urgent Warning Sign?
Peritonitis is a serious inflammation of the peritoneum, usually caused by an infection in people receiving peritoneal dialysis.
Cloudy drainage, particularly when accompanied by abdominal pain, should be considered possible peritonitis until evaluated.
Call your PD team or its after-hours number immediately. Do not wait until the following day or your next scheduled appointment.
If the team cannot be reached or you have severe pain, repeated vomiting, confusion, breathing difficulty, or rapidly worsening symptoms, seek emergency medical care.
Follow your PD program’s instructions about saving or bringing the cloudy drainage bag for testing.
How Can You Prepare for a Dialysis Session?
Before hemodialysis, follow the instructions provided by the dialysis center regarding meals, medications, clothing, and fluid intake. Arrive on time so the full prescribed treatment can be completed.
Before a PD exchange, prepare the supplies and treatment area exactly as taught. Follow the required hand-hygiene, mask, connection, and contamination procedures.
More detailed planning information is available in Preparing for Dialysis: What to Expect Before You Start.
Fluid and nutrition recommendations are individualized according to laboratory results, remaining urine production, dialysis modality, medications, and nutritional status. Read Dialysis: Daily Habits That Support Your Health for broader lifestyle guidance.
Frequently Asked Questions
How long does a hemodialysis session take?
Conventional in-center hemodialysis commonly takes approximately 3 to 4 hours and is often scheduled three times per week. Home, nocturnal, or more frequent hemodialysis schedules may differ.
Does dialysis hurt?
Needle insertion for hemodialysis may cause brief stinging or pressure. Peritoneal dialysis is generally not painful. Tell your care team about new, severe, or persistent pain.
Can I eat during hemodialysis?
Whether you can eat during treatment depends on your medical condition and the dialysis center’s policy. Follow the instructions provided by your dialysis team.
What should I do if I cannot feel the thrill in my fistula or graft?
Contact your dialysis team immediately. A missing or clearly changed thrill may indicate reduced or blocked blood flow and should not wait until your next treatment.
What should I do if my peritoneal dialysis fluid looks cloudy?
Call your peritoneal dialysis team or its after-hours number immediately. Cloudy drainage may indicate peritonitis. If you cannot reach the team or have severe or rapidly worsening symptoms, seek emergency medical care.
Can I sleep during dialysis?
Automated peritoneal dialysis is designed to perform exchanges while you sleep. Some patients may nap during in-center hemodialysis when permitted. Sleeping during home hemodialysis should occur only as part of a prescribed nocturnal program.
Understanding the Dialysis Process
Dialysis can feel unfamiliar at first, but the steps often become more predictable as you learn the routine and understand what the equipment and clinical team are doing.
The nephrology team at Florida Kidney Physicians can help you prepare for treatment, understand your prescription, and communicate with the dialysis professionals involved in your care. Ask questions and report unexpected symptoms promptly.