Hemodialysis is a treatment that filters your blood through a machine when your kidneys can no longer do the job themselves. It removes waste products, excess salt, and extra fluid that would otherwise build up and become dangerous. Most people on conventional hemodialysis go to a dialysis center three times a week for sessions lasting about four hours each, though home-based and more frequent schedules are also options.
How the Machine Cleans Your Blood
During a session, blood flows from your body through tubing into a device called a dialyzer, sometimes referred to as an artificial kidney. Inside the dialyzer are thousands of tiny hollow fibers made from a semipermeable membrane. Your blood runs through these fibers while a specially prepared fluid called dialysate flows around the outside of them in the opposite direction.
Two physical processes do the heavy lifting. The first is diffusion: waste molecules like urea and creatinine are at high concentrations in your blood and low concentrations in the dialysate, so they naturally move across the membrane into the dialysate and get carried away. The larger the membrane surface area, the more waste gets removed. The second process is ultrafiltration, which uses pressure to push excess water out of your blood and across the membrane. This is how the machine removes the fluid that accumulates between sessions. Larger waste molecules that don’t cross easily by diffusion are primarily removed through this pressure-driven convection.
The dialysate itself is carefully formulated. It contains balanced electrolytes and glucose at concentrations designed to pull the right substances out of your blood while keeping essential minerals at healthy levels.
Vascular Access: How Blood Reaches the Machine
Before hemodialysis can begin, you need a reliable way to move large volumes of blood out of your body and back in again. There are three main types of vascular access, and which one you get depends on timing, your blood vessels, and your overall health.
- Arteriovenous fistula (AV fistula): A surgeon connects an artery directly to a vein, usually in your forearm. This causes the vein to enlarge and strengthen over time, creating a robust access point. It takes at least six weeks to mature before it can be used. Once ready, it should have a blood flow rate of at least 600 ml per minute and a diameter of at least 6 mm. AV fistulas have the lowest infection rates, the fewest hospitalizations, and typically last 3 to 5 years. They’re considered the gold standard.
- AV graft: When your veins aren’t suitable for a fistula, a surgeon uses a synthetic tube to connect an artery to a vein. Grafts can be used sooner than fistulas but generally last only 1 to 2 years and carry higher risks of infection and clotting.
- Central venous catheter: A flexible tube inserted into a large vein in your neck or chest. This is the fastest option and is often used when dialysis needs to start urgently. However, catheters have the highest rates of infection, blood clots, and vein narrowing, so they’re typically a temporary solution.
Planning ahead matters. If you know your kidney function is declining, getting an AV fistula created months before you need dialysis gives it time to mature and avoids the complications that come with a catheter.
What a Typical Session Feels Like
At a dialysis center, you sit or recline in a chair while connected to the machine. A nurse places two needles into your access site (if you have a fistula or graft), one to draw blood out and one to return it. For the next three to four hours, the machine cycles your blood through the dialyzer. You can read, watch TV, sleep, or work on a laptop during this time.
Some people feel fine during treatment. Others experience side effects as fluid and waste are removed. Low blood pressure is the most common issue, and it can come with lightheadedness, nausea, or vomiting. Muscle cramps are also frequent, particularly toward the end of a session, though the exact cause isn’t fully understood. Many people report feeling drained or washed out for several hours afterward.
Common Side Effects
Beyond what happens during individual sessions, hemodialysis carries longer-term side effects that affect daily life:
- Anemia: Failing kidneys produce less of the hormone that stimulates red blood cell production. Hemodialysis itself doesn’t fix this problem, so fatigue from anemia is common and often treated with injections that boost red blood cell counts.
- Itching: Many people experience itchy skin that tends to worsen during or right after treatment. This is related to the buildup of certain substances that dialysis doesn’t fully clear.
- Sleep problems: Restless legs, trouble falling asleep, and disrupted sleep patterns are all reported frequently among people on hemodialysis.
- Cramping and nausea: These tend to be worse if you’ve gained a large amount of fluid between sessions, since the machine has to remove more in the same timeframe.
In-Center vs. Home Hemodialysis
Most people receive hemodialysis at a clinic, but home hemodialysis is a growing option. With proper training (which typically takes several weeks), you or a care partner can operate a home dialysis machine. Home treatment allows more flexibility in scheduling and can be done more frequently or for longer sessions, such as overnight while you sleep.
A Cochrane review of the available evidence found that home hemodialysis may be associated with longer survival, fewer hospital stays, better blood pressure control, and a higher chance of receiving a kidney transplant. People doing dialysis at home also reported shorter recovery times after each session. The certainty of this evidence is still low, partly because the studies used many different ways to measure quality of life, making direct comparisons difficult. Still, the trend consistently favors home treatment for people who are able and willing to manage it.
How Doctors Measure Treatment Quality
Not all dialysis sessions are equally effective. Doctors track how well each session cleans your blood using a metric called Kt/V, which factors in the dialyzer’s clearing ability, treatment time, and your body size. National Kidney Foundation guidelines recommend a minimum Kt/V of 1.2 per session for people on a three-times-per-week schedule. Below that threshold, studies have linked lower clearance to increased mortality.
A simpler measure is the urea reduction ratio (URR), which compares the level of urea in your blood before and after treatment. It’s expressed as a percentage: the higher the number, the more waste was removed. If your numbers consistently fall short, your care team may extend session times, adjust the dialyzer, or investigate access problems.
Diet and Fluid on Hemodialysis
Your kidneys normally handle excess sodium, potassium, phosphorus, and fluid around the clock. Hemodialysis only runs a few hours at a time, so what you eat and drink between sessions directly affects how you feel and how safe treatment is.
Sodium intake should stay below 2,300 milligrams per day, roughly one teaspoon of table salt. Excess sodium makes you thirsty, leading to more fluid intake between sessions, which means more fluid the machine has to pull off (and more cramping and blood pressure drops during treatment). Potassium and phosphorus limits are individualized based on your blood work, but both require attention. Too much potassium between sessions can cause dangerous heart rhythms, and excess phosphorus pulls calcium from your bones over time.
Fluid limits are often the hardest adjustment. Because your kidneys may produce little or no urine, every glass of water, cup of coffee, or bowl of soup adds fluid that stays in your body until the next session. Your dietitian will set a daily fluid target based on your urine output and weight gain between treatments.
Life Expectancy and Long-Term Outlook
Hemodialysis is a life-sustaining treatment, not a cure. It replaces only part of what healthy kidneys do, filtering waste and fluid but not fully restoring hormone production or other kidney functions. How long someone lives on dialysis depends heavily on age, the underlying cause of kidney failure, and other health conditions like diabetes or heart disease.
For many people, hemodialysis serves as a bridge to a kidney transplant, which generally offers better long-term survival and quality of life. For others, it becomes a long-term treatment. Either way, staying consistent with your treatment schedule, managing your diet, and keeping your vascular access healthy are the factors most within your control that influence how well you do.