Hemodialysis is a medical treatment that filters your blood through a machine when your kidneys can no longer do the job on their own. It removes waste products, excess fluid, and balances electrolytes, essentially performing the critical functions your kidneys have lost. Most people on hemodialysis go to a dialysis center three times a week for sessions lasting three to four hours each, though home-based options exist with different schedules.
How the Filtering Process Works
The core of a hemodialysis machine is a component called a dialyzer, sometimes referred to as an artificial kidney. Inside it, your blood flows along one side of a semipermeable membrane while a specially mixed cleaning solution called dialysate flows along the other side. Waste products and excess substances in your blood move across the membrane into the dialysate through diffusion, the same natural process that causes a tea bag to steep in hot water. Substances travel from the side where they’re more concentrated to the side where they’re less concentrated.
The dialysate is carefully formulated to pull the right things out of your blood while keeping what you need. It contains six key electrolytes: sodium, potassium, calcium, magnesium, chloride, and bicarbonate, plus a small amount of glucose. The concentrations are deliberately set to create the right gradients. Bicarbonate, for example, is kept higher than normal blood levels because people with kidney failure tend to have too much acid in their blood, and this helps correct the imbalance. Potassium and phosphorus concentrations are set lower than blood levels so those substances flow out.
The machine also removes excess fluid from your blood through a pressure difference across the membrane. This is especially important because people whose kidneys aren’t working tend to retain fluid between sessions, which can strain the heart and lungs.
Vascular Access: How Blood Reaches the Machine
For hemodialysis to work, a reliable way to move large volumes of blood out of your body and back in is essential. There are three types of vascular access, and each has different tradeoffs.
An arteriovenous (AV) fistula is considered the gold standard. A surgeon connects an artery directly to a vein, usually in the forearm, which causes the vein to grow larger and stronger over time. The catch is that a fistula needs two to three months to mature before it can be used. Once it’s ready, though, it has the lowest rates of infection and clotting of all three options.
An AV graft uses a synthetic tube to connect an artery and vein. It’s ready for use in about two to three weeks, making it faster than a fistula. However, grafts are more prone to infection and blood clots. Repeated clotting can eventually block the graft entirely.
A venous catheter is a tube inserted into a large vein, typically in the neck. It works immediately, which makes it the go-to option when someone needs to start dialysis urgently. It also carries the highest risk of infection, clotting, and vein scarring. For these reasons, catheters are generally used as a short-term bridge while a fistula or graft is being prepared.
What a Typical Session Feels Like
In-center hemodialysis follows a predictable rhythm: three sessions per week, each lasting roughly three to four hours. You sit or recline in a chair while the machine does its work. Many people read, watch TV, nap, or use a laptop during treatment. Nurses monitor your vitals throughout the session.
A drop in blood pressure is the most common side effect during treatment. When excess fluid is pulled from your body, especially if you’ve gained a significant amount of fluid between sessions, your blood pressure can fall. This may bring on shortness of breath, nausea, vomiting, or abdominal cramps. Muscle cramps during treatment are also common, though the exact cause isn’t fully understood.
These side effects tend to be more pronounced when more fluid needs to be removed in a single session, which is one reason sticking to fluid limits between treatments matters so much.
Home Hemodialysis Options
Not everyone needs to travel to a center. Home hemodialysis comes in several formats. Conventional home hemodialysis mirrors the center schedule: three sessions a week, three to four hours each. Short daily home hemodialysis involves five to seven sessions per week, with each one lasting about two hours. Nocturnal home hemodialysis runs while you sleep, typically six nights a week or every other night, with treatments lasting six to eight hours.
More frequent or longer sessions can be gentler on the body because fluid and waste removal happens more gradually. The tradeoff is the commitment of training (which takes several weeks), maintaining a supply of equipment at home, and having a care partner available in many cases.
Safety Systems Inside the Machine
Modern dialysis machines include multiple layers of safety monitoring. Pressure sensors track blood pressure on both the outgoing and returning lines, detecting any obstructions immediately. Ultrasonic air detectors scan the blood tubing for air bubbles without touching the blood itself. If a significant air bubble is detected, the machine can trap it or stop the process entirely. Additional sensors watch for blood leaks in the dialysate circuit. These automated systems run continuously throughout every treatment session.
Dietary Changes on Hemodialysis
Because dialysis only happens a few times a week rather than continuously like healthy kidneys, what you eat and drink between sessions directly affects how you feel during treatment. Your renal dietitian will set personalized targets, but the general principles are consistent.
Potassium needs to be limited because dangerous buildups between sessions can affect your heart rhythm. That means cutting back on potassium-rich foods like bananas, avocados, kiwis, and dried fruit, and choosing lower-potassium alternatives. Small portions of higher-potassium foods are sometimes fine, like a couple of cherry tomatoes on a salad, but quantities matter.
Phosphorus is another mineral to watch. Healthy kidneys filter it constantly, but dialysis can’t keep up with a high-phosphorus diet. A common guideline is limiting milk to half a cup per day, since dairy is a major source. Many people on hemodialysis also take phosphorus binders with meals.
Fluid restriction is often the hardest adjustment. Every ounce of fluid you take in between sessions has to be removed during your next treatment. The more fluid that needs to come off, the more likely you are to experience cramping and low blood pressure. Your dietitian will help you set a daily fluid goal and track intake, which includes not just drinks but also foods with high water content like soups, ice cream, and certain fruits.
Medicare Coverage for Dialysis
In the United States, kidney failure qualifies you for Medicare regardless of your age, provided you or a qualifying family member has a sufficient work history under Social Security or the Railroad Retirement Board. This is one of the few conditions that triggers Medicare eligibility independent of age.
If you already have private insurance when you start dialysis, a 30-month coordination period applies. During that time, your private plan pays first and Medicare covers remaining costs as the secondary payer. After 30 months, Medicare typically becomes your primary coverage. The specifics of what you owe out of pocket depend on the type of Medicare plan you’re enrolled in.