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Hemodialysis I: Introduction
Hemodialysis (HD) is a medical treatment that artificially removes waste products, excess fluids, and toxins from the blood when the kidneys are no lo…
Hemodialysis filters waste, excess fluids, and toxins from the blood using a semipermeable membrane in a dialyzer while preserving essential components like blood cells.
It requires vascular access to allow rapid blood flow, usually achieved through an arteriovenous fistula or AVF.
AVF is surgically created by connecting an artery, such as the radial or brachial artery, to a vein, typically the cephalic or basilic vein.
This connection makes the vein enlarge and strengthen, a process called maturation, which usually takes 6 to 12 weeks.
Once the AVF has matured, two large-bore needles, usually 14 to 16 gauge, are inserted into the vein during dialysis to allow blood to flow in and out of the body.
If an AVF cannot be created due to vascular issues, such as peripheral vascular disease, an arteriovenous graft, or AVG, may be used.
AVGs are synthetic polytetrafluoroethylene tubes surgically placed beneath the skin to attach an artery to a vein.
They can be used within 2 to 4 weeks but carry a higher risk of complications, like infection and thrombosis.
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Q1: What is hemodialysis and how does it work?
Hemodialysis is a medical treatment that removes waste products, excess fluids, and toxins from the blood when kidneys fail. Blood is filtered through a semipermeable membrane inside a device called a dialyzer. Harmful substances diffuse across the membrane into a cleansing solution called dialysate, while essential components like blood cells and proteins are preserved and returned to the body.
Q2: Why is vascular access important for hemodialysis?
Hemodialysis requires rapid blood flow to effectively filter waste and excess fluids. Vascular access allows blood to be diverted from the patient's circulation to the dialysis machine and back. Without adequate vascular access through large blood vessels, the treatment cannot deliver sufficient blood flow rates needed for effective waste removal and fluid balance restoration.
Q3: What is an arteriovenous fistula and how is it created?
An arteriovenous fistula (AVF) is the preferred permanent vascular access for hemodialysis. It is surgically created by connecting an artery, such as the radial or brachial artery, directly to a vein, typically the cephalic or basilic vein. This connection causes the vein to enlarge and strengthen through a process called maturation, which usually takes 6 to 12 weeks before the fistula can accommodate two large-bore needles for dialysis.
Q4: How can patients promote arteriovenous fistula maturation?
Patients can perform hand exercises, such as squeezing a rubber ball, to promote vein dilation and speed up the maturation process of an arteriovenous fistula. These exercises increase blood flow through the fistula, encouraging the vein to enlarge and strengthen more rapidly. A properly functioning AVF produces a thrill (buzzing sensation) and a bruit (rushing sound) that indicate high-velocity blood flow.
Q5: What is an arteriovenous graft and when is it used?
An arteriovenous graft (AVG) is a synthetic alternative to an arteriovenous fistula, made from polytetrafluoroethylene (PTFE) and surgically placed under the skin to connect an artery to a vein. AVGs are used when patients have compromised vascular systems or veins unsuitable for fistula creation. They can be used within 2 to 4 weeks but carry higher risks of complications like infection and thrombosis compared to AVFs.
Q6: What are the main complications associated with arteriovenous grafts?
Arteriovenous grafts are prone to serious complications including infections, thrombosis (clotting), and central venous stenosis (CVS), which is narrowing of central veins that impedes blood flow to the heart. Because AVGs are synthetic, infections are difficult to treat and often require surgical graft removal. CVS progression can lead to loss of vascular access for hemodialysis, making it a significant clinical concern.
Q7: How does hemodialysis differ from other renal replacement therapies?
Hemodialysis uses a semipermeable membrane in an external dialyzer to filter blood outside the body, requiring vascular access and a dialysis machine. In contrast, peritoneal dialysis uses the patient's peritoneal membrane inside the abdomen as the filtering surface. For patients considering long-term renal replacement options, understanding hemodialysis procedure and complications alongside alternatives like peritoneal dialysis helps inform treatment decisions.