Hemodialysis I: Introduction

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.

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.

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.

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.

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.

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.

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.