26.6: Hemodialysis II: Procedure and Complications

Dialyzers

A hemodialysis (HD) dialyzer is a plastic cartridge containing thousands of parallel hollow fibers, which serve as semipermeable membranes. These fibers are typically made from cellulose-based or other synthetic materials. During HD, blood is pumped into the top of the cartridge and distributed among these fibers. Simultaneously, dialysis fluid, known as dialysate, is introduced into the bottom of the cartridge, bathing the outside of the fibers. Across the semipermeable membrane, processes like ultrafiltration, diffusion, and osmosis facilitate the exchange of waste products and fluids. Once the blood has been filtered, it converges at the end of the fibers into a single tube that returns it to the patient. Dialyzers vary in surface area, membrane composition and thickness, and efficiency in clearing waste products and excess fluid.

Procedure for Hemodialysis

Large-bore needles, typically 14 to 16 gauge, are used for vascular access during HD. These needles are inserted into a patient’s fistula or graft. One needle draws blood from the patient into the HD machine, while the other returns the filtered blood to the patient. The needles are connected to dialysis tubing, forming a circuit with the machine. The needle closer to the patient’s fistula or the red catheter lumen pulls blood toward the dialyzer using a blood pump.

In contrast, the blue catheter lumen returns the dialyzed blood. When blood interacts with the dialyzer's foreign surface, clotting tends to occur. To mitigate this, heparin is administered as an anticoagulant. Once the dialysis session is complete, the needles are removed, and firm pressure is applied to the puncture sites to prevent bleeding until hemostasis is achieved.

Settings and Schedules for Hemodialysis

Most HD patients receive treatment at community-based centers, typically undergoing dialysis for 3 to 4 hours three times a week. Other scheduling options include short daily HD and long nighttime HD. Long nighttime sessions last 6 to 8 hours and can occur up to six times weekly. Daily HD involves about 2.5 to 3 hours, 5 to 6 days per week, and is generally performed at home.

Complications of Hemodialysis

• Hypotension: Hypotension during HD can result from rapid removal of blood volume (hypovolemia), reduced cardiac output, and decreased systemic vascular resistance. Symptoms may include lightheadedness, nausea, vomiting, seizures, vision disturbances, and chest pain due to cardiac ischemia. Treatment typically involves reducing the volume of fluid removed and administering a 0.9% saline solution to stabilize blood pressure.
• Muscle Cramps: Factors that increase the risk of muscle cramps during HD include hypotension, hypovolemia, high ultrafiltration rate (UFR), and low sodium dialysate. Reducing the UFR and administering fluids such as saline, glucose, or mannitol can alleviate muscle cramps.
• Blood Loss: Blood loss may occur when blood is not completely flushed from the dialyzer, accidental blood tubing disconnection, or dialysis membrane rupture. Additionally, bleeding can happen at the needle site after HD, mainly if excessive heparin is used or if the patient has underlying clotting disorders.
• Hepatitis: Transmission of hepatitis B in dialysis settings remains possible, often due to lapses in infection control practices. To prevent transmission, all patients and staff in dialysis units are vaccinated against hepatitis B.