Hemodialysis II: Procedure and Complications

Two large-bore needles are inserted into the patient's fistula or graft. One needle draws blood into the hemodialysis machine while the other returns filtered blood to the patient. Blood flows through tubing into the dialyzer, a cartridge containing thousands of hollow fibers that act as semipermeable membranes. Waste products and excess fluids diffuse out of the blood into dialysate solution, and the filtered blood then returns to the patient through the second needle.

Semipermeable membranes in the dialyzer's hollow fibers allow selective exchange of substances between blood and dialysate. These fibers, made from cellulose or synthetic materials, permit waste products and excess fluids to diffuse out of the blood while retaining essential proteins and blood cells. The membrane's composition and thickness determine the efficiency of waste clearance and fluid removal during treatment.

Heparin is an anticoagulant administered before or at the start of hemodialysis to prevent clot formation. When blood contacts the dialyzer's foreign surface, clotting naturally tends to occur. Heparin inhibits this clotting process, ensuring blood flows smoothly through the machine and tubing without forming dangerous clots that could obstruct the circuit.

After hemodialysis is complete, the needles are removed from the patient's fistula or graft. Firm pressure is then applied to the puncture sites to prevent bleeding and ensure hemostasis, the stopping of blood flow. This pressure application is critical to avoid excessive blood loss and allow the puncture wounds to seal properly.

Most patients undergo hemodialysis for 3 to 4 hours three times weekly at community-based centers. Alternatives include long nighttime hemodialysis, lasting 6 to 8 hours up to six times per week, and short daily hemodialysis, involving 2.5 to 3 hours five to six days weekly, typically performed at home. Schedule selection depends on patient needs and clinical factors.

Hypotension during hemodialysis results from rapid removal of blood volume, reduced cardiac output, and decreased systemic vascular resistance. Symptoms include lightheadedness, nausea, vomiting, seizures, vision disturbances, and chest pain from cardiac ischemia. Treatment involves reducing the volume of fluid removed and administering 0.9% saline solution to stabilize blood pressure.

Muscle cramps during hemodialysis result from hypotension, rapid fluid removal, high ultrafiltration rates, and low sodium dialysate. Risk factors include electrolyte imbalances and hypovolemia. Management involves reducing the ultrafiltration rate and administering fluids such as saline, glucose, or mannitol. Students may explore continuous renal replacement therapy as an alternative renal support modality.