Hemodialysis Principles and Practices Flashcards

Which solute transport mechanism in hemodialysis relies on a concentration gradient between blood and dialysate?

Answer: Diffusion

Diffusion is the primary mechanism of solute removal in hemodialysis. Solutes move from an area of higher concentration (blood) to lower concentration (dialysate) across the semipermeable membrane.

What is ultrafiltration in the context of hemodialysis?

Answer: The removal of excess fluid from the blood by applying transmembrane pressure

Ultrafiltration removes excess fluid (water) from a patient's blood using transmembrane pressure (TMP) across the dialyzer membrane. It is controlled by the dialysis machine to achieve the patient's target dry weight.

The dialysate flow rate in a standard hemodialysis session is typically set at:

Answer: 500 mL/min

Standard dialysate flow rate is 500 mL/min, which is approximately twice the blood flow rate (usually 250–350 mL/min). This ratio maintains a favorable concentration gradient for efficient diffusion.

Which type of dialyzer membrane is most commonly used in modern hemodialysis?

Answer: Synthetic high-flux membrane (e.g., polysulfone)

High-flux synthetic membranes such as polysulfone are the current standard. They allow removal of larger middle molecules and have better biocompatibility compared to older cellulose-based membranes.

What is the significance of the blood pump speed in hemodialysis?

Answer: It determines the blood flow rate through the dialyzer, directly affecting solute clearance

The blood pump speed (set in mL/min) determines how fast blood passes through the dialyzer. Higher blood flow rates (Qb) increase solute clearance, particularly for small molecules like urea.

During hemodialysis, why is the dialysate run in a countercurrent direction to blood flow?

Answer: To maintain the maximum concentration gradient along the entire length of the dialyzer, improving efficiency

Countercurrent flow ensures that blood and dialysate always have a concentration difference along the entire membrane, maximizing diffusion efficiency throughout the dialyzer rather than reaching equilibrium early.