Hemodialysis Goals and Transport Principles
Key Takeaways
- Diffusion moves solutes from higher concentration to lower concentration across the dialyzer membrane.
- Ultrafiltration removes plasma water by a pressure gradient across the membrane.
- Convection occurs when solutes are carried with water movement during ultrafiltration.
- Technicians set and monitor treatment according to the prescription and escalate alarms or mismatches.
The dialyzer as the exchange site
Blood and dialysate flow on opposite sides of a semipermeable membrane inside the dialyzer. Cells and large proteins stay in the blood compartment, while smaller solutes and water can move according to concentration and pressure gradients.
Core principles
| Principle | What moves | Main driver | Exam cue |
|---|---|---|---|
| Diffusion | Solutes such as urea and potassium | Concentration gradient | Waste moves from blood toward dialysate when dialysate concentration is lower. |
| Osmosis | Water | Solute concentration difference | Water tends to move toward the side with higher solute concentration. |
| Ultrafiltration | Water | Pressure gradient | Ordered fluid removal is achieved through transmembrane pressure and machine control. |
| Convection | Water plus dragged solutes | Water movement | Solutes are carried along as water is removed. |
The treatment goal is not just to run blood through tubing. The machine, dialyzer, dialysate, blood flow, treatment time, and prescribed UF goal work together to remove wastes and excess water safely.
A CCHT sets the machine according to the prescription, checks required parameters, monitors alarms and pressures, and reports mismatches. Changing dialysate, treatment time, or fluid goals independently is outside the technician role.
Which transport principle best explains urea moving from the patient's blood into dialysate across the dialyzer membrane?
The calculated UF goal appears much higher than expected from the patient's weight and prescription. What should the technician do?
Which statement describes convection during hemodialysis?