Table of contents
- 1. Introduction
- 2. Principles
- 2.1. Vascular Access
- 3. Methods
- 3.1. Hemofiltration
.
Introduction
- Two basic methods:
- Hemodialysis
- Hemofiltration
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Indications for Renal Replacement Therapy:
1. Uremic Encephalopathy
2. Volume Overload
3. Life Threatening Hyperkalemia
4. Metabolic Acidosis
5. Toxins
Principles
- Hemodialysis removes solutes by diffusion across a semi-permeable membrane.
- Water (fluid) removal is passive (follows solutes as they are removed).
- Removal of solutes is driven by concentration gradient across membrane.
- Concentration gradient decreases as solute concentrations equilibrate, hence both blood and dialysate are moved in opposite directions known as countercurrent exchange.
- Blood moves 200-300 mL/min (2-3x faster than normal GFR)
- Dialysate moves even faster 500-800 mL/min
Vascular Access
- Temporary access can be established by using a large-bore double-lumen catheter in the Internal Jugular or Femoral Veins (subclavian is not advised due to high risk of stenosis)
Methods
Hemofiltration
- Uses hydrostatic pressure gradient to drie fluid through a semi-permeable membrane.
- Small solutes come with the fluid (called solvent drag)
- Can remove large volumes of fluid (3L/h), but solute clearance is poor... therefore must be performed continuously.
- As ultrafiltrate is removed with solutes, another fluid must be given back to the patient to avoid hypovolemia.
- Vascular Access
- In the past: brachial artery and a large vein (IJ or femoral), arterial-to-venous pressure used to drive hemofiltration.
- Now: venovenous hemofiltration, a pump creates filtration pressure.
- Advantages:
- More gradual fluid removal (less hemodynamic compromise)
- Removes larger molecules (including large cytokines in pts with sepsis etc..)
- Disadvantages:
- Must be provided continuously to provide effective dialysis. (time consuming).
- hemodiafiltration (dialysis and hemofiltration -> better for renal failure)
- Requires anticoagulation to keep circut patent.
- Must be provided continuously to provide effective dialysis. (time consuming).
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