Hemodialysis
Hemodialysis (HD) is a form of RRT that involves the removal of undesired
solutes from the blood after it is passed through an “artificial kidney” or dialyzer.
To understand how HD works, let’s define some basic terms:
- Hemofiltration
Hemofiltration is the process of clearing blood of metabolic waste by the
passage of blood through a semi permeable filter or membrane. - Convection
During convection, hydrostatic pressure “forces” water and solutes to pass
through a filtration membrane (hemofilter), including small and large
molecules. The hemofilter is impermeable to proteins and cells due to the
small size of its pores. - Diffusion
Is the mechanism by which, solutes are transported across the filtration
membrane in direction to a concentration gradient. Solutes move or
“diffuse” to the side of the membrane that has lower concentration of that
solute. Diffusion is effective in clearing small molecules such as potassium
and urea but ineffective for larger solutes or albumin (LMW proteins). - Adsorption
It is the mechanism by which non-desired molecules are adhered to the
dialyzer membrane. - Molecule size
a. Small molecules. <500 Daltons. Most electrolytes, creatinine and urea