CRRT PRINCIPLESADEL MUSBAH AWAJEH RN BSN MSC

MOLECUL TRANSPORTION MECHANISM

ULTRAFILTRATIONDIFFUSIONCONVECTIONADSORPTION

ULTRAFILTRATIONHOW ultrafiltration works:- On the blood side of the hemofilter you have a positive pressure gradient. on the fluid side of the hemofilter you have a negative pressure gradient. The effluent pump applies pressure on the membrane causing the fluid to move from the positive pressure gradient to the lower pressure gradient .

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DIFFUSION.

Example, let us assume the blood in the

filter has a high concentration of potassium molecules and on the fluid/dialysate compartment has a low concentration of potassium. The potassium gradually diffuses through the membrane from the area of a higher potassium concentration to the area of a lower potassium concentration

until it is evenly distributed .

AdsorptionAdsorption is the removal of solutes from the blood because they cling to the membrane.

Think of an air filter. As the air passes through it, impurities cling to the filter itself.

Eventually the impurities will clog the filter and it will need to be changed .

The same is true in blood purification. High levels of adsorption can cause filters to clog and become ineffective

PRINCIPLES OF CRRT

CRRT clearance of solute is dependent on the following:The molecule size of the soluteThe pore size of the semi-permeable membrane The higher the ultrafiltration rate (UFR), the greater the solute clearance

PRINCIPLES OF CRRTSmall molecules easily pass through a membrane driven by diffusion and convection.Middle and large size molecules are cleared primarily by convection .Semi-permeable membrane remove solutes with a molecular weight of up to 50,000 Daltons.Plasma proteins or substances highly protein—bound will not be cleared .