《CRRT管路管理与护理.ppt

* In CRRT therapies, hemodialysis is defined as…. Read the slide. We will discuss dialysate composition a little bit later. It is the dialysate that regulates small molecule clearances. * In the schematic we can see how solutes travel from the high concentration of the blood side into the low concentration of the dialysate side. Dialysate prescription is adjusted to preserve necessary components and remove unwanted metabolites. Note that dialysate flow is established counter-current to the blood flow. This serves to increase effectiveness and maximize clearance. * The third transport mechanism used in CRRT is convection. Convection is defined as…. Read the slide. Water is the solvent and the solutes are “dragged” along with the water as it is removed. Convection also drives adsorption of molecules. Adsorption is: 1. Surface adsorption onto the membrane; 2. Bulk adsorption within the membrane when the molecules can permeate it. The adsorption of solutes onto a membrane occurs as a result of the chemical properties of the membrane. These “adsorptive properties” may be influenced by electrical charge or the affinity of the membrane to “soak up” molecules similar to a sponge soaking up water. Surface adsorption allows for molecules too large to pass through the membrane to be deposited on the surface of the membrane. Bulk adsorption describes the adsorption of molecules that are small enough to pass through the membrane but actually are retained in the structure of the membrane. * To illustrate convection, we go back to the use of the cups. The cup now has a concentrated solution on one side of the semipermeable membrane. As fluid moves (by ultrafiltration), solutes small enough to pass through the pores of the membrane move along with the fluid. Change in blood concentration of a specific solute is dependent on the fluid volume removed. * Now we will begin to explore how the CRRT therapies are applied to the patient to control fluid volumes and