what is Conventional ultrafiltration (CUF)
-a technique that removes plasma water and low molecular weight solutes by a convective process using
transmembrane pressure gradient across a semipermeable membrane
-lvl in reservoir will drop
hemoconcentration is
-an increase in the number of red blood cells resulting from a decrease in plasma
volume
-blood cannot cross the membrane so this is why it just pulls the water molecules and not the RBC
Advantages of
Ultrafiltration/ Hemoconcentration
- Increased protein and red cell concentration
- Removal of inflammatory mediators
- Decreased lung waters
- Improved perioperative hemostasis
- Reduced postoperative ventilatory support
how are Hemoconcentrator Designed
-hollow fiber made up of plastic polymer that doesn’t activate compliment
Ultrafiltration/Hemoconcentration flows
- Blood flow through the fibers (180-200 um in diameter) creates a positive pressure within in the fibers
- Pressure differential between blood side and atmospheric pressure on the ultrafiltrate side of membrane drives water across the membrane
- Microporous membrane – 5-10 um
hollow fiber hemocon
- Blood flow path is inside the fibers
- Effluent path is outside the fibers
- Hemoconcentration involves letting the pressure gradient “push” body water to the effluent side (can be used with or without vacuum)
Ultrafiltration (change in pressure)
•Referred to as convection, is fluid flow through the membrane, forced by a difference in pressure on two sides of the membrane
Diffusion (change in concentration)
• If a higher concentration of a given solute is on one side, then diffusion will try to make the concentrations across the membrane the same.
Achieving filtration across a membrane requires
-blood flow and a pressure gradient
The ability of a solute to be filtered through the membrane depends on what
-the molecular weight compared to the pore size of the filter (sieving coefficient)
The rate of solute removal through the membrane depends on what
-flow rate and transmembrane pressure(TMP)
Transmembrane Pressure (TMP)
• Pressure gradient between blood path and ultrafiltrate compartment
-TMP = (Pin –Pout)/2 + |negative pressure applied to effluent side|
• TMP should not exceed 500 – 600 mmHg
Ultrafiltration Coefficient (Kuf)
•KUF relates the volume removed to pressure applied
Rate of fluid removal depends on
membrane permeability, blood flow, TMP, and hematocrit
•Typical rates are between 2 and 50 ml/hr/mmHg
increase BF and/or TMP does what to rate of fluid removal
increase
decrease in Hct and/or plasma proteins does what to rate of fluid removal
increase
what is Sieving Coefficient and its range
- Represents ease with which a given solute will travel across hemoconcentrator membrane
- Ranges from 0 to 1.0
- A coefficient of 1 means solute will pass the membrane
- A coefficient of 0 means solute will not pass the membrane
will albumin or bilirubin cross the membrane
no
Zero-Balanced Ultrafiltration (Z-BUF)
- Technique that utilizes a hemoconcentrator to maintain controlled EQUALIZED input and output over the CPB pump run
- Ultrafiltrate volume is replaced by an equal amount of a balanced electrolyte solution
reason for using z-buf
- Used to reduce cytokines and complement levels
* Inflammatory markers peak at rewarming so z-buf during rewarming phase
z-buf used to treat
-hyperkalemia
•Need a solution that contains no potassium
•Need to add bicarb
•Monitor sodium levels to avoid hypernatremia
Modified Ultrafiltration (MUF)
• This technique may utilizes the existing cannulas and allows hemoconcentration of the residual circuit contents and then transfused back to patient
• Occurs following termination of CPB
-peds
Where Can Ultrafilters Go?
- Oxygenator recirculation line
* Cardioplegia circuit
using untrafiltration Post-CPB Pump Blood
- Residual pump blood is hemoconcentrated
- Put in bag
- Transfused to patient via the arterial cannula
- Accomplished by creating a small recirculating circuit through the hemoconcentrator
