Ultrafiltration Flashcards
Conventional Ultrafiltration (CUF)
is a technique that removes plasma water and low molecular weight solutes by a convective process using hydrostatic pressure forces across a semipermeable membrane.
Zero Balance Ultrafiltration (ZBUF)
is a technique utilizing an hemoconcentrator to maintain a controlled EQUALIZED input and output over the CPB pump run
Slow Continuous Ultrafiltration (SCUF)
s a technique utilizing a slow, steady ultrafiltration during the CPB pump run
Modified Ultrafiltration (MUF)
is ultrafiltration occurring after the separation from CPB.
the Effluent path first concepts related to the use of ultrafiltration in hospital practice, date from
1928
Ultrafiltration is achieved
(using a hemoconcentrator) in the CPB circuit and allows the filtration of body water across a semi-permeable membrane utilizing a hydrostatic pressure gradient
Blood flow path is
inside the fibers. (higher pressure)
Effluent path
is outside the fibers
uses pressure gradient to
push crap from blood to effluent side. is outside the fibers
Dialysis will use a dialysate solution on the
effluent side to control precise solute excretion
HOW DO ULTRAFILTERS WORK?
Diffusion (change in concentration)
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
osmosis in dialysis
this refers not to water movement across the hemodialyzer membrane, but across cell membranes
Achieving filtration across a membrane requires
blood flow and hydrostatic (pressure gradient)
Pressure /flow and resistance is key
The ability of a solute to be filtered through the membrane depends on
the molecular weight compared to the pore size of the filter (sieving coefficient)
he rate of solute removal through the membrane depends
on the flow rate and transmembrane pressure (TMP)
A dalton quanitates mass, defined as
/12 the mass of a carbon-12 nucleus. It’s also called the atomic mass unit, abbreviated as either “amu” or “u”. You can convert kg into u using this conversion factor:
1 u = 1.6605655(86) × 10-27 kg
BOTTOM LINE: very, very small
Removing body water will allow
an elevation in the Hct without transfusion
This is what you can do when you have extra volume in your reservoir. Can be combined with other procedures and will become CUF, SCUF, Z-BUF, MUF.
Sieving Coefficient
Ratio of blood solute concentration to plasma concentration
Ranges from 0 to 1.0 A coefficient of 1 means the solute concentrations
equilibrate on both sides of the membrane
A coefficient of 0 means no solute passed the membrane (large molecular weight/size)
ca Sieving Coefficient
.55
k Sieving Coefficient
1.0
mg Sieving Coefficient
1.0
aprotinin Sieving Coefficient
1.0
digoxin Sieving Coefficient
.75
fentanyl Sieving Coefficient
.28
furosemide Sieving Coefficient
.05
heparin Sieving Coefficient
.20
midazolam Sieving Coefficient
.06
pancuronium Sieving Coefficient
.13
Diffusion in dialysis
movement of solutes from a area in which they are in high concentration to one of a lower concentration – along an electrochemical gradient. An electrolyte solution runs countercurrent to blood flowing on the other side of the membrane. Small molecules such as urea move along the into the dialysate fluid. Larger molecules are poorly removed by this process. Solute removal is directly proportional to the dialysate flow rate
when effluent becomes pink
you are breaking up RBC
Convection / ultrafiltration – solute is carried
(in solution) across a semipermeable membrane in response to a transmembrane pressure gradient
a process known as solvent drag
solvent drag mimics
what actually happens in the normal human kidney. The rate of ultrafiltration depends upon the porosity of the membrane, and the hydrostatic pressure of the blood.
ultrafiltration is very effective
in removal of fluid and middle-sized molecules, which are thought to cause uremia. Moreover, most of the cytokines involved in sepsis are “middle molecules”
Transmembrane Pressure is the
the pressure across the filter capillary tubes
pore size is the
molecular weight cut off the filter is designed for (in Daltons)
Transmembrane pressure is NOT
pressure drop
TMP=
Filter P(in) + Return P(out)/2 + [Vacuum] OR Filter P(in) + Return P(out)/2 - EFFLUENT PRESSURE
as you increase flow of blood you increase
rate of removal and transmembrane pressure
Conventional Ultrafiltration (CUF)
Technique that utilizes a hemoconcentrator to remove plasma water and low molecular weight solutes by a convective process using hydrostatic pressure forces across a semipermeable membrane
cuf improves potential
for increasing adequate oxygen delivery to tissue (increases Hct)
cuf draws in
extravascular fluid Your level in the venous reservoir will drop
Slow Continuous Ultrafiltration (SCUF)
a technique utilizing a hemoconcentrator for a slow, steady ultrafiltration during the CPB pump run
Slow rate over longer time
Zero Balance Ultrafiltration (ZBUF)
is a technique utilizing an hemoconcentrator to maintain a controlled EQUALIZED input and output over the CPB pump run
IN = OUT
Modified Ultrafiltration (MUF)
is ultrafiltration occurring after the separation from CPB.
This technique may utilize the existing cannulas and allows concentration of the circuit contents to be hemoconcentrated (allows post-op reduction in total body water)
Considered a “standard of care” in pediatrics
WHERE CAN ULTRAFILTERS GO IN THE CARDIOPULMONARY BYPASS CIRCUIT?
Oxygenator Recirculation Line Purge Line Sampling Manifold Cardioplegia Circuit
MONITORING ULTRAFILTRATION
3 main parameters are critical:
Flow Pressure Volume
The blood flow through the ultrafilter should be
monitored, it will be easier to control when a roller pump is used exclusively for the ultrafilter.
hen the blood to the ultrafilter is removed directly from the arterial line, flow depends on
the characteristics of the ultrafilter and may be reduced by partially clamping the inlet
In general, negative pressures (vacuum)
of 100 to 200 mmHg may be applied
So, greater ultrafiltration can be achieved by:
increasing theTMP partially clamping the outlet line of the
ultrafilter
increasing in vacuum applied to the external surface of the membranes.
WHAT ARE THE PHYSIOLOGICAL EFFECTS OF ULTRAFILTRATION?
CPB causes increased capillary permeability, including the systemic inflammatory reaction triggered by CPB
Capillary permeability propitiates an increase in the total body water
This increase of the extravascular fluid affects the functions of the major organs.
ULTRAFILTRATION AND SYSTEMIC INFLAMMATORY REACTION -ORGANS
LUNGS: Pulmonary edema may reduce the efficiency of gas exchange and pulmonary complacency.
HEART: Myocardial edema may affect ventricular function making (diastolic filling difficult and reducing the efficiency of systole)
BRAIN: Cerebral edema may have serious consequences.
KIDNEY: Renal function may also be impaired and the renal immaturity may make elimination of liquids more difficult.
The most severe systemic inflammatory response may manifest as multiple system organ failure (MSOF)
ULTRAFILTRATION AND SYSTEMIC INFLAMMATORY REACTION-
CPB activates the leucocytes and several proteic systems of the plasma.
Activation results in the production of a large number of cytokines, complement fractions and vasoactive substances.
The main pro-inflammatory cytokines are tumor necrosis alpha factor and the IL-1 beta, IL-6 and IL-8 interleukins. The residues of the activation of complement system is the activation of C3a and C5a
ultrafiltration also limits
inflammatory mediators
Things to be wary of…..
When you filter you are losing volume- watch your level
Pink effluent is often a result of too high TMP Vacuum will increase effluent and increase
hemolysis – more is not necessarily better
Hemoconcentration is usually a shunt – it must be off if the pump is off (compensate for it)
