Hemoconcentration
Hemofiltration
Diafiltration
Ultrafiltration
CAVH
CAVH D
Hemofiltration Structure
and Function
 Glorified sieve
Molecules move across
according to size (molecular
wt.)
Plasma binding
Transmembrane pressure
(TMP)
Hemofilters vs Dialysis
Dialysis
Semipermeable membrane
Concentration gradient (osmosis)
Conductive exchange of solutes
Dialysate
Some convective force
Molecular Clearance
Dialysis Vs.
Hemofiltration
Conventional Dialysis on
ECMO
Conventional Dialysis on ECMO
is performed by accessing the
circuit by stopcocks, taking
blood from the arterial side of
the circuit and returning it to
the venous side or into a venous
access line in the patient.
Dialysis Service controls solute
and fluid removal rates.
Dialysis blood flow rates vary
with size of patient and access.
Hemofiltration Rate
Blood Flow
TMP = (P in + P out)/2 + vacuum
on HF side, ex (120+100)/2
=110+(-75) = 185 mmHg
Hematocrit
Protein concentration
Resists fluid removal
Blood Viscosity
Temperature
Hemofiltration Rates Vs
Blood Flow
Minifilter for ECMO
10 cm plastic tube
Contains 25 Polysulfone hollow
fiber (exchange membrane)
Primes with 6 ml. (150cm2)
TMP 500 mmHg
Blood flow 500ml/min
Molecular Cut Off
Device acts as a sieve
Solutes (molecules) dissolved in
plasma are either retained or
removed according to their size
(molecular Wt. MW)
MW cut off 50,000 daltons
Electrolytes 75-240 daltons
Therapeutic drugs 6,00020,0000 daltons
Note - Dalton is unit of atomic
Wt. 1Da = 1.66X10-24
Solute Clearance
Solutes in hemofiltrate are in
the same concentration as the
pts. Blood (if below the MW cut
off)
The amount removed is equal to
the hemofiltration rate time the
concentration of solute in
question in the filtrate
 Amount removed = (Concentration in
filtrate) X (HR)
Solute Clearance
If large amounts of volume
are removed with
Hemofiltration, the actual
amount of a given solute
removed from a baby may
be substantial
Solute Clearance
While the concentration of a
solute in the HF may not be
known, its concentration in the
blood is routinely measured.
 Ex. Sodium. 134 mEq/l
If the MW is below the cut off of
the fiber the concentration in
the HF is essentially the same
as the blood. Then: amount
removed = (Conc.in blood) X (HF Rate)
Sieving Coefficient
SC - The ratio of the amount of
a given solute in the UF to that
amount in the Blood.
Ex 1. Sodium - amount in UF is 135
mEq/L and amount in the blood is 135
mEq/L the Sieving Coef. is 1.0.
Ex 2. Albumin Serum = 5 gm/dl Blood
Albumin UF = 0 gm/dl SC = ?
Other large molecules:
 Total Bilirubin - 0.03, erythromycin0.37, calcium - 0.64
Sieving Coefficients for
Selected Molecules
Sieving Coefficient &
Protein Binding
Calculation of Solute clearance
is complicated if molecule is
protein bound. Monitoring of
medication blood level is
advised when aggressive HF is
used.
Protein binding data is available
for many medication used
during ECMO.
Calculating Solute
Clearance
It turns out to be easier to
calculate the amount of a
substance being removed if
you know its Sieving
Coefficient using:
Amount lost =
(Conc. In blood) X (SC) X (HR)
Dialysis With
Hemofiltration
Dialysate solution may be used
on the Hemofiltrate side of the
cartridge to the remove solutes
by osmotic gradients
(conduction) and
filtration(convection).
Concentration of molecules in
Dialysate control removal of
various solutes from the blood.
Ex. If Potassium is high in blood
Dialysate will be low in
Potassium the rest of the
molecules will be balanced.