Hemofiltration Diafiltration Ultrafiltration CAVH CAVH D 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 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 6,000-20,0000 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, erythromycin- 0.37, 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.