HEpatic Regeneration With COupled Plasma Filtration and Adsorption for Liver Extracorporeal Detoxification

CPFA allows an improvement of blood pressure and inflammatory response during sepsis and multiorgan failure. This extracorporeal detoxification system was developed to non-specifically remove larger mediators during systemic inflammation with an extracorporeal circuit consisting of a plasma filter, a resin cartridge and a high-flux dialyzer. At present it is performed with the use of a five-pump modular treatment consisting of a plasma filter and a following absorption on an unselective hydrophobic resin cartridge and a final passage of the reconstituted blood through a high permeability polyethersulfone haemofilter, in which convective exchanges may be applied in a postdilution mode. Ronco et al. in 2002 compared CPFA treatment to continuous veno-venous haemodiafiltration (CVVHDF) in 10 patients affected by septic shock. The patients underwent 10-hour length CPFA and an increase of arterial blood pressure and a significant reduction of norepinephrine dosage were observed in comparison to the arterial blood pressure and the norepinephrine dosage achieved with the CVVHDF treatment. Formica et al. in 2004 confirmed these results using 100 CPFA treatments in 12 patients affected by septic shock with or without acute kidney injury. Patient survival at 28 days was 90%, while survival of after 90 days was 70%. Mao et al. also compared CPFA with High Volume Hemofiltration and they showed that CPFA increased the ratio between anti-inflammatory and pro-inflammatory cytokines; CPFA enhanced Human Leucocyte Antigen (HLA) class II expression on monocytes and improved the leukocyte response to inflammation measuring leukocyte production of Tumor Necrosis Factor-alfa. Recently Livigni et al. on behalf of the Italian group for the evaluation of interventions in intensive care medicine carried out a randomised controlled trial enrolled 330 adult patients with septic shock, 192 were randomised to either have CPFA added to the standard care, or not. CPFA was to be performed daily for 5 days, lasting at least 10 h/day. The trial was stopped because nearly 50% of the patients could not achieve treatment completion due to technical reasons (primarily coagulation). The trial did observe that patients with the highest amounts of treated plasma appeared to have a survival benefit. The technique underwent further modifications to improve the technical aspects and anticoagulation and a new trial is now underway with a high dose of plasma > 0.18 litres/ kg/ day.

As to the hepatic toxin removal it depends on the ability of the detoxification system to extract albumin bound toxins by means of adsorption. The adsorption consists in the consolidation on the surface of a solid material of molecules floating in a fluid after matching the fluid with the solid. The consolidation is due to weak bounds as in the case of Van der Waals and hydrophobic bounds. The selectivity of adsorption occurs when albumin molecules easily pass throughout the sorbent while the sorbent draw the albumin carried toxins into the pores of the sorbent. The hepatic toxins often are hydrophobic and with molecular weight < 1,000 daltons (bilirubin = 406 daltons, cholic acid = 283 daltons, chenodeoxycholic acid = 272 daltons). The albumin structure consists in 3 domains, which allows a multi-binding protein transport. As to bilirubin, its protein binding is a physiological protective mechanism to prevent the free bilirubin diffusion and toxicity in human tissues. The amount of bilirubin production is about 300 gr/day. The molecule most tightly bound to albumin is non-conjugated bilirubin: the amount of non-conjugated bilirubin not bound to albumin is < 0.1%. Non-conjugated bilirubin is currently considered as "indirect" bilirubin because it gives an indirect reaction with standard diazo reagents. Conjugated bilirubin is also bound to albumin but with a reduced affinity. The albumin-bilirubin bond occurs by means of covalent or non-covalent strengths. The 2 bilirubin binding sites on albumin show different constant of association (Ka). The primary site has a high affinity, its Ka is 55-68 micromol/L and it can bind only 1 mole of bilirubin. The secondary site has a low affinity, its Ka is 4.4-5.0 micromol/L and it can bind more than 1 mole of bilirubin. A gap between 20 and 50 ångström between albumin and the sorbent is needed to move bilirubin from albumin to the sorbent.

The CPFA efficacy on bilirubin adsorption is based on hydrophobic polystyrene-divinylbenzene copolymer matrices of the resin cartridge that have mean pore sizes of 30 nanometres. Harm et al. reported that the hydrophobic polystyrene-divinylbenzene copolymer of CPFA resin cartridge (type B copolymer: mean diameter 128 micron, pore size 30 nanometres and surface area of 700 m2/gr of resin) binds higher amount of bilirubin than the amount of bilirubin bound with the other kinds of polystyrene-divinylbenzene copolymer matrices tested (type A copolymer: mean diameter 120 micron, pore size 15 nanometres and surface area of 900 m2/gr of resin; type C copolymer: mean diameter 37 micron, pore size 100 nanometres and surface area of 200 m2/gr of resin).

Few authors in vivo assessed the bilirubin adsorbing ability of the neutral styrenic resin of CPFA. Caroleo et al. reported the first case of hepatic toxins removal by means of CPFA in a patient affected by acute liver failure due to cardiogenic shock. Maggi et al. reported 2 further cases where bilirubin removal was obtained in 2 patients with delayed graft function after liver transplantation. The patients achieved a 40% bilirubin reduction after 3 treatments with CPFA lasting 3-hours each.