Ozonation of blood during extracorporeal circulation. I. Rationale, methodology and preliminary studies

We investigated whether exposure of blood ex-vivo to oxygen-ozone (O-2-O-3) through a gas exchanger is feasible and practical. We first evaluated the classical dialysis-type technique but we soon realized that semipermeable membranes are unsuitable because they are hydrophilic and vulnerable to O-3. We therefore adopted a system with hydrophobic O-3-resistant hollow fibers enclosed in a polycarbonate housing with a membrane area of about 0.5 m(2). First we tested the system with normal saline, determining the production of hydrogen peroxide (H2O2) at O-3 concentrations from 5 to 40 mu g/ml. We then evaluated critical parameters by circulating swine blood in vitro; this revealed that heparin is not an ideal anticoagulant for this system. Finally, we performed several experiments in sheep and defined optimal anticoagulant dose (sodium citrate, ACD), priming solution, Volume of blood flow per min, Volume and concentration of O-2-O-3 mixture flowing counter-current with respect to blood and the time necessary for perfusion in vivo. The biochemical parameters showed that an O-3 concentration as low as 10 mu g/ml is effective this means that gas exchange and O-3 reactivity are rapid and capable of inducing biological effects. The sheep showed no adverse effects even after 50 min of extracorporeal circulation at higher O-3 concentrations (20 to 40 mu g/ml) but the exchanger became less effective (low pO(2) values) due to progressive clogging with cells.