Long Term Evaluation of Gas Exchange and Hydrodynamic Performance of a Heparinized Artificial Lung: Comparison of Two Different Hollow Fiber Pore Sizes

Abstract

We compared the performance of a heparinized hollow fiber artificial lung (Medtronic, Minimax) featuring standard hollow fibers (Group A) and experimental hollow fibers with a smaller pore size (Group B). Four sheep in each group underwent a veno-venous bypass for 72 hours. Every 6 hours, at 3 different blood flow rates (BFr) (400, 800, 1200 ml/min), at a constant gas flow rate (Gfr = 4 L/min), and at a constant blood inlet PCO₂ (45-55 mmHg), we measured the oxygenation performance (O₂ transfer = VO₂ and blood outlet PO₂ = PO₂out), CO₂ removal (CO₂ transfer = VCO₂ and PCO₂ outlet = PCO_2out) and pressure drop across the device (ΔP). A total of about 50 measurement sets were obtained for each group at different time points and blood flow rates. Both groups showed a good oxygenation performance (PO_2out always higher than 200 mmHg) and no differences were observed between the two groups (at 1200 ml/min BFr, the average VO₂ of all time points was 47 ± 15 ml/min in group A and 44 ± 11 ml/min in group B, mean ± SD, NS). During the first 24 hours, the VCO₂ was higher in Group B than in Group A at each BFr (at 1200 ml/min BFr, 81 ± 18 vs 67 ± 20 ml/min, p<0.01), while no differences were observed during the subsequent 48 hours. Throughout the entire experiment, VCO₂ increased with increasing BFr in both groups, (in group B, from 43 ± 14 ml/min at 400 ml/min BFr, to 73 ± 17 ml/min at 1200 ml/min BFr, average of all time points, p<0.01). In both groups the ΔP increased with the increasing BFr, but it was lower in Group B than in Group A at BFr 800 and 1200 ml/min (at 1200 ml/min BFr, 51 ± 15 mmHg vs 65 ± 17 mmHg, p<0.01), and remained stable for the entire experimental period.