Blood Recirculation Enhances Oxygenation Efficiency of Artificial Lungs

Ambulating patients on extracorporeal membrane oxygenation (ECMO) or extracorporeal CO2 removal (ECCO2R) improves outcomes. These systems would further simplify ambulation if made more compact. This study investigates blood recirculation to decrease device size by increasing efficiency. The required hollow fiber membrane (HFM) area was determined by numerically modeling gas transfer. An oxygenation device with recirculating blood flow was designed using computational fluid dynamics (CFD). Hydrodynamic performance and shear stresses of the device were analyzed using CFD at 2,000, 2,250 and 2,500 RPM. A prototype (0.38 m) was manufactured for in-vitro oxygenation testing. Oxygenation was measured at a constant 3.5 L/min blood flow while recirculation flow rate varied up to 6.5 L/min. Hemolysis was measured at 3.5 L/min blood flow and 6.5 L/min recirculation flow. A 0.3 m prototype device was used to test in-vitro ECCO2R recirculation at a constant 500 ml/min blood flow rate and recirculation flow rates up to 5.5 L/min. Computational fluid dynamics analysis showed that the oxygenation device could produce over 250 mm Hg while maintaining 3.5 L/min blood flow and 6.5 L/min recirculation flow. The model predicted oxygenation within 8% and overestimated ECCO2R by up to 32%. Measured gas transfer was 180 ml O2/min and 62 ml CO2/min. Normalized index of hemolysis contribution of the HFM was 0.012 gm/100 L.