INTRAVASCULAR OXYGENATION - INFLUENCE OF THE HOST VESSEL DIAMETER ON OXYGEN-TRANSFER

An extra corporeal venovenous bypass circuit (right atrium to pulmonar y artery), including an intravascular gas exchanger in a blood chamber with a Variable inner diameter; was developed far ex vivo evaluation of the host vessel diameter/intravascular oxygen transfer relationship . Three host vessel diameters mimicking different configurations of th e caval axis were:,studied in three bovine experiments (body weight 82 +/- 3 kg). Blood flow was 3,000 ml/min and device oxygen inflow was 2 ,300 ml/min. Serial blood samples were taken for 26 mm, 23 mm, and 20 mm inner blood chamber diameters after hemodynamic stabilization befor e and after exposure of the circulating blood to the intravascular gas exchanger (sampling ports at blood chamber inlet and outlet), Measure d oxygen saturation at the blood chamber inlet was 25.0 +/- 11.7% for the 26 mm diameter as compared to 31.7 +/- 12.6% for 23 mm, and 28.7 /- 9.2% for 20 mm. At the outlet, the corresponding O-2 saturations we re 34.5 +/- 11.5% for 26 mm, 42.9 +/- 8.8% for 23 mm, and 43.2 +/- 6.2 for 20 mm. Total O-2 transfer was 24.9 +/- 11.5 ml/min for 26 mm, 31. 9 +/- 7.4 ml/min for 23 mm, and 35.9 +/- 12.2 ml/min for 20 mm (p < 0. 05). Likewise, O-2 transfer rate was 8.3 +/- 3.8 ml/L, 10.6 +/- 2.4 ml /L, and 12.0 +/- 4.0 ml/L (p < 0.05). parallel analysts of fetal CO2 t ransfer and CO2 transfer rates provided less consistent findings. At 3 L/min, the pressure drop between the inlet and outlet of the blood ch amber was 12 +/- 3 mmHg for 26 mm, 26 +/- 1 mmHg for 23 mm, and 38 +/- 2 mmHg for 20 mm diameters (p < 0.001). The authors conclude that oxy gen transfer of a given intravascular gas exchanger appears to be indi rectly proportional to the host vessel diameter. Increasing blood pres sure gradient as a function of decreasing diameter has to be considere d in clinical application.