INTRAVASCULAR GAS TRANSFER - MEMBRANE-SURFACE AREA AND SWEEPING GAS-FLOWS ARE OF PRIME IMPORTANCE

Single and double hollow fiber intravascular gas exchangers were evalu ated in an extracorporeal veno-venous bypass circuit (right atrium to pulmonary artery) including a tubular blood chamber (mimicking caval v eins with an inner diameter of 26 mm) for evaluation of the membrane s urface area/host vessel diameter gas transfer relationships. Six bovin e experiments (body wt: 68 +/- 4 kg) with staged ex vivo blood flows o f 1, 2, 3, and 4 L/min and a device oxygen inflow of 0, 3, and 6 L/min (0 or 3 L/min/device) were performed. Total oxygen transfer at a bloo d flow of 1 L/min was 33 +/- 4 ml/min for a gas flow of 3 L/min (one d evice) vs 60 +/- 25 ml/min for a gas flow of 6 L/min (two devices); at a blood flow of 2 L/min, the corresponding oxygen transfer was 46 +/- 16 ml/min for a gas now of 3 L/min vs 95 +/- 44 ml/min for a gas flow of 6 L/min; at a blood flow of 3 L/min, the corresponding oxygen tran sfer was 48 +/- 24 ml/min for a gas flow of 3 L/min vs 92 +/- 37 ml/mi n for a gas flow of 6 L/min (p < 0.01 for comparison of areas under th e curves). Total carbon dioxide transfer at a blood flow of 1 L/min wa s 47 +/- 18 ml/min for a gas flow of 3 L/min vs 104 +/- 26 ml/min for a gas flow of 6 L/min; at a blood flow of 2 L/min, the corresponding c arbon dioxide transfer was 59 +/- 19 ml/min for a gas flow of 3 L/min vs 129 +/- 39 ml/min for a gas flow of 6 L/min; at a blood flow of 3 L /min, the corresponding carbon dioxide transfer was 60 +/- 22 ml/min f or a gas flow of 3 L/min vs 116 +/- 49 ml/min for a gas flow of 6 L/mi n (p < 0.01). For the given setup, the blood flow/gas transfer relatio nship is non linear, and a plateau is achieved at a blood flow of 2.5 L/min for O-2 and CO2. Doubling membrane surface area and consecutivel y sweeping gas flows result in doubling of gas transfers at all tested blood flows. However, increased membrane surface area and blood flow produce a higher pressure drop that in turn limits the fiber density t hat can be used clinically.