Evaluation of Two Microporous Polypropylene Membrane Lungs for Extracorporeal Carbon Dioxide Removal during Apneic Oxygenation

_____________ _ Five Capiox II 33 (Terumo Corporation) and nine M-2000 (Shiley Incorporated) microporous polypropylene membrane lungs were evaluated for dynamic operating characteristics during apneic oxygenation. Particular emphasis was placed on carbon dioxide and oxygen transfer (VC02 and V02 respectively). The lungs were incorporated into extracorporeal venavenous bypass circuits used with the pigs of 36.5 kg average weight. vco2 was determined by analyzing outlet gas composition and vo2 was determined with the Fick technique. Blood flow rate was held constant at 1 L!min in all trials. Peak VC02 o.ccurred at gas flow rates of 4 L!min and 6 L!min for the Capiox II 33 and M-2000 respectively. Both lungs eliminated C02 in quantities sufficient for complete ventilatory support during apneic oxygenation over the 5-8 hour experiments. V02 for the Capiox II 33 was 18.2 and 45.6 ml/ min with an inlet oxygen saturation of 70% and Fi02 of 0.209 and 1.0 respectively. Under the same conditions, the V02 for the M-2000 was 27.2 and 43.1 mll min. Both lungs operated with low gas inlet pressures over the gas flow rates used and the blood path pressure drop averaged 42.2 and 20.7 mmHg for the Capiox II 33 and M-2000 respectively. Introduction ______________ _ Gattinoni et al. 14 have reported clinical trials of a ventilatory support technique for patients in acute respiratory failure. Identified as low frequency positive pressure ventilation (LFPPV) with extracorporeal C02 removal (ECC02R), it is best characterized as a separation Supported in part by grants from the American Society of Extracorporeal Technology and NIH HL-29715 Direct communications to: Philip D. Beckley, M.S. Circulation Technology 1583 Perry Street Columbus, OH 43210 •• 76 of the gas exchange functions of the lungs. s-s Oxygenation of the patient occurs primarily via apneic oxygenation with periodic inflations of the lung at low frequencies (2 to 3 breaths per minute). Carbon dioxide elimination is achieved via a low-flow veno-venous extracorporeal bypass through a membrane lung. It is suggested that LFPPV with ECC02R minimizes many of the complications and risks associated with conventional positive pressure ventilation or high-flow venoarterial extracororeal membrane oxygenation. •• Artificial lungs constructed of silicone rubber membrane material have been used in the clinical trials. Kolobow introduced a silicone rubber spiral coiled membrane lung specifically constructed for removal of carbon dioxide. Microporous membrane lungs, however, offer promise in this technique due to their low resistance to carbon dioxide transfer and are perhaps ideally suited for ECC02R. . 12 In addition to efficient C02 removal, the membrane lung chosen for this application should also have the capability of transferring oxygen in amounts sufficient to augment the apneic oxygenation process, have minimal blood and gas path resistance, be easily manageable as an extracorporeal device, and be able to perform over long periods of ventilatory support. This study describes the evaluation of two microporous polypropylene membrane lungs used for ECC02R in a pig model of acute respiratory failure. The lungs were specifically evaluated with respect to their efficiency of carbon dioxide elimination, augmentation of oxygen transfer, and physical dynamic