Is condensation the cause of plasma leakage in microporous hollow ®ber membrane oxygenators

Extracorporeal membrane oxygenators are comprised of large bundles of microporous hollow ®ber membranes (HFMs) across which oxygen and carbon dioxide are transferred to and from blood. Long term use of extracorporeal oxygenators is limited by plasma leakage through the pores of the HFM walls, requiring replacement of the oxygenator. Condensation of water vapor on the pore walls is thought to be a possible precursor to plasma leakage. To explore this mechanism, a simple theoretical analysis is used to examine the temperature of the gas ̄ow through the HFMs. For conditions representative of two commercially available oxygenators, the analysis predicts that the gas heats up to the temperature of blood ̄ow outside of the ®bers after passing through less than 0.5% of the ®ber lengths. Once the gas temperature and hence the ®ber wall temperature equilibrates with the blood, condensation of water vapor is no longer possible. In vitro testing of microporous HFMs under gas ̄ow rates and temperature conditions similar to those of extracorporeal oxygenators but with the ®bers submerged in water is also presented. The ®bers showed negligible degradation in carbon dioxide transfer over a four-day period. These results of both the theoretical and experimental analyses indicate that the condensation of water vapor within the pores of the HFMs is unlikely to be the cause of plasma leakage in clinically used extracorporeal oxygenators. # 1998 Published by Elsevier Science B.V. All rights reserved.