A MATHEMATICAL-MODEL OF GAS-EXCHANGE IN AN INTRAVENOUS MEMBRANE-OXYGENATOR

Acute respiratory distress syndrome (ARDS) is a pulmonary edemic condi tion which reduces respiratory exchange in 150,000 people per year in the United States. The currently available therapies of mechanical ven tilation and extracorporeal membrane oxygenation are associated with h igh mortality rates, so intravenous oxygenation represents an attracti ve, alternative support modality. We are developing an intravenous mem brane oxygenator (IMO) device intended to provide 50% of basal oxygen and carbon dioxide exchange requirements for ARDS patients. A unique a spect of the IMO is its use of an integral balloon to provide active m ixing. This paper describes a mathematical model which was developed t o quantify and optimize the gas exchange performance of the IMO. The m odel focuses on balloon activated mixing, uses a lumped compartment ap proach, and approximates the blood-side mass transfer coefficients wit h cross-flow correlations. IMO gas exchange was simulated in water and blood, for a variety of device geometries and balloon pulsation rates . The modeling predicts the following: (1) gas exchange efficiency is reduced by a buildup of oxygen in the fluid near the fibers; (2) the I MO gas exchange rate in blood is normally about twice that in water un der comparable conditions; (3) a balloon diameter of about 1.5 cm lead s to optimal gas exchange performance; and (4) in viro positioning can affect gas exchange rates. The numerically predicted gas transfer rat es correlate closely with those experimentally measured in vitro for c urrent IMO prototypes. (C) 1998 Biomedical Engineering Society. [S0090 -6964(98)00602-X].