Ex vivo testing of the intravenous membrane oxygenator

Intravenous oxygenation represents a potential respiratory support modality for patients with acute respiratory failure or with acute exacerbations of chronic respiratory conditions. Our group has been developing an intraveno us oxygenator, the IMO, which uses a constrained fiber bundle and a rapidly pulsating balloon within the fiber bundle. Balloon pulsation drives blood flow past the fibers at greater relative velocities than would otherwise ex ist within the host vessel, and gas exchange rates are enhanced. The purpos e of this study was twofold: (1) to characterize the gas exchange performan ce of the current IMO in an extracorporeal mock vena cava vessel under cond itions of known fixed vessel geometry and controlled blood flow rates; and (2) to compare the IMO gas exchange performance to that reported for the cl inically tested IVOX device within a comparable ex vivo set-up. The ex vivo flow loop consisted of a 1 inch ID tube as a mock vena cava that was perfu sed directly from an anesthetized calf at blood flow rates ranging from 1 t o 4 1/2 L/min. O-2 and CO2 exchange rates were measured for balloon pulsati on rates,which ranged from 0 to 180 bpm. Balloon pulsation significantly in creased gas exchange, by 200-300% at the lowest blood flow rate and 50-100% at the highest blood flow rate. Balloon pulsation eliminated much if not a ll of the dependence of the gas exchange rate on blood flow rate as seen in passive oxygenators. This suggests that in clinical application the IMO ma y exhibit less gas transfer variability due to differences in cardiac outpu t Over the entire flow rate range studied, the CO2 and O-2 gas exchange rat es of the IMO at maximal balloon pulsation varied from approximately 250 to 350 ml/min/m(2). At maximum balloon pulsation the IMO exchanged CO2 and O- 2 at rates from 50-500% greater, depending upon the blood flow rate, than t he exchange rates reported for the IVOX device in ex vivo tests.