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 intravenous 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 exist within the host vessel, and gas exchange rates are enhanced. The purpose of this study was twofold: (1) to characterize the gas exchange performance of the current IMO in an extracorporeal mock vena cava vessel under conditions of known fixed vessel geometry and controlled blood flow rates; and (2) to compare the IMO gas exchange performance to that reported for the clinically 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 perfused directly from an anesthetized calf at blood flow rates ranging from 1 to 4 1/2 L/min. O2 and CO2 exchange rates were measured for balloon pulsation rates, which ranged from 0 to 180 bpm. Balloon pulsation significantly increased 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 all 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 may exhibit less gas transfer variability due to differences in cardiac output Over the entire flow rate range studied, the CO2 and O2 gas exchange rates of the IMO at maximal balloon pulsation varied from approximately 250 to 350 ml/min/m2. At maximum balloon pulsation the IMO exchanged CO2 and O2 at rates from 50-500% greater, depending upon the blood flow rate, than the exchange rates reported for the IVOX device in ex vivo tests.

Acute in vivo testing of an intravascular respiratory support catheter.

Current treatment for acute respiratory failure (ARF) includes the use of mechanical ventilation and/or extracorporeal membrane oxygenation, both of which can exacerbate lung injury. Intravenous respiratory support, using hollow fiber membranes placed in the vena cava, represents an attractive potential treatment for ARF, which could help reduce or eliminate ventilator induced trauma and/or other problems. Our group has been developing a respiratory support catheter (the Hattler catheter [HC]) that consists of a constrained hollow fiber bundle with a centrally located balloon. The balloon can be pulsated rapidly to increase blood flow across the fibers and decrease diffusional transfer resistance there, thus increasing gas exchange. The purpose of this study was to evaluate the HC in acute animal implants and to compare performance with that achieved in previous ex vivo studies. The HC was implanted into four calves by means of the external jugular vein and placed in the superior and inferior vena cava spanning the right atrium. Gas exchange, hemodynamics, and hematologic parameters were assessed over a range of balloon pulsation rates from 30 to 300 beats/minute. A <10% reduction in cardiac output was associated with catheter insertion and operation. The maximum CO2 exchange rate occurred at the highest pulsation rate and averaged 56 +/- 3 ml/min, or 327 +/- 15 ml/min per m2 when averaged to catheter membrane area, a level comparable to that achieved in the previous ex vivo studies. Balloon pulsation did not produce significant levels of hemolysis, as plasma-free hemoglobin remained below 10-15 mg/dl.