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.