Organ blood flow during arteriovenous carbon dioxide removal

Animal models of arteriovenous carbon dioxide removal (AVCO₂R) have achieved lung rest during treatment of severe respiratory failure, with total CO₂ removal at arteriovenous shunt flow rates of 10% to 25% of cardiac output (CO). Previously, no statistically significant changes were reported in heart rate, cardiac output, mean arterial pressure, or pulmonary arterial pressure during prolonged (7 days) AVCO₂R with shunt flows to 25% of CO. In this study, to determine the effect of various shunt levels on organ blood flow, colored microspheres were used in a conscious ovine model of AVCO₂R. A low resistance 2.5 m₂ oxygenator was placed in a simple carotid-to-jugular arteriovenous circuit. The AVCO₂R flow (Qb) was incrementally increased to 5%, 10%, 15%, 20%, and 25% of baseline CO. After equilibration, colored microspheres were injected into a left atrial catheter while reference blood was withdrawn from an arterial line at a constant rate. Organ blood flow obtained by measuring microspheres in the tissues, showed approximately a 10- 20% decrease at a 5% shunt, but remained relatively unchanged thereafter at up to a 25 % shunt, and was well tolerated without hemodynamic sequelae or evidence of end organ ischemia. It was concluded that AVCO₂R can achieve lung rest during respiratory failure at flow rates of 10-25% CO, with a resultant mild decrease in critical organ blood flow that appears well tolerated.