The effect of augmented hemodynamics on blood flow during arteriovenous carbon dioxide removal.

Arteriovenous carbon dioxide removal (AVCO2R) as an alternative treatment for acute respiratory distress syndrome uses a low resistance gas exchanger in a simple arteriovenous shunt to achieve total CO2 removal and allow lung rest. We have previously shown in our clinically relevant LD40 ovine model of smoke/burn induced acute respiratory distress syndrome that AVCO2R allows significant decreases in respiratory rate, tidal volume, peak airway pressure, and FiO2, as compared with standard mechanical ventilation. In addition, we have shown in a prospective randomized outcomes study that AVCO2R increases ventilator free days, decreases ventilator dependent days, and significantly improves survival. The purpose of this study is to further define the limits of AVCO2R through hemodynamic augmentation and evaluation of peak end expiratory pressure (PEEP). Administration of an alpha agonist (phenylephrine) and a beta agonist (isoproterenol) increased mean arterial pressure (MAP) and cardiac output (CO), respectively. MAP increases ranged from 2.4% to 94.4% and CO increases ranged from 33% to 146%. Phenylephrine caused elevations in MAP (2.4-94.4%) and AVCO2R flow (9-67%), and CO never decreased more than 10%. Isoproterenol administration increased CO (33-146%), decreased MAP (9-54%), and decreased AVCO2R flow (11-42%). In a second group, PEEP was increased stepwise from 0 (baseline) to 20 cm H2O. Increasing PEEP did not result in significant hemodynamic changes (< 10% change from baseline PEEP) for MAP, CO, or AVCO2R flow. In conclusion, alpha agonist administration increased AVCO2R blood flow, whereas beta agonist administration decreased MAP and AVCO2R blood flow, despite CO elevation. Various levels of PEEP are well tolerated and thus allow a range of options during AVCO2R.