VENOVENOUS ECMO ALLOWS COMPLETE GAS-EXCHANGE IN OVINE ARDS

In acute respiratory distress syndrome (ARDS), ECMO is the final appro ach to maintain adequate blood gases because of its ability to provide complete gas exchange. In newborns, veno-venous access proved to be s uperior to veno-arterial. Veno-venous ECMO for adults, however, is not established yet. Thus we designed such a system and tested it in shee p. Methods: In sheep (N = 7, mean weight 94 +/- 2 kg) a 28 F catheter was advanced through the right jugular vein into the caudal caval vein with a second aperture in the cranial caval vein. A second withdrawal catheter (20 F) was placed in cranial direction. Oxygenated blood was reinjected through a 20 F catheter, positioned through the left jugul ar vein into the right atrium. Postoperatively, the ECMO system was te sted in conscious, spontaneously breathing sheep with an extracorporea l oxygen and blood flow (EBF, EOF) of 61/min. ARDS was then induced by pressure controlled ventilation, and ECMO was started again. After in dividual adjustment of EBF and EOF, both were increased by 2 1/min eac h. At all time points, hemodynamic readings and blood gases were taken . Results: In healthy sheep, ECMO led to a significant decrease in res piratory minute volume from 12.4 +/- 0.2 to 1.4 +/- 0.4 1/min, while b lood gases remained unchanged. After development of ARDS any spontaneo us pulmonary gas exchange could be excluded. ECMO provided complete ga s exchange. A further increase in EOF significantly lowered PaCO2 (42. 9 +/- 6.9 vs. 34.3 +/- 5.2 mmHg), whereas an increase in EBF significa ntly improved PaO2 (88.9 +/- 15.7 vs. 106.1 +/- 18.5 mmHg). Changes in EBF never had any effect on systemic or pulmonary blood pressure. No significant recirculation occured. Discussion: The efficacy of this EC MO system is proven by the fact that conscious sheep had nearly no nee d to breathe, and adequate blood gases were maintained after lung inju ry was sustained. These effects were accompanied by extremely stable s ystemic and pulmonary hemodynamics.