End-tidal carbon dioxide as an indicator of partial REBOA and distal organ metabolism in normovolemia and hemorrhagic shock in anesthetized pigs

Background: Partial resuscitative endovascular balloon occlusion of the aorta (REBOA) is a concept of aortic occlusion to reduce ischemic organ injuries below the occlusion level. It is, however, difficult to determine when the occlusion is partial in clinical settings. End-tidal carbon dioxide (ETCO2) is an aerobic metabolite and its production is reduced during ischemia. The aim of this study was to investigate if ETCO2 can be used as an estimate of the degree of aortic occlusion and distal organ metabolism during normovolemia and hemorrhagic shock in a porcine model. Methods: Nine pigs (25-32 kg) were anesthetized and surgically prepared. Zone 1 aortic occlusion by 33%, 66% and 100% of aortic blood flow was induced during normovolemia and controlled hemorrhagic grade IV shock. Hemodynamic and respiratory variables including ETCO2, aortic and mesenteric blood flow, femoral arterial blood pressure and blood gases were measured. Oxygen consumption and carbon dioxide production were correlated to measures of partial occlusion used in previous studies. Results: Aortic occlusion gradually lowered distal blood flow and pressure, whereas ETCO2, oxygen consumption and carbon dioxide production decreased at 66 % and 100 % of aortic occlusion. End-tidal carbon dioxide, and blood flow of the superior mesenteric artery and abdominal aorta, strongly correlated to oxygen consumption and carbon dioxide production, whereas femoral blood pressure did not. Conclusion: End-tidal carbon dioxide may be used as an estimator of partial REBOA and distal organ metabolism in both normovolemia and hemorrhagic shock.