Small changes, big effects: The hemodynamics of partial and complete aortic occlusion to inform next generation resuscitation techniques and technologies

BACKGROUND: The transition from complete aortic occlusion during resuscitative endovascular balloon occlusion of the aorta can be associated with hemodynamic instability. Technique refinements and new technologies have been proposed to minimize this effect. In order to inform new techniques and technology, we examined the relationship between blood pressure and aortic flow during the restoration of systemic circulation following aortic occlusion at progressive levels of hemorrhage. METHODS: An automated supraceliac aortic clamp, capable of continuously variable degrees of occlusion, was applied in seven swine. The swine underwent stepwise removal of 40% of their total blood volume in four equal aliquots. After each aliquot, progressive luminal narrowing to the point of complete aortic occlusion was achieved over 5 minutes, sustained for 5 minutes, and then released over 5 minutes. Proximal and distal blood pressure and distal aortic flow were continuously recorded throughout the study. RESULTS: Upon release of the clamp, hyperemic aortic flow was observed following 10% and 20% hemorrhage (1,599 ± 785 mL/min, p < 0.01; and 1,070 ± 396 mL/min, p < 0.01, respectively). Proximal blood pressure exhibited a nonlinear relationship to aortic flow during clamp removal; however, distal blood pressure increased linearly with distal flow upon clamp opening across all hemorrhage volumes. CONCLUSIONS: Hyperemic blood flow following return of circulation may contribute to cardiovascular collapse. Reintroduction of systemic blood flow after aortic occlusion should be guided by distal blood pressure rather than proximal pressure. Awareness of hemodynamic physiology during aortic occlusion is of paramount importance to the clinical implementation of next-generation resuscitative endovascular balloon occlusion of the aorta techniques and technologies.