Oxygen transport characterization of a human model of progressive hemorrhage

Background: Hemorrhage continues to be a leading cause of death from trauma sustained both in combat and in the civilian setting. New models of hemorrhage may add value in both improving our understanding of the physiologic responses to severe bleeding and as platforms to develop and test new monitoring and therapeutic techniques. We examined changes in oxygen transport produced by central volume redistribution in humans using lower body negative pressure (LBNP) as a potential mimetic of hemorrhage. Methods and results: In 20 healthy volunteers, systemic oxygen delivery and oxygen consumption, skeletal muscle oxygenation and oral mucosa perfusion were measured over increasing levels of LBNP to the point of hemodynamic decompensation. With sequential reductions in central blood volume, progressive reductions in oxygen delivery and tissue oxygenation and perfusion parameters were noted, while no changes were observed in systemic oxygen uptake or markers of anaerobic metabolism in the blood (e.g., lactate, base excess). While blood pressure decreased and heart rate increased during LBNP, these changes occurred later than the reductions in tissue oxygenation and perfusion. Conclusions: These findings indicate that LBNP induces changes in oxygen transport consistent with the compensatory phase of hemorrhage, but that a frank state of shock (delivery-dependent oxygen consumption) does not occur. LBNP may therefore serve as a model to better understand a variety of compensatory physiological changes that occur during the pre-shock phase of hemorrhage in conscious humans. As such, LBNP may be a useful platform from which to develop and test new monitoring capabilities for identifying the need for intervention during the early phases of hemorrhage to prevent a patient's progression to overt shock.