Abstract 10: Oxygen Transport Characterization of a Human Model of Hemorrhage
Introduction: Hemorrhage continues to be a leading cause of death from trauma sustained both in combat and in the civilian setting. The PULSE initiative identified the need to develop new models of resuscitation as well as new biosensors capable of detecting critical limitations of blood flow. To meet this need, new models of hemorrhage using humans may provide a better understanding of the early physiologic responses to hemorrhage as well as to serve as a platform to develop new monitoring and therapeutic techniques. We examined the oxygen transport changes produced by central volume redistribution in humans using lower body negative pressure (LBNP) as a hemorrhage mimetic.
Methods: Changes in oxygen delivery, oxygen consumption and tissue oxygenation and perfusion parameters measured in the skin, skeletal muscle, brain, and oral mucosa over increasing levels of LBNP were recorded in 20 volunteers. The LBNP protocol consisted of a 5-minute rest period (0 mm Hg) followed by 5 minutes of chamber decompression of the lower body to −15, −30, −45, and −60 mm Hg and additional increments of −10 mm Hg every 5 minutes until the onset of cardiovascular collapse. Data were analyzed using a repeated-measures mixed model analysis of variance.
Results: Statistically significant changes (p < 0.05) in oxygen delivery and tissue oxygenation and perfusion parameters, including oxygen extraction ratios of the skin, muscle, and brain were measured at several LBNP levels compared to baseline, while no significant changes were noted in oxygen consumption or systemic lactate or base excess. Imaging of the oral mucosa microvasculature also demonstrated significant reductions in functional capillary density.
Conclusion: The combination of findings indicate that LBNP produces appropriate changes at multiple tissue levels consistent with compensation from hemorrhage but that a frank state of shock (delivery dependent oxygen consumption) is not produced. Thus LBNP may provide a conscious human model to identify early markers of hemorrhage which may signal the need for intervention prior to the onset of shock. In this regard, it may also serve as a platform from which to produce and test new monitoring and therapeutic techniques appropriate for use in the setting of hemorrhage.