Blood volume redistribution during aortic cross-clamping. The scheme depicts the reason for the decrease in venous capacity, which results in blood volume redistribution from the vasculature distal to aortic occlusion to the vasculature proximal to aortic occlusion. If the aorta is occluded above the splanchnic system, the blood volume travels to the heart, increasing preload and blood volume in all organs and tissues proximal to the clamp. However, if the aorta is occluded below the splanchnic system, blood volume may shift into the splanchnic system or into the vasculature proximal to the clamp. The distribution of this blood volume between splanchnic and nonsplanchnic vasculature determines changes in preload. AoX = aortic cross-clamping; ↑ and ↓ = increase and decrease, respectively. Figure and legend reprinted from Gelman S: The pathophysiology of aortic cross-clamping and unclamping. Anesthesiology 1995; 82:1026–60 (fig. 1, p 1029).