Blood volume restitution after hemorrhage in the newborn lamb

Blood volume restitution after hemorrhage was investigated in lambs in the first week of life. Two groups of nonsplenectomized lambs were bled 10 and 20% of their blood volume at 2%/min while being suspended horizontally in a sling with their legs dependent, and a third group was bled 20% while lying down. Blood pressure fell 8% in the lambs bled both 10 and 20% while lying down and 44% in those bled 20% while being suspended. Blood volume was completely restored in all three groups by 5 h after the hemorrhage, the rate of restitution being equal among the groups. The initial phase of restitution was slower when the lambs were bled while lying down. Vasopressin levels were increased only in the lambs bled 20% of their blood volume while being suspended. Plasma renin activity increased similarly in all groups. Hemorrhage increased plasma glucose but did not change plasma protein and serum osmolality. We conclude that lambs bled up to 20% of blood volume restitute relatively quickly at a rate independent of the volume shed. The position of the animal affects the degree of hypotension, the levels of vasopressin, and the rate of the initial phase of volume restoration.