Spontaneous blood volume expansion (BVE) rate after mild (15%) and moderate (30%) pressure driven hemorrhage (PDH) in awake sheep

Introduction: After acute hemorrhage, blood volume expansion (BVE) depends on both fluid replacement and spontaneous transcapillary refill. We used pressure-driven hemorrhage (PDH) to determine the influence of the magnitude of hemorrhage on the rate of transcapillary refill in awake animals. Methods: Anesthetized adult ewes (n=6; 39±4 kg) were splenectomized, chronically instrumented and permitted a 5-d recovery period. Conscious sheep were randomly ordered to two PDH protocols: 1) 15% blood volume (BV) removal in 2-3 min or 2) 30% BV removal in 4-6 min. Protocols were separated by at least 72 h; no resuscitation was provided until 180 min after hemorrhage, at which time shed blood was reinfused. All animals tolerated the procedure. The time course of BVE was analyzed from changes in hemoglobin after measuring baseline plasma volumes using indocyanine green dye. Data are represented as means ± SEM. Results: After PDH, BV re-expanded to preshed values within 180 min in both groups. The difference in BVE rate is proportional to the bled volume of the two groups, with the 30% group's BVE rate double that of the 15% group throughout the 180-min observational interval. Both groups restored one-third of their BV deficit within 10 min and two-thirds of their BV deficit within 30 min after PDH. (See Figures) Conclusion: Spontaneous BVE rate is both rapid and proportional to bled volume and fully restores BV after both mild and moderate PDH.