BLOOD-VOLUME RESTITUTION AND GROWTH IN FETAL LAMBS AFTER ACUTE HEMORRHAGE

The effects of 15-50% fetal hemorrhage (at similar to 1%/min) were stu died in 13 pregnant ewes at 130-135 days of gestation for up to 5 days posthemorrhage. The upper limit of acute blood loss appears to be sim ilar to 45%, and the rate of restoration of blood volume decreases wit h the severity of hemorrhage, particularly with hemorrhage > 30-40%. T he restoration of fetal blood volume was due primarily to the restorat ion of plasma volume; in the animals subject to 40-45% blood loss (n = 9), red cell mass was still only 69.1 +/- 3.9% of the prehemorrhage v alue at day 5 posthemorrhage. There appear to be two phases in the res toration of plasma: 1) plasma volume was restored by 2 h posthemorrhag e and 2) the restoration of plasma protein mass occurred primarily fro m 2 to 24 h. There was a significant correlation between blood volume and plasma protein mass. However, the regression line for the posthemo rrhage days was shifted significantly upward in relation to that for t he hemorrhage day because of a significant rise of plasma protein conc entration. This may be important for the maintenance of blood volume a fter hemorrhage. Finally, fetal growth rate was determined by comparin g fetal weight estimated in utero (from blood volume) with birth weigh t in 12 nonhemorrhaged control fetuses and in the 9 fetuses subject to 40-45% hemorrhage. The average rate of growth per day was 1.57 +/- 0. 34% and -1.82 +/- 1.02%, respectively. The latter value is not signifi cantly different from zero, suggesting that the acute blood loss impai red fetal growth.