Vascular retention of saline following acute and subacute hemorrhage in dogs.

Acute hemorrhage is usually associated with compensatory mechanisms calculated to replenish the vascular compartment. In the present study, we studied the transvascular distribution of an isotonic saline load (7% body weight) delivered to supine anaesthetized dogs following acute (20-25 ml/kg blood removed on the morning of the study) or subacute (20-25 ml/kg blood removed 16-18 h before the study) hemorrhage. In 10 dogs subjected to subacute hemorrhage, plasma volume was unaltered from control values 3 h post-load, and 6/10 animals also lost original plasma volume. Only 5.8% of the anticipated volume was retained within the vascular space. The percentage of extracellular fluid (ECF) partitioned as plasma declined from 33 to 23% (p less than 0.05). In 6 dogs with acute hemorrhage treated the same way, plasma volume increased by 24% at 3 h post-loading and 59.8% of the available volume now remained intravascularly. The percentage of ECF partitioned as plasma declined from 30 to 26%, a change of only 13% compared to a decline of 30% observed for the subacute group. We conclude that a delay in replenishing the ECF following hemorrhage may profoundly alter the volume of infused isotonic saline retained within the vascular compartment.