Objective: To compare early and delayed blood administrations in animals subjected to near-fatal hemorrhage in the presence of a vascular injury and resuscitated to different mean arterial pressures (MAPs).
Methods: Fifty-four immature swine with 4-mm infrarenal aortic tears were bled to a pulse pressure of 5 torr and then resuscitated (estimated blood loss 40 to 45 mL/kg). Groups I, II, and III were resuscitated with shed blood at a rate of 2 mL/kg/min, followed by normal saline at a rate of 6 mL/kg/min. Groups IV, V, and VI received the same fluids in reverse order. The fluids were infused intermittently to maintain MAPs of 40, 60, and 80 torr. The animals were observed for 60 minutes or until death.
Results: The animals resuscitated to a MAP of 80 torr experienced significantly higher intraperitoneal hemorrhage volumes and mortality than did the animals intentionally maintained hypotensive, regardless of whether blood or normal saline was administered first. There was no significant difference in mortality or hemorrhage volumes between any of the groups intentionally maintained hypotensive. The animals maintained at a MAP of 60 torr were significantly less acidotic than were the animals resuscitated with the same fluid regimen but to a MAP of 40 torr. Early blood administration also minimized the acidosis associated with hypotensive resuscitation.
Conclusion: In this model of near-fatal hemorrhage with a vascular injury, maintenance of the hypotensive state produced comparable improvements in one-hour survival and reductions in hemorrhage volume regardless of whether blood or saline was administered first. Although hypotensive resuscitation resulted in improved outcome, it was associated with significant acidosis. This effect was minimized with moderate rather than severe underresuscitation and early blood administration.