A COMPARISON OF THE RESPONSE OF NEAR-FATAL ACUTE HEMORRHAGE MODELS WITH AND WITHOUT A VASCULAR INJURY TO RAPID VOLUME EXPANSION

Recent studies in which animals were bled from a vascular injury rather than an intravascular catheter demonstrate increased blood loss and mortality with rapid volume expansion. The purpose of this study was to better define the importance of incorporating a vascular injury in animal models of acute hemorrhage. We directly compared the response to resuscitation from hemorrhage of comparable severity in animals with and without a vascular injury. Thirty-four immature swine (14.6 to 23.2 kg) were instrumented and subjected to severe blood loss (40 to 46 mL/kg). Groups I and II were hemorrhaged from a femoral artery catheter only. Groups III and IV were initially bled in the same manner; however, when the mean arterial pressure (MAP) decreased to 30 mm Hg, a 4-mm tear was created in the infrarenal aorta, allowing free intraperltoneal hemorrhage. In all groups, the catheter hemorrhage was discontinued once the pulse pressure reached 5 mm Hg. Groups II and IV were resuscitated with normal saline (NS) infused at a rate of 6 mL/kg/min followed by shed blood at a rate of 2 mL/kg/min. The resuscitation fluids were infused as needed to maintain a MAP of 80 mm Hg. Groups I and III served as controls and were not resuscitated. All animals were observed for 60 minutes or until death. The data were compared using repeated measures analysis of variance with a post hoc Tukey Kramer and the Fisher's exact test. Mortality was 100%, 0%, 88%, and 78% for groups I, II, III, and IV, respectively (P < .05 for group II vs groups I, III, and IV). Catheter hemorrhage volumes were 41 ± 4, 42 ± 2, 40 ± 5, and 37 ± 4 mL/kg (P < .05 for group II vs group IV), whereas intraperitoneal hemorrhage volumes were 0 ± 0, 0 ± 0, 7 ± 3, and 46 ± 11 mL/kg for groups I, II, III, and IV, respectively (P < .05 for group IV vs all other groups). The outcome from acute hemorrhage resuscitation is profoundly affected by the presence of a vascular lesion. Aggressive volume replacement causes a marked increase in blood loss from the site of vascular injury. Hemorrhage models that do not incorporate a vascular injury ignore this important pathophysiological event and, consequently, may not accurately simulate the response to therapeutic interventions. © 1993.