Abstract 281: Traumatic Brain Injury Accelerates Onset of Hypotension with Less Blood Lost in a Pressure-Guided Model of Polytrauma with Uncontrolled Hemorrhage by Aortic Tear

Abstract

Objective: Traumatic brain injury (TBI) is thought to exacerbate the severity of hemorrhagic shock by interfering with compensatory neurovascular reflexes. However, this effect remains undefined. We use a swine model of uncontrolled hemorrhage by aortic tear to examine the effect of TBI on blood pressure and blood loss during shock. We hypothesize that TBI accelerates onset of hypotension during hemorrhage with less blood lost. Methods: Anesthetized domestic swine were hemorrhaged at a controlled rate by arterial catheter to mean arterial pressure (MAP) of 30mmHg and maintained for 15 minutes. Aortic tear allowing free bleeding was made when MAP = 50 mmHg during initial catheter hemorrhage. TBI was achieved by a fluid percussion device applied directly to the Dura just prior to hemorrhage. Time intervals to goal MAP, catheter hemorrhage volumes, and metabolic parameters were recorded during the hemorrhage and shock periods. A control group without TBI was similarly instrumented and hemorrhaged for comparison. Variables were compared in animals with and without TBI using T-tests and associations were examined using correlation. Results: N= 30 swine weighing mean (SD) 27(3.4) kg were compared (21 with TBI vs. 9 without TBI). The TBI group achieved goal MAP=30mmHg after aortic tear significantly faster (TBI= 1.0 min vs. No TBI=1.9 min, p=0.016). The TBI group required significantly less additional blood withdrawn to maintain goal MAP during the 15 minute shock period (TBI= 5.8ml/kg vs. No TBI=11.6ml/kg, p=<0.0001). Yet, lactate accumulation was similar between groups (TBI= 4.7mmol/l vs. No TBI=4.4mmol/l, p=0.68). Mean percussive pressure at the Dura = 3.4(0.4) atm in the TBI group. Dural pressure was positively associated with rate of blood pressure change to MAP=50mmHG (R=0.41, p=0.026) and with total lactate concentration at the end of the shock period (R=0.55, p=0.002). Conclusion: In this model, animals with TBI demonstrated an altered blood pressure response to hemorrhage. Current guidelines for estimating blood loss using blood pressure may not apply in the setting of hemorrhagic shock with TBI.