Brain injury causes loss of cardiovascular response to hemorrhagic shock

The combined cardiovascular effects of hemorrhagic shock and mechanical brain injury were modeled in five groups of pigs. Standard and hypertonic saline resuscitation of hypotension were evaluated. Changes in mean arterial pressure (MAP), heart rate (HR), central venous pressure (CVP), intracranial pressure (ICP), and brain water were measured. Brain injury (BI) was produced with a fluid percussion device that generated an extradural pressure of 3.5 x 10(5) N/m2 for 400 msec. Shock was caused by bleeding to a MAP of 60 mm Hg for 60 minutes and then resuscitated with shed blood only or shed blood plus 0.9% or 1.8% saline. Brain-injured only and shocked-only pigs served as controls. We found that brain injury alone caused refractory hypotension. Less shed blood was required to produce shock in brain injured animals (p < .05). Shock accompanied by brain injury was not reversed with crystalloid solutions. Volumes of saline required to restore blood pressure were large (> 6 L in 3 hours). 1.8% saline produced less rise in ICP than 0.9% saline but was less effective in restoring blood pressure. Brain edema was not decreased with 1.8% saline. Brain injury altered vascular compensation to hemorrhage and made accepted resuscitative measures ineffective.