Reduced cerebral blood flow, oxygen delivery, and electroencephalographic activity after traumatic brain injury and mild hemorrhage in cats

The authors investigated the effects of transient, mild hemorrhagic hypotension after fluid-percussion traumatic brain injury on intracranial pressure, cerebral blood flow (CBF), cerebral oxygen delivery (CBF x arterial O2 content), and electroencephalographic (EEG) activity. Adult mongrel cats were anesthetized with 1.6% isoflurane in N2O:O2 (70:30) and prepared for trauma and for radioactive microsphere CBF measurement. Isoflurane concentration was decreased to 0.8%, and the cats were randomly assigned to one of four control groups or to an experimental group. Animals in the four control groups underwent either mild hemorrhage (18 ml.kg-1) immediately followed by resuscitation with equal volumes of 10% Hetastarch (eight cats), mild hemorrhage followed by replacement of shed blood (six cats), isovolemic hemodilution with 18 ml.kg-1 of Hetastarch (six cats), or moderate (2.2 atm) trauma alone (eight cats). The experimental group received a combination of trauma and mild hemorrhage followed by resuscitation with Hetastarch (eight cats). Mild hemorrhage produced no significant changes in CBF, renal blood flow, or cardiac output. Following resuscitation from mild hemorrhage, mean arterial blood pressure, cardiac output, renal blood flow, and CBF were not significantly different from baseline; cardiac output and renal blood flow did not differ significantly from baseline 2 hours after Hetastarch resuscitation. Neither hemorrhage nor trauma alone produced significant decreases in CBF or in EEG activity, but trauma followed by hemorrhage and resuscitation produced significant (p less than 0.01) decreases in CBF, cerebral oxygen delivery, and EEG score. These data demonstrate that, following traumatic brain injury, even mild hemorrhagic hypotension is associated with significant deficits in cerebral oxygen availability and neurological function.