Hypertonic saline does not improve cerebral oxygen delivery after head injury and mild hemorrhage in cats

Objectives: To investigate the effects of hypertonic saline for resuscitation after mild hemorrhagic hypotension combined with fluid percussion traumatic brain injury. Specifically, the effects of hypertonic saline on intracranial pressure, cerebral blood flow (radioactive microsphere method), cerebral oxygen delivery (cerebral oxygen delivery = cerebral blood flow x arterial oxygen content), and electroencephalographic activity were studied. Design: Randomized, controlled, intervention trial. Setting: University laboratory. Subjects: Thirty four mongrel cats of either sex, anesthetized with 1.0% to 1.5% isoflurane in nitrous oxide/oxygen (70:30). Interventions: Anesthetized (isoflurane) cats were prepared for traumatic brain injury, and then randomly assigned to the following groups: moderate traumatic brain injury only (2.7 +/- 0.2 atmospheres [atm], group 1); mild hemorrhage (18 mL/kg) only, followed immediately by resuscitation with 10% hydroxyethyl starch in 0.9% saline in a volume equal to shed blood (group 2); or both traumatic brain injury (2.7 +/- 0.1 atm) and mild hemorrhage, followed immediately by replacement of a volume equal to shed blood of 10% hydroxyethyl starch in 0.9% saline (group 3); or 3.0% saline (group 4). Measurements and Main Results: Data were collected at baseline, at the end of hemorrhage, and at 0, 60, and 120 mins after resuscitation (or at comparable time points in group 1). Intracranial pressure in group 1 was significantly increased by traumatic brain injury at the end of hemorrhage, immediately after resuscitation, and 60 mins after resuscitation (p < .02 vs. baseline). In group 2, intracranial pressure increased significantly only immediately after resuscitation (p < .0001 vs. baseline). Groups 3 and 4 exhibited higher, although statistically insignificant, intracranial pressure increases at 60 and 120 mins after resuscitation. During resuscitation, cerebral blood flow increased significantly (p < .02 vs, baseline) in the uninjured cats. In contrast, cerebral blood flow failed to increase during resuscitation in the cats subjected to traumatic brain injury before hemorrhage and resuscitation. Although cerebral oxygen delivery in group 2 decreased significantly immediately, 60 mins, and 120 mins after resuscitation (p < .001 vs. baseline) both groups 3 and 4 had significantly lower cerebral oxygen delivery at 60 and 120 mins after resuscitation (p < .01 and p < .005, respectively, vs. group 1 at 60 mins after resuscitation, and p < .01 and p < .01, respectively, vs. group 1 at 120 mins after resuscitation). Conclusions: After a combination of hemorrhage and traumatic brain injury, neither 10% hydroxyethyl starch nor 3.0% hypertonic saline restored cerebral oxygen delivery. Although neither trauma alone nor hemorrhage alone altered electroencephalographic activity, the combination produced significant decreases in electroencephalographic activity at 60 and 120 mins after resuscitation in groups 3 and 4, suggesting that cerebral oxygen delivery is inadequately restored by either resuscitation fluid. Therefore, traumatic brain injury abolished compensatory cerebral blood flow increases to hemodilution, and neither hydroxyethyl starch nor 3.0% hypertonic saline restored cerebral blood flow, cerebral oxygen delivery, or electroencephalographic activity after hemorrhagic hypotension after traumatic brain injury.