BARBITURATES AND HYPERVENTILATION DURING INTRACRANIAL HYPERTENSION

Objective. The purpose of this study was to determine the effect of hy perventilation alone and hyperventilation plus barbiturate therapy on intracranial pressure, global and regional cerebral blood flow rates, cerebrovascular resistance, and cerebral perfusion pressure in adult d ogs with and without intracranial hypertension induced by epidural bal loon. Design: Prospective, randomized, controlled study. Setting. An a nimal laboratory of a university hospital. Four sequential global and regional cerebral blood flow determinations were made in each animal d uring monitoring of heart rate and systemic arterial pressure, during respiratory control and arterial blood gas monitoring, intracranial pr essure monitoring, and with or without inflation of an epidural balloo n catheter. Subjects: Acute mongrel dogs obtained from the Baylor Cent er for Comparative Medicine. Five groups of animals were studied. In g roup 1, the response to hyperventilation was assessed in dogs without increased intracranial pressure. In group 2, the response to hypervent ilation was assessed in animals with acute intracranial hypertension. In group 3, the response to hyperventilation plus barbiturate therapy was assessed in dogs without increased intracranial pressure. In group 4, the response to hyperventilation plus barbiturate therapy was asse ssed in dogs with acute increased intracranial pressure. In group 5, a group of dogs with increased intracranial pressure was treated with n either hyperventilation nor barbiturates. Interventions: Hyperventilat ion, hyperventilation plus barbiturate therapy, or no interventions we re studied in these experimental paradigms. Measurements and Main Resu lts: The main outcome measures were changes in intracranial pressure a nd/or changes in regional or total cerebral blood flow. A significant decrease in intracranial pressure and cerebral blood flow rate was pro duced by hyperventilation alone in groups with intracranial hypertensi on. Combined hyperventilation and barbiturate therapy resulted in a si gnificant further decrease in cerebral blood flow rate in animals with normal and increased intracranial pressure, but no greater decrease i nintracranial pressure was seen compared with treatment with hypervent ilation alone. Cerebral perfusion pressures remained normal despite si gnificant decreases in cerebral blood flow rates. Conclusions: These s tudies suggest that barbiturate administration in this model of intrac ranial hypertension was no more effective in reducing increased intrac ranial pressure than hyperventilation alone.