A comparison of the effects of norepinephrine, epinephrine, and dopamine on cerebral blood flow and oxygen utilisation.

The concomitant effects of infusions of catecholamines on cerebral blood flow (CBF), intracranial pressure (ICP), arterio-venous oxygen content difference (AVDO2), and cerebral oxygen utilization (COU) were prospectively studied in an intact cerebral autoregulatory model. Epinephrine, norepinephrine and dopamine were infused at doses used in clinical practice in awake, chronically catheterized sheep (n = 5). Mean arterial pressure (MAP), CBF and ICP were measured continuously, COU was expressed as delta CBF x AVDO2. All 3 drugs significantly increased MAP in a dose dependent manner. Norepinephrine and epinephrine had no significant effects on ICP, CBF, AVDO2 or COU at infusions of 0-60 micrograms/min. Infusions of dopamine from 0-60 micrograms/kg/min resulted in statistically significant increases in ICP (+34.5 +/- 3.7 to +97.2 +/- 6.8) and CBF (+13.3 +/- 3.2 to +52.6 +/- 24.3) (% change baseline +/- SEM, 95% CI, ANOVA), reduction in AVDO2 (3.54 +/- 0.2. to 2.69 +/- 0.2 mg%) and a biphasic response in COU. In the intact physiological model, induced hypertension by epinephrine and norepinephrine is not associated with global changes in CBF, ICP or COU which remain constant. At equivalent doses, dopamine causes cerebral hyperaemia, increased ICP and increased global cerebral oxygen utilization.