Epinephrine, norepinephrine and dopamine infusions decrease propofol concentrations during continuous propofol infusion in an ovine model

Objective: To determine the effects of exogenous ramped infusions of epinep hrine, norepinephrine and dopamine on arterial and effluent brain blood con centrations of propofol under steady state intravenous anesthesia. Design: Prospective, randomized animal study. Setting: University research laboratory. Subjects: Five adult female merino sheep. Interventions: Induction (5 mg/kg) and continuous infusion of propofol (15 mg/min) with controlled mechanical ventilation to maintain PaCO2 40 mmHg. A fter 1 h of continuous anesthesia, each animal randomly received ramped inf usions of epinephrine, norepinephrine (10, 20, 40 mug/min) and dopamine (10 , 20, 40 mug.kg. min) in 3 x 5 min intervals followed by a 30-min washout p eriod. Measurements: Arterial and sagittal sinus whole blood for determination of propofol concentrations using high-pressure liquid chromatography. Cardiac output using a thermodilution method. Level of consciousness using an obser vational scale. Main results: All three drugs significantly and transiently increased cardi ac output in a dose-dependent fashion to a maximum of 146-169% of baseline. Baseline arterial and sagittal sinus propofol concentrations were not stat istically different prior to catecholamine infusions. All three drugs signi ficantly reduced mean arterial propofol concentrations (95% CI, p < 0.05): epinephrine to 41.8% of baseline (11.4-72), norepinephrine to 63% (27-99) a nd dopamine to 52.9% (18.5-87.3). There were parallel reductions of concent rations in sagittal sinus blood leaving the brain. The lowest blood concent rations were associated with emergence from anesthesia. Arterial concentrat ions were inversely related to the simultaneously determined cardiac output (r(2) = 0.74, P < 0.0001). Comparison of the data with the predictions of a previously developed recirculatory model of propofol disposition in sheep showed the data were consistent with a mechanism based on increased first pass dilution and clearance of propofol secondary to the increased cardiac output. Conclusions: Catecholamines produced circulatory changes that reversed prop ofol anesthesia. These observations have potential clinical implications fo r the use of propofol in hyperdynamic circulatory conditions, either induce d by exogenous catecholamine infusions or pathological states.