The Direct Effects of Propofol on Pial Microvessels in Rabbits

Propofol is widely used for neurosurgical anesthesia; however, its effects on the pial microvasculature are unknown. We therefore evaluated the direct effects of propofol on pial microvessels in rabbits. Pial microcirculation was visualized using a closed cranial window technique in 20 Japanese white rabbits. In the first experiment (n=14), after baseline hemodynamic measurements, the cranial window was superfused with 5 increasing concentrations of propofol (10−8, 10−7, 10−6, 10−5, 10−4 mol/L; n=8) or intralipid (at comparable concentrations; n=6) dissolved in artificial cerebrospinal fluid for 7 minutes each. A typical anesthetic concentration of 5 μg/mL corresponds to 10−6 mol/L. In the second experiment (n=6), phenylephrine 10−6 mol/L and nitroglycerin 10−6 mol/L were applied topically for 7 minutes under pentobarbital anesthesia. In the third experiment (n=3), electroencephalogram and bispectral index were measured under pentobarbital anesthesia. Diameters of selected pial arterioles and venules were visualized with a microscope-video capture unit combination and subsequently measured with a digital video analyzer. Topical application of propofol at 10−8, 10−7, 10−6, or 10−5 mol/L did not alter the diameters of the pial microvessels; however, at 10−4 mol/L propofol induced dilation in large and small arterioles, along with venular dilation. Intralipid alone did not have any significant effect on vessel diameters. Phenylephrine and nitroglycerin produced pial arteriolar and venular constriction and dilation, respectively. Phenylephrine constricted and nitroglycerin dilated pial arterioles and venules. Pentobarbital did not produce either burst suppression or an isoelectric electroencephalogram. The results confirm our hypothesis: clinically relevant concentrations of propofol, that is, approximately 10−6 mol/L, do not dilate pial arterioles or venules.