A METHOD FOR PREFERENTIAL DELIVERY OF VOLATILE ANESTHETICS TO THE IN-SITU GOAT BRAIN

Background: As part of studies aimed at better defining the effects of anesthetics at different anatomic sites, we have developed a model of preferentially delivering inhaled anesthetics to the in situ goat bra in, using a bubble oxygenator and roller pump. We tested the hypothese s that (1) this model excludes the cerebral circulation from the body; (2) the concentration of halothane in the oxygenator exhaust correlat es with the concentration of halothane in the oxygenator arterial bloo d. Methods: After ligation of the occipital arteries in six halothane- anesthetized goats, we used a bubble oxygenator to perfuse the brain p referentially (exclusive of the body) via a carotid artery, draining c ranial venous blood back into the oxygenator via the isolated jugular veins. (In goats, the vertebral arteries do not directly contribute to the cerebral circulation, and internal jugular veins and extracranial internal carotid arteries are absent.) The extent of isolation was de termined with radioactive microspheres injected into the left atrium during the following periods: (1) baseline; (2) during bypass when the blood pressure in the head equalled that in the body; (3) during bypa ss when the blood pressure in the body exceeded that in the head by ap proximately 30-35 mmHg; (4) when the bypass roller pump was stopped. W e also measured the concentration of halothane in the arterial blood o f the bypass unit. In three animals, systemic metocurine was administe red during bypass to detect the presence of venous contamination. Resu lts: Baseline cerebral blood now was 74+/-32 ml.100 g(-1).min(-1) (mea n +/- SD). During bypass, cerebral blood flow originating from the sys temic circulation was less than 1 ml.100 g(-1).min-l, and isolation ex tended to the caudal medulla during periods 3 and 4, and to the first l-cm segment of the spinal cord during period 2. The concentration of halothane in the oxygenator exhaust correlated reasonably well with th e arterial halothane concentration (r=0.82, P<0.001). Systemic arteria l metocurine concentrations peaked at 1 min (27+/-3.7 mu g/ml) and dec reased to 10.6+/-2.3 mu g/ml at 10 min; head venous metocurine plasma concentrations gradually increased to 3.1+/-0.4 mu g/ml at 10 min. Con clusions: This technique permits selective perfusion and delivery of i nhaled anesthetics to the ill situ goat brain, but is not adequate for selective delivery of fixed intravenous anesthetics.