Cardiovascular Effects of Centrally Administered Ketamine in Goats

Abstract

The cardiovascular effects of centrally and peripherally administered ketamine were evaluated in unanesthetized goats and in goats anesthetized with pentobarbital. Small doses of ketamine (0.1 to 4 mg.) were injected directly into the central nervous system (CNS) of the unanesthetized goats via a temporal artery catheter, while cerebral blood flow (CBF), cardiac output (C.O.), systemic blood pressure (B.P.), and heart rate (H.R.) were continuously monitored. Administered by this route, ketamine produced an immediate increase in mean systemic B.P., C.O., and H.R. Changes in CBF were variable, increasing on some occasions and decreasing on others. Cardiovascular changes were not the result of alterations in blood gases, since these remained unchanged. When ketamine, 0.1 to 4 mg., was injected into the temporal artery of goats anesthetized with pentobarbital, no changes were observed in B.P., C.O., H.R. or CBF. Ketamine (2 mg./kg.) intravenously administered to unanesthetized goats produced anesthesia and an increase in B.P., C.O., H.R., CBF, and arterial carbon dioxide (Paco2) levels. Administered by the same route and dosage in mechanically ventilated goats previously anesthetized with sodium pentobarbital, ketamine did not produce any changes in cardiovascular or blood-gas measurements. It was therefore concluded that ketamine produces peripheral sympathomimetic effects primarily by direct stimulation of CNS structures, and that when these structures are depressed by pentobarbital, the peripheral effects of ketamine are ameliorated.