Effects of Graded Doses of Epinephrine and of Norepinephrine on Blood Pressure Before and After Total Spinal Anesthesia

¹ From the Department of Pharmacology, University of Mississippi Medical Center, Jackson, Mississippi

Experiments have been carried out on dogs anesthetized with pentobarbital sodium to determine the effects of loss of all reflexes at the spinal level upon the responses to graded doses of epinephrine and norepinephrine. Total loss of reflexes was achieved by intraspinal injection of 2% procaine hydrochloride. The results of this study showed that in both the epinephrine and norepinephrine series of animals the maximum to which the blood pressure would rise was significantly lower after total spinal anesthesia than before. The actual rise in blood pressure was significantly greater at the higher doses tested after total spinal anesthesia. At the lower doses tested the differences between responses before and after total spinal anesthesia were slight and not significant. In all cases where there was a pressor response the duration of the pressor response was longer after total spinal anesthesia. In both the epinephrine and norepinephrine series of animals the differences in duration of pressor response reached an approximately constant value at the higher dosage levels. The dose-response curves were derived for each animal and the parameters were compared. The parameter a which has been defined as the theoretical maximum pressor response was significantly greater in both the epinephrine and the norepinephrine animals after spinal anesthesia. This was the only parameter significantly affected by the total spinal anesthesia.