[The effects of systemic bupivacaine on baroreflex sensitivity in dogs].

To evaluate the effects of systemic bupivacaine on the baroreflex control of heart rate, we investigated the baroreflex sensitivity assessed with a pressor and a depressor test using phenylephrine and nitroglycerin in pentobarbital anesthetized dogs (n = 12). Intravenous injection of bupivacaine (mean plasma concentration of 2.4 +/- 0.9 micrograms.ml-1) caused a significant suppression of the baroreflex sensitivity, defined by the slopes of regression line (in msec of RR interval change per mmHg increase or decrease in systolic blood pressure). The sensitivity obtained with the pressor and the depressor tests decreased from 6.0 +/- 2.3 to 3.5 +/- 1.7, from 2.4 +/- 1.3 to 1.3 +/- 0.8 msec.mmHg-1, respectively (P < 0.01). Suppression of the baroreflex sensitivity during epidural anesthesia with bupivacaine could be due not only to cardiac sympathectomy but also to a direct effect of bupivacaine on the reflex arch including the receptors, the afferent nerve pathways, the CNS, the efferent pathway, and the effector organs. Therefore, the hemodynamic responses to reduction of blood pressure are likely to be inhibited by epidural bupivacaine.