EFFECTS OF INTRAVENOUS MEPIVACAINE ON RENAL SYMPATHETIC-NERVE ACTIVITY IN THE CAT DURING NITROUS-OXIDE AND NITROUS-OXIDE HALOTHANE ANESTHESIA

Background and Objectives. Because hemodynamic responses to systemic m epivacaine may be influenced by sympathetic change and concurrent gene ral anesthesia, the authors directly measured renal sympathetic nerve activity (RSNA) during intravenous administration of mepivacaine in su bseizure through seizure doses under N2O-O-2 and N2O-O-2-halothane ane sthesia. Methods. Thirty-four cats were randomly assigned to five grou ps. Groups I-A, I-B, and I-C received incremental subseizure doses of intravenous mepivacaine (2 mg/kg, 5 mg/kg, and 10 mg/kg). Groups II-A and II-B received intravenous infusion of mepivacaine (4 mg/kg/min). A nesthesia was maintained with N2O(70%)-O-2 ill groups I-A, I-C, and II -A, and with N2O (70%)-O-2-halothane (1%) in groups I-B and II-B. Cats in group I-C had undergone total baroreceptor denervation. Heart rate (HR), mean arterial pressure (MAP), and RSNA were measured. Results. In group I-A, MAP did not significantly change with intravenous mepiva caine, though RSNA and HR significantly decreased (P <.05) respectivel y with 5 mg/kg i.v. and 10 mg/kg i.v. mepivacaine. In group I-C, HR, M AP, and RSNA did not change significantly In group I-B, HR and MAP dec reased with bolus intravenous doses of mepivacaine in a dose-dependent fashion, but RSNA did not change significantly. All cats in group II- A developed seizure by mepivacaine infusion at mean total dose of 28.9 +/- 4.2 mg/kg without significant changes in HR, MAP, or RSNA. In gro up II-B, mepivacaine infusion resulted in circulatory collapse at mean total dose of 34.3 +/- 4.6 mg/kg without seizure or significant RSNA change. Conclusions. The authors conclude that intravenous mepivacaine induces occasional depression in HR and RSNA during N2O-O-2 anesthesi a, but in addition induces dose-related circulatory depression during N2O-O-2-halothane anesthesia via nonsympathetic mechanism(s).