PLASMA-CONCENTRATIONS AND CARDIOVASCULAR INFLUENCE OF LIDOCAINE INFUSIONS DURING ISOFLURANE ANESTHESIA IN HEALTHY DOGS AND DOGS WITH SUBAORTIC STENOSIS

Objective-To determine the plasma concentrations and cardiovascular ch anges that occur in healthy dogs and dogs with aortic stenosis that ar e given an infusion of lidocaine during isoflurane anesthesia. Study D esign-Phase I, controlled randomized cross-over trial; Phase 2, before and after trial Animals-Phase 1, 6 healthy dogs (4 female, 2 male) we ighing 23.8 +/- 7.4 kg; Phase 2, 7 dogs (4 female, 3 male) with modera te to severe subaortic stenosis (confirmed by Doppler echocardiography ) weighing 31.1 +/- 14.5 kg. Methods-After mask induction, intubation, and institution of positive pressure ventilation, instrumentation was performed to measure hemodynamic variables. After baseline, measureme nt at an end-tidal isoflurane concentration of 1.9% (phase 1) or 1.85% (phase 2), a loading dose infusion of lidocaine at 400 mu g/kg/min wa s given. Phase I: Maintenance doses of Lidocaine were administered con secutively (40, 120, and 200 mu g/kg/min) after the loading dose (give n for 10, 10, and 5 minutes, respectively) in advance of each maintena nce concentrations. Measurements were taken at the end of each loading dose and at 25 and 35 minutes during each maintenance level. The same animals on a different day were given dextrose 5% and acted as the co ntrol. Phase 2: Dogs were studied on a single occasion during an infus ion of lidocaine at 120 mu g/kg/min min given after the loading dose ( IO minutes). Measurements occurred after the loading dose and at 25 an d 35 minutes. A blood sample for lidocaine concentration was taken at 70 minutes. Data were compared using a one-way ANOVA for phase 1, and between phase 1 and 2. Statistical analysis for phase 2 was performed using a paired t-test with a Bonferroni correction. A P value less tha n or equal to .05 was considered significant. Results-Phase I: Plasma lidocaine concentrations achieved with 40, 120. and 200 mu g of lidoca ine/kg/min were 2.70, 5.27, and 7.17 mu g/mL, respectively. A signific ant increase in heart rate (HR) (all concentrations), central venous p ressure (CVP), mean pulmonary areterial pressure (PAP), and a decrease in stroke index (SI) (200 mu g/kg/min) were observed. An increase in systemic vascular resistance (SVR) and mean PAP, and a decrease in SI also followed the loading dose given before the 200 mu g/kg/min infusi on. No other significant differences from the control measurements, du ring dextrose 5% infusion alone, were detected. Phase 2: Plasma lidoca ine concentrations achieved were 5.35, 4.23, 4.23, and 5.60 mu g/mL at 10, 25, 35, and 70 minutes, respectively. They were not significantly different from concentrations found in our healthy dogs at the same i nfusions. A significant but small increase in CVP compared with baseli ne was noted after the loading dose. There were no significant differe nces from baseline shown in all other cardiovascular data. There were no statistically significant differences in any measurements taken dur ing the lidocaine infusion between the dogs in phase 1 and phase 2. Do gs with aortic stenosis tended to have a lower cardiac index than heal thy dogs at baseline (88 v 121 ml/kg/min) and during lidocaine infusio n (81 v 111 mL/kg/min). A small, statistically significant difference in systolic PAP was present at baseline. Conclusions-There does not ap pear to be any detrimental cardiovascular effects related to an infusi on of lidocaine at 120 mu g/kg/min during isoflurane anesthesia in hea lthy dogs or dogs with aortic stenosis. The technique used in this stu dy resulted in therapeutic plasma concentrations of lidocaine. Clinica l Relevance-Methods shown in the study can be used in clinical cases t o achieve therapeutic lidocaine levels without significant cardiovascu lar depression during isoflurane anesthesia. (C) Copyright 1998 by The American College of Veterinary Surgeons.