PLASMA-CONCENTRATIONS AND CARDIOVASCULAR INFLUENCE OF LIDOCAINE INFUSIONS DURING ISOFLURANE ANESTHESIA IN HEALTHY DOGS AND DOGS WITH SUBAORTIC STENOSIS
An. Demoraes et al., PLASMA-CONCENTRATIONS AND CARDIOVASCULAR INFLUENCE OF LIDOCAINE INFUSIONS DURING ISOFLURANE ANESTHESIA IN HEALTHY DOGS AND DOGS WITH SUBAORTIC STENOSIS, Veterinary surgery, 27(5), 1998, pp. 486-497
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.