Effect of intravenous lidocaine and ketamine on the minimum alveolar concentration of isoflurane in goats.
OBJECTIVE
To evaluate the effects of i.v. lidocaine (L) and ketamine (K), alone and in combination (LK), on the minimum alveolar concentration (MAC) of isoflurane (ISO) in goats.


METHODS
Randomized crossover design.


METHODS
Eight, adult mixed breed castrated male goats, aged 1-2 years weighing 24-51 kg.


METHODS
Anesthesia was induced with ISO that was delivered via a mask. The tracheas were intubated and the animals ventilated to maintain an end-tidal carbon dioxide partial pressure between 25 and 30 mmHg (3.3-4 kPa). Baseline MAC (MAC(B)) that prevented purposeful movement in response to clamping a claw was determined in triplicate. After MAC(B) determination, each goat received one of the following treatments, which were administered as a loading (LD) dose followed by a constant rate infusion, IV: L (2.5 mg kg(-1); 100 microg kg(-1) minute(-1)), K (1.5 mg kg(-1); 50 microg kg(-1) minute(-1)), L and K combination or saline, and the MAC (MAC(T)) was re-determined in triplicate. Plasma concentrations of L and K were measured around each MAC point and the values averaged.


RESULTS
The least-squares mean MAC(B) for all treatments was 1.13 +/- 0.03%. L, K, and LK reduced (p < 0.05) MAC(B) by 18.3%, 49.6% and 69.4%, respectively. Plasma concentrations for L, K, and LK were 1617 +/- 385, 1535 +/- 251 and 1865 +/- 317/1467 +/- 185 ng mL(-1), respectively. No change (p > 0.05) occurred with saline.


CONCLUSIONS
Lidocaine and K caused significant decreases in the MAC of ISO. The combination (LK) had an additive effect. However, the plasma L concentrations were less than predicted, as was the MAC reduction with L.


CONCLUSIONS
The use of L, K and the combination, at the doses studied, will allow a clinically important reduction in the concentration of ISO required to maintain general anesthesia in goats.
Doherty
Tom
T
Department of Large Animal Clinical Sciences, College of Veterinary Medicine, University of Tennessee, Knoxville, TN 37996, USA. tdoherty@utk.edu
Redua
Marcia A
MA
Queiroz-Castro
Patricia
P
Egger
Christine
C
Cox
Sherry K
SK
Rohrbach
Barton W
BW
D000768:Anesthesia, General / Q000662:veterinary*; D019162:Anesthetics, Combined / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology; D018685:Anesthetics, Inhalation / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics*; D000779:Anesthetics, Local / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*; D000818:Animals; D018592:Cross-Over Studies; D006041:Goats / Q000378:metabolism / Q000502:physiology*; D007262:Infusions, Intravenous / Q000662:veterinary; D007530:Isoflurane / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics*; D007649:Ketamine / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology; D008012:Lidocaine / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology; D008297:Male; D011650:Pulmonary Alveoli / Q000378:metabolism*
D019162:Anesthetics, Combined; D018685:Anesthetics, Inhalation; D000779:Anesthetics, Local; D007649:Ketamine; D008012:Lidocaine; D007530:Isoflurane