Objective—To determine induction characteristics and the minimum alveolar concentration (MAC) at which consciousness returned (MACawake) in dogs anesthetized with isoflurane or sevoflurane.
Animals—20 sexually intact male Beagles.
Procedures—In experiment 1, 20 dogs were randomly assigned to have anesthesia induced and maintained with isoflurane or sevoflurane. The MAC at which each dog awoke in response to auditory stimulation (MACawake-noise) was determined by decreasing the end-tidal concentration by 0.1 volume (vol %) every 15 minutes and delivering a standard audible stimulus at each concentration until the dog awoke. In experiment 2, 12 dogs received the same anesthetic agent they were administered in experiment 1. After duplicate MAC determination, the end-tidal concentration was continually decreased by 10% every 15 minutes until the dog awoke from anesthesia (MACawake).
Results—Mean induction time was significantly greater for isoflurane-anesthetized dogs (212 seconds), compared with the sevoflurane-anesthetized dogs (154 seconds). Mean ± SD MACawake-noise was 1.1 ± 0.1 vol % for isoflurane and 2.0 ± 0.2 vol % for sevoflurane. Mean MAC was 1.3 ± 0.2 vol % for isoflurane and 2.1 ± 0.6 vol % for sevoflurane, and mean MACawake was 1.0 ± 0.1 vol % for isoflurane and 1.3 ± 0.3 vol % for sevoflurane.
Conclusions and Clinical Relevance—Sevoflurane resulted in a more rapid induction than did isoflurane. The MACawake for dogs was higher than values reported for both agents in humans. Care should be taken to ensure that dogs are at an appropriate anesthetic depth to prevent consciousness, particularly when single-agent inhalant anesthesia is used.
Objective—To determine the effect of dexmedetomidine, morphine-lidocaine-ketamine (MLK), and dexmedetomidine-morphine-lidocaine-ketamine (DMLK) constant rate infusions on the minimum alveolar concentration (MAC) of isoflurane and bispectral index (BIS) in dogs.
Animals—6 healthy adult dogs.
Procedures—Each dog was anesthetized 4 times with a 7-day washout period between anesthetic episodes. During the first anesthetic episode, the MAC of isoflurane (baseline) was established. During the 3 subsequent anesthetic episodes, the MAC of isoflurane was determined following constant rate infusion of dexmedetomidine (0.5 μg/kg/h), MLK (morphine, 0.2 mg/kg/h; lidocaine, 3 mg/kg/h; and ketamine, 0.6 mg/kg/h), or DMLK (dexmedetomidine, 0.5 μg/kg/h; morphine, 0.2 mg/kg/h; lidocaine, 3 mg/kg/h; and ketamine 0.6 mg/kg/h). Among treatments, MAC of isoflurane was compared by means of a Friedman test with Conover posttest comparisons, and heart rate, direct arterial pressures, cardiac output, body temperature, inspired and expired gas concentrations, arterial blood gas values, and BIS were compared with repeated-measures ANOVA and a Dunn test for multiple comparisons.
Results—Infusion of dexmedetomidine, MLK, and DMLK decreased the MAC of isoflurane from baseline by 30%, 55%, and 90%, respectively. Mean heart rates during dexmedetomidine and DMLK treatments was lower than that during MLK treatment. Compared with baseline values, mean heart rate decreased for all treatments, arterial pressure increased for the DMLK treatment, cardiac output decreased for the dexmedetomidine treatment, and BIS increased for the MLK and DMLK treatments. Time to extubation and sternal recumbency did not differ among treatments.
Conclusions and Clinical Relevance—Infusion of dexmedetomidine, MLK, or DMLK reduced the MAC of isoflurane in dogs. (Am J Vet Res 2013;74:963–970)
OBJECTIVE To determine the pharmacokinetic and pharmacodynamic effects of midazolam following IV and IM administration in sheep.
ANIMALS 8 healthy adult rams.
PROCEDURES Sheep were administered midazolam (0.5 mg/kg) by the IV route and then by the IM route 7 days later in a crossover study. Physiologic and behavioral variables were assessed and blood samples collected for determination of plasma midazolam and 1-hydroxymidazolam (primary midazolam metabolite) concentrations immediately before (baseline) and at predetermined times for 1,440 minutes after midazolam administration. Pharmacokinetic parameters were calculated by compartmental and noncompartmental methods.
RESULTS Following IV administration, midazolam was rapidly and extensively distributed and rapidly eliminated; mean ± SD apparent volume of distribution, elimination half-life, clearance, and area under the concentration-time curve were 838 ± 330 mL/kg, 0.79 ± 0.44 hours, 1,272 ± 310 mL/h/kg, and 423 ± 143 h·ng/mL, respectively. Following IM administration, midazolam was rapidly absorbed and bioavailability was high; mean ± SD maximum plasma concentration, time to maximum plasma concentration, area under the concentration-time curve, and bioavailability were 820 ± 268 ng/mL, 0.46 ± 0.26 hours, 1,396 ± 463 h·ng/mL, and 352 ± 148%, respectively. Respiratory rate was transiently decreased from baseline for 15 minutes after IV administration. Times to peak sedation and ataxia after IV administration were less than those after IM administration.
CONCLUSIONS AND CLINICAL RELEVANCE Results indicated midazolam was a suitable short-duration sedative for sheep, and IM administration may be a viable alternative when IV administration is not possible.