1. Effects of diazepam and flumazenil on minimum alveolar concentrations for dogs anesthetized with isoflurane or a combination of isoflurane and fentanyl.
- Author
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Hellyer PW, Mama KR, Shafford HL, Wagner AE, and Kollias-Baker C
- Subjects
- Adjuvants, Anesthesia blood, Anesthetics, Inhalation pharmacology, Animals, Anti-Anxiety Agents antagonists & inhibitors, Anti-Anxiety Agents blood, Blood Pressure drug effects, Body Temperature drug effects, Diazepam blood, Drug Interactions, Female, Fentanyl antagonists & inhibitors, Fentanyl blood, Flumazenil blood, Flumazenil pharmacology, GABA Modulators blood, GABA Modulators pharmacology, Heart Rate drug effects, Isoflurane pharmacology, Pulmonary Alveoli drug effects, Adjuvants, Anesthesia pharmacology, Anesthetics, Inhalation pharmacokinetics, Anti-Anxiety Agents pharmacology, Diazepam pharmacology, Dogs metabolism, Fentanyl pharmacology, Isoflurane pharmacokinetics, Pulmonary Alveoli metabolism
- Abstract
Objective: To determine the effect of a constant-rate infusion of fentanyl on minimum alveolar concentration (MAC) of isoflurane and to determine the interaction between fentanyl and a benzodiazepine agonist (diazepam) and antagonist (flumazenil) in isoflurane-anesthetized dogs., Animals: 8 mixed-breed adult dogs., Procedure: Dogs were anesthetized with isoflurane 3 times during a 6-week period. After a 30-minute equilibration period, each MAC determination was performed in triplicate, using standard techniques. Fentanyl was administered as a bolus (10 microg/kg of body weight, IV) that was followed by a constant infusion (0.3 microg/kg per min, IV) throughout the remainder of the experiment. After determining isoflurane-fentanyl MAC in triplicate, each dog received saline (0.9% NaCl) solution, diazepam, or flumazenil. After 30 minutes, MAC was determined again., Results: Fentanyl significantly decreased isoflurane MAC (corrected to a barometric pressure of 760 mm Hg) from 1.80+/-0.21 to 0.85+/-0.14%, a reduction of 53%. Isoflurane-fentanyl-diazepam MAC (0.48+/-0.29%) was significantly less than isoflurane-fentanyl-saline MAC (0.79+/-0.21%). Percentage reduction in isoflurane MAC was significantly greater for fentanyl-diazepam (74%), compared with fentanyl-saline (54%) or fentanyl-flumazenil (61%). Mean fentanyl concentrations for the entire experiment were increased over time and were higher in the diazepam group than the saline or flumazenil groups., Conclusions and Clinical Relevance: Fentanyl markedly decreased isoflurane MAC in dogs. Diazepam, but not flumazenil, further decreased isoflurane-fentanyl MAC. Our results indicate that diazepam enhances, whereas flumazenil does not affect, opioid-induced CNS depression and, possibly, analgesia in dogs. more...
- Published
- 2001
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