Lidocaine, Dexmedetomidine and Their Combination Reduce Isoflurane Minimum Alveolar Concentration in Dogs

The effects of intravenous (IV) lidocaine, dexmedetomidine and their combination delivered as a bolus followed by a constant rate infusion (CRI) on the minimum alveolar concentration of isoflurane (MAC(ISO)) in dogs were evaluated. Seven healthy adult dogs were included. Anaesthesia was induced with propofol and maintained with isoflurane. For each dog, baseline MAC (MAC(ISO/BASAL)) was determined after a 90-minute equilibration period. Thereafter, each dog received one of the following treatments (loading dose, CRI): lidocaine 2 mg kg(−1), 100 µg kg(−1) minute(−1); dexmedetomidine 2 µg kg(−1), 2 µg kg(−1) hour(−1); or their combination. MAC was then determined again after 45- minutes of treatment by CRI. At the doses administered, lidocaine, dexmedetomidine and their combination significantly reduced MAC(ISO) by 27.3% (range: 12.5–39.2%), 43.4% (33.3–53.3%) and 60.9% (46.1–78.1%), respectively, when compared to MAC(ISO)/(BASAL). The combination resulted in a greater MAC(ISO) reduction than the two drugs alone. Their use, at the doses studied, provides a clinically important reduction in the concentration of ISO during anaesthesia in dogs.