Abstract
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 (MACISO) in dogs were evaluated. Seven healthy adult dogs were included. Anaesthesia was induced with propofol and maintained with isoflurane. For each dog, baseline MAC (MACISO/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 MACISO 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 MACISO/BASAL. The combination resulted in a greater MACISO 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.
Highlights
The end-tidal partial pressure of inhalant anaesthetics required to prevent movement in 50% of individuals exposed to a supramaximal noxious stimulus represents an index of potency of anaesthetic agents [1]
LIDO, DEX and LIDO-DEX significantly decreased minimum alveolar concentration of isoflurane (MACISO) by 27.3%, 43.4% (33.3–53.3%) and 60.9% (46.1–78.1%) (p = 0.001, p = 0.013, p = 0.013), respectively, when compared to MACISO/ BASAL
The MACISO was significantly lower after LIDO-DEX when compared with LIDO or DEX treatments alone (p = 0.001 and p = 0.013, respectively)
Summary
The end-tidal partial pressure of inhalant anaesthetics required to prevent movement in 50% of individuals exposed to a supramaximal noxious stimulus (i.e. minimum alveolar concentration, MAC) represents an index of potency of anaesthetic agents [1]. The MAC of contemporary inhalant anaesthetics has been previously reported in dogs and after the administration of different opioids, sedatives, tranquilisers and local anaesthetics [2,3,4]. One of the main issues concerning inhalant anaesthesia is the progressive cardiovascular depression related to the delivery of high concentrations. Drugs such as lidocaine (local anaesthetic) and dexmedetomidine (sedative) decrease the MAC of inhaled anaesthetics and may reduce the risk of cardiopulmonary depression by means of decreasing the inhalant anaesthetic requirements during anaesthesia [5,6,7]. Lidocaine decreases the MAC of inhaled anaesthetics by
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