Objective: To evaluate selected effects of midazolam or lidocaine administered prior to etomidate for co-induction of anesthesia in healthy dogs. Study design: Prospective crossover experimental study. Animals: A group of 12 healthy adult female Beagle dogs. Methods: Dogs were premedicated with intravenous (IV) butorphanol (0.3 mg kg–1), and anesthesia was induced with etomidate following midazolam (0.3 mg kg–1), lidocaine (2 mg kg–1) or physiologic saline (1 mL) IV. Heart rate (HR), arterial blood pressure, respiratory rate (fR) and intraocular pressure (IOP) were recorded following butorphanol, after co-induction administration, after etomidate administration and immediately following intubation. Baseline IOP values were also obtained prior to sedation. Etomidate dose requirements and the presence of myoclonus, as well as coughing or gagging during intubation were recorded. Serum cortisol concentrations were measured prior to premedication and 6 hours following etomidate administration. Results: Blood pressure, fR and IOP were similar among treatments. Blood pressure decreased in all treatments following etomidate administration and generally returned to sedated values following intubation. HR increased following intubation with midazolam and lidocaine but remained stable in the saline treatment. The dose of etomidate (median, interquartile range, range) required for intubation was lower following midazolam (2.2, 2.1–2.6, 1.7–4.1 mg kg−1) compared with lidocaine (2.7, 2.4–3.6, 2.2–5.1 mg kg−1, p = 0.012) or saline (3.0, 2.8–3.8, 1.9–5.1 mg kg−1, p = 0.015). Coughing or gagging was less frequent with midazolam compared with saline. Myoclonus was not observed. Changes in serum cortisol concentrations were not different among treatments. Conclusions and clinical relevance: Midazolam administration reduced etomidate dose requirements and improved intubation conditions compared with lidocaine or saline treatments. Neither co-induction agent caused clinically relevant differences in measured cardiopulmonary function, IOP or cortisol concentrations compared with saline in healthy dogs. Apnea was noted in all treatments following the induction of anesthesia and preoxygenation is recommended.
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