Effects of anesthetic induction with midazolam-propofol and midazolam-etomidate on selected ocular and cardiorespiratory variables in clinically normal dogs.

OBJECTIVE: To compare effects of anesthetic induction with midazolam-propofol or midazolam-etomidate on intraocular pressure (IOP), pupillary diameter (PD), pulse rate, blood pressure, and respiratory rate in clinically normal dogs. ANIMALS: 18 dogs. PROCEDURES: Dogs undergoing ophthalmic surgery received midazolam (0.2 mg/kg, IV) and either propofol or etomidate (IV) until intubatable. For all dogs, results of physical examinations, ophthalmic examinations of the nonoperated eye, and preanesthetic blood analyses were normal. Intraocular pressure, PD, blood pressure, pulse rate, and respiratory rate were measured in the nonoperated eye at 5 time points: just prior to the anesthetic induction sequence, after 5 minutes of preanesthetic oxygenation via face mask, after IV administration of midazolam, after IV anesthetic induction, and after endotracheal intubation.
RESULTS: PD decreased significantly from baseline by 4.4 ± 0.4 mm (mean ± SD) after anesthetic induction and 5.3 ± 0.4 mm after intubation in the etomidate group and by 1. 2 ± 0.4 mm after intubation in the propofol group. Intraocular pressure was increased significantly from baseline by 3.2 ± 1.0 mm Hg after anesthetic induction in the etomidate group and by 4.7 ± 1.2 mm Hg after anesthetic induction and 4.5 ± 1. 2 mm Hg after intubation in the propofol group. Pulse rate was significantly lower by 28.6 ± 12.6 beats/min after anesthetic induction in the etomidate group, compared with the propofol group. CONCLUSIONS AND CLINICAL RELEVANCE: At the studied doses, midazolam-etomidate caused clinically important miosis and increased IOP. Midazolam-propofol caused an even greater increase in IOP but had minimal effects on PD.