Effects of nitrous oxide on IOP and pupillary diameter in dogs anesthetized with varying concentrations of desflurane.

Abstract

OBJECTIVE: The aim of the present study was to evaluate the effects of nitrous oxide on IOP and pupillary diameter (PD) of dogs anesthetized with varying desflurane concentrations. ANIMALS STUDIED: Twenty adult Mongrel dogs were used. METHODS: They were anesthetized with propofol (10 mg/kg, IV) and maintained with varying concentrations of desflurane (1.6, 1.4, and 1.2 MAC) diluted in 100% oxygen (G1) or in 70% nitrous oxide and 30% oxygen (G2) (30 mL/kg/min). IOP was measured by applanation tonometry and horizontal PD was taken with a caliper adjacent to the cornea. Mean arterial pressure (MAP), heart rate (HR), respiratory rate (RR), and end-tidal CO(2) (etCO2) were also measured. All parameters were measured at T0, T30, T45, and T60 time points. One-way repeated measures anova and the t-test were used to assess statistical differences (P < 0.05). RESULTS: T30, T45, and T60 IOP measures were within normal limits for both groups and IOP did not differ between groups at any time. There was a significant decrease in PD in G1 between T0 and T30, T45 and T60, and also between T30 and T60. PD did not differ between groups. All vital parameters were within normal limits throughout anesthesia. CONCLUSIONS: Administration of nitrous oxide with desflurane results in maintenance of normal IOP and prevents a decrease in horizontal PD during anesthesia. Therefore, this may be a suitable protocol in dogs undergoing intraocular surgeries that require mydriasis and maintenance of normal IOP.