Effects of morphine-alfaxalone-midazolam premedication, alfaxalone induction and sevoflurane maintenance on intraocular pressure and tear production in dogs

Abstract

Intraocular pressure (IOP) and tear production are ocular parameters commonly affected by general anaesthesia. A good control of both of them is necessary to guarantee a successful ophthalmic surgery. The purpose of this research was to analyse the effect of a common anaesthetic protocol based on morphine-alfaxalone-midazolam premedication, alfaxalone induction and sevoflurane maintenance on IOP and Schirmer tear test (STT-1) in healthy dogs. Twenty two adult mixed dogs scheduled for an ovariohysterectomy were used for this study. IOP and STT-1 were registered at baseline (T0), 5 (T1), 10 (T2) and 15 (T3) minutes after premedication with morphine-alfaxalone-midazolam combination; after induction (T4) with alfaxalone and 15 (T5) and 25 (T6) minutes after maintenance with sevoflurane. A paired Student´s t-test and a Wilcoxon test were used to analyse the difference between IOP and STT-1 over time respectively. This anaesthetic protocol produced a statistically significant increase in IOP (P<0.05) after premedication and induction, which was maintained after intubation. STT-1 showed a severe significant reduction during all the procedure (P<0.001). These conclusions should be taken into consideration, especially in dogs with damaged corneas, those predisposed to glaucoma and those who will be undergoing intraocular surgery. Ocular lubrication is necessary if this protocol is used.