Avaliação da pressão intraocular e do diâmetro pupilar em gatos saudáveis anestesiados com isoflurano e pré-medicados com acepromazina isoladamente ou em combinação com tramadol

Abstract

The objective was to to determine possible changes on intraocular pressure (IOP) and pupil diameter (PD) in healthy cats anesthetized with isoflurane, and premedicated with acepromazine alone or in combination acepromazine/tramadol. Thirty cats were randomly allocated into two groups (n=15/each) and intramuscular acepromazine (AG) or acepromazine combined with tramadol (ATG) were injected. PD (electronic caliper), IOP (rebound tonometry) and mean arterial pressure (MAP) (oscillometric) were assessed before (baseline) and following 30 (PM1), and 40 minutes (PM2) of treatments. Afterwards, anesthesia was induced with propofol, and once the animals had achieved the surgical anesthetic plane (end-tidal concentration of isoflurane set at 2.0%), IOP, DP, MAP, heart and respiratory rates, end-tidal partial concentration of CO2, and peripheral oxygen saturation were recorded (A10) at each 10 minutes until the end of anesthesia (A40). IOP decreased in both AG (P=0.008) and ATG (P=0.0001), when comparing values assessed at baseline with PM1. IOP decreased (P=0.021) only in AG, in comparisons between baseline and PM2. During anesthesia, IOP did not differ within each group (P>0.05). In comparisons between groups, such parameter did not change at any time point before and after induction of anesthesia (P>0.05). Comparisons between baseline values with the ones recorded at PM1 and 2 showed that PD increased 1.45 (P=0.015) and 1.89 mm (P=0.009), respectively, in cats of ATG. After anesthesia was induced, PD of cats decreased in both AG (P<0.0001) and ATG (P<0.01). From A10 until A40, average PD of cats of ATG was 0.66 mm higher than the ones recorded in the eyes of cats of AG (P>0.05). MAP did not change from PM1 to 2, but decreased during anesthesia when comparing with baseline, PM1, and 2 (P<0.01). From A10 to A40, all the other parameters remained unchanged (P>0.05). It can be concluded that IOP decreased significantly and did not change in healthy cats premedicated with acepromazine alone or in combination with tramadol during isoflurane anesthesia. Animals of the acepromazine/tramadol groups had higher values of pupil diameter throughout the experiment than those submitted only with acepromazine alone. However, this parameter was not maintained throughout the anesthetic period and could not inhibit the occurrence of miosis. However, in order to perform corneal or intraocular surgeries, this anesthetic protocol maintains the reduced and stable intraocular pressure within the reference range for this species, but to obtain even more mydriasis, supplementation with parasympatolytics should be instituted to aid in pupillary dilation.