Influence of dexmedetomidine-propofol-isoflurane and medetomidine-propofol-isoflurane on intraocular pressure and pupil size in healthy dogs

The present prospective, randomised, double-blinded clinical study was designed to investigate the commonly used anaesthetic combinations of dexmedetomidine-propofol-isoflurane and medetomidine-propofol-isoflurane on intraocular pressure and pupil size in dogs. Forty client-owned healthy dogs with no ocular abnormalities, average body weight of 25.7 ± 13.1 kg (mean ± SD) and aged 3.7 ± 2.7 years, were enrolled. Twenty four males and 16 females were included. Dogs were allocated randomly to receive dexmedetomidine i.v. at 0.005 mg/kg, dexmedetomidine at 0.01 mg/kg, medetomidine at 0.01 mg/kg or medetomidine at 0.02 mg/kg. Ten minutes later anaesthesia was induced in all dogs with propofol and maintained with isoflurane in oxygen-air. Intraocular pressure, pupil size, heart rate, respiratory frequency and arterial blood pressures (SAP, DAP) were measured prior to (baseline) and at 10 (before propofol), 20, 30, 40, 50 and 60 min after dexmedetomidine or medetomidine administration. Oxygen saturation of haemoglobin (SpO2) and end-tidal CO2 concentration (EtCO2) was monitored following anaesthesia induction. Data were analysed using Anderson-Darling and Bartlett's tests for data distribution and homogeneity of variance confirmation and ANOVA followed by Dunnett's tests for multiple comparisons. Changes were considered significant when P < 0.05. Following drug administration, pupil size, heart rate and respiratory frequency decreased significantly within groups, but did not differ between groups. No significant changes in intraocular pressure, SAP and DAP within and between groups, and SpO2 or EtCO2 between groups, were observed. Comparable doses of dexmedetomidine or medetomidine combined with propofol and isoflurane induced reductions in pupil size, respiratory frequency and heart rate, however, without a significant influence on intraocular pressure or arterial blood pressure.