Effect of propofol and ketamine-diazepam on intraocular pressure in healthy premedicated dogs

Objective: To compare the effect of propofol and ketamine/diazepam for induction following premedication on intraocular pressure (IOP) in healthy dogs.

Study design: Prospective, quasi-experimental, unmasked, longitudinal.

Animals: A total of 61 client-owned dogs.

Methods: Dogs were anesthetized twice with a 4 week washout period. Premedication with dexmedetomidine (5 μg kg^-1) and hydromorphone (0.1 mg kg^-1) intramuscularly was followed by either propofol (4 mg kg^-1) or ketamine (5 mg kg^-1) and diazepam (0.25 mg kg^-1) intravenously for induction and inhaled isoflurane for maintenance. IOP was measured by applanation tonometry using TonoPen-XL before premedication and after 5, 10, 20 and 30 minutes. IOP was measured again immediately after induction and after 3, 5, 10, 15, 20, 30 and 40 minutes. Data were analyzed using one- or two-way repeated measures ANOVA.

Results: No difference was found between right and left IOP (p = 0.45), and data from both the eyes of each dog were averaged and considered as one set of data. Following premedication, IOP was significantly lower at all time points than at baseline when animals were grouped together, mean difference -1.6 ± 0.2 mmHg (p < 0.05). IOP increased immediately (12.2 ± 2.4 mmHg before versus 17.1 ± 3.8 mmHg after) and at 3, 5 (p < 0.001), 10 and 40 minutes (p = 0.009 and 0.045, respectively) after propofol administration. For ketamine/diazepam, IOP was increased immediately post-induction (13.0 ± 2.7 mmHg before versus 14.7 ± 2.8 mmHg after) and at 3, 5 (p < 0.001), 30 and 40 minutes (p = 0.010 and 0.037, respectively).

Conclusions and clinical relevance: Sedation with hydromorphone and dexmedetomidine significantly decreased IOP in normal dogs and may be an appropriate choice for dogs that cannot tolerate acute increases in IOP. However, IOP increased significantly after both induction protocols, abolishing the effect of premedication.