Canine intraocular pressure dynamics during mild-pain ophthalmic procedures in three premedication protocols

Maintaining intraocular pressure (IOP) stability during ophthalmic procedures is essential to ensuring surgical success and reducing complications related to IOP fluctuations. This study aimed to evaluate IOP dynamics in dogs undergoing mild-pain ophthalmic procedures under three different premedication protocols: butorphanol alone (B), butorphanol with medetomidine (BM), and butorphanol with acepromazine (BA).

Thirty clinically healthy client-owned dogs of various breeds (19 males, 11 females, aged 4 months-11 years, weight 7.8-79 kg) were randomized into three groups. IOP was measured at multiple perioperative time points using rebound tonometry: premedication (T0), 5 (T5), and 10 (T10) min after premedication, after intubation (Tint), before surgery (Tbsur), post-surgery (Tasur), during extubation (Text), and before discharge (Tlea). Statistical analyses, including t-tests and Pearson correlation, were performed to assess differences in IOP within and between groups.

Significant changes in IOP were observed at different time points across groups. The B group showed a significant IOP increase between T0 (15.55 ± 3.50 mmHg) and Tint (19.3 ± 4.19 mmHg) (p < 0.05). In the BM group, IOP increased from T0 (15.9 ± 2.77 mmHg) to Tint (19.15 ± 4.52 mmHg) and decreased significantly postoperatively at Tasur (13.5 ± 3.50 mmHg). The BA group exhibited significant IOP reductions from T0 (20.35 ± 2.78 mmHg) to Tbsur (16.45 ± 3.97 mmHg) and Tlea (17.15 ± 4.22 mmHg). No correlation was found between IOP and sex, breed, or age.

IOP remained within normal ranges throughout the perioperative period in all groups. Acepromazine, in combination with butorphanol, was the most effective in attenuating the IOP increase caused by intubation, suggesting its potential advantage in patients at risk of corneal perforation. Clinically, premedication selection should prioritize minimal IOP fluctuation to enhance surgical outcomes.