Intraocular pressure following four different intravenous sedation protocols in normal horses.
Authors: Joyner Rebekah L, Liu Chin-Chi, Cremer Jeannette, Carter Renee T, Lewin Andrew C
Journal: Equine veterinary journal
Summary
# Editorial Summary: Sedation and Intraocular Pressure in Horses Effective sedation is standard practice during equine ophthalmic examination, yet the comparative effects of commonly used protocols on intraocular pressure (IOP) remained unclear until this 2021 research. The authors tested four standing sedation regimens across twelve horses in a randomised cross-over design: xylazine with butorphanol, detomidine with butorphanol, detomidine alone, and xylazine alone, measuring IOP before and at five time points up to 60 minutes post-administration. All protocols reduced IOP from a baseline of 21.8 mm Hg, with maximum reduction occurring at five minutes, though the detomidine-butorphanol combination proved superior—achieving 14.5 mm Hg compared to 16.3–17.1 mm Hg for other treatments. Significantly, detomidine monotherapy produced less consistent IOP reduction across the measurement period than combined protocols, and head position materially affected readings, with dependent head positioning yielding substantially higher pressures than the elevated position used for baseline measurements. For practitioners performing tonometry in sedated horses, these findings support the use of detomidine-butorphanol combinations for optimal IOP reduction during ophthalmic work, whilst emphasising that standardising head height between baseline and post-sedation measurements is essential for valid pressure comparisons.
Read the full abstract on PubMed
Practical Takeaways
- •If performing ophthalmic exams requiring sedation, use detomidine (10 µg/kg) combined with butorphanol (0.01 mg/kg) for optimal IOP reduction within the first 5 minutes
- •Avoid using detomidine as a standalone sedative if IOP reduction is clinically important, as it produces less effective reduction
- •Standardize head position when measuring IOP in horses for consistent, comparable results—maintain consistent head elevation relative to baseline measurements
Key Findings
- •All four sedation protocols reduced intraocular pressure (IOP) compared to baseline (21.8 mm Hg), with greatest reduction at 5 minutes post-sedation
- •Detomidine 10 µg/kg with butorphanol 0.01 mg/kg (SED2) produced the lowest IOP at 5 minutes (14.5 mm Hg), significantly greater reduction than other protocols
- •Detomidine alone (SED3) produced less pronounced IOP reduction and higher readings across all time points compared to other treatments
- •Head position during IOP measurement significantly affects readings, with head-elevated position yielding lower values than head-down position (P<0.001)