Measurement of intraocular pressure in healthy anesthetized horses during hoisting

To measure intraocular pressure (IOP) in horses during hoisting after induction of anesthesia.

Prospective nonrandomized clinical study.

Eighteen healthy adult horses aged [mean±standard deviation (SD)] 10±4.2 years and weighing 491±110 kg anesthetized for elective procedures.

IOP was measured in the superior eye of each horse based on planned recumbency after induction of anesthesia. Measurements were taken directly after premedication with xylazine or detomidine with butorphanol, after induction with diazepam-ketamine, after intubation, when suspended by the hoist and on the operating table. During hoisting, the head was supported and the eye-heart height was measured to account for variations in head positioning among patients. IOPs were compared across time points using repeated-measures analysis of variance. Regression was used to compare IOP outcome with potential cofactors.

Compared with measurements after premedication (17.5±2.5 mmHg) (mean±SD), hoisting significantly increased IOP (32.4±15.3 mmHg) (p<0.01). The highest recorded IOP in the hoist was 80.0 (range, 16.0-80.0) mmHg. The difference in IOP between premedication and hoisting was 15.0±16.2 (range, -1.0 to 68.0) mmHg. Body weight had a significant effect on absolute IOP and change in IOP in the hoist (p<0.01).

Hoist IOP was significantly higher than post-premedication IOP with heavier horses having higher hoist IOPs and greater increases in IOP. The clinician should take this relationship into account when anesthetizing and hoisting larger horses where an increase in IOP could be detrimental.