Decreased tear production associated with general anesthesia in the horse.

The study reveals that horses experience decreased tear production when under general anesthesia, specifically when maintained with halothane in oxygen. However, the tear production normalizes three hours after discontinuing the anesthesia.

Study Design and Methodology

• The study involved 14 horses on which Schirmer I tear tests were performed to monitor the tear production. The Schirmer I tear test is a common clinical procedure used to measure tear production, usually performed by placing a standardized strip of absorbent paper in the lower conjunctival sac.
• The researchers conducted the test at different stages– before and after the intravenous administration of xylazine hydrochloride, during maintenance anesthesia with halothane in oxygen, and three hours following the discontinuation of anesthesia.

Key Findings and Observations

• The administration of xylazine hydrochloride, a drug often used for sedation, analgesia and muscle relaxation in horses, did not decrease tear production. The mean base-line tear production remained at 23.94 +/- 5.23 mm/min after the administration of this drug.
• During the maintenance of halothane anesthesia, tear production was observed to decrease. At 30 minutes it had a mean value of 15.57 +/- 4.29 mm/min and further dropped to 13.84 +/- 4.25 mm/min at 60 minutes. Halothane is a potent inhalational anesthetic and its use in this study was associated with decreased tear production in horses.
• Significantly, three hours after discontinuing the anesthesia, the tear production in horses returned to near normal levels with a mean value of 22.58 +/- 4.12 mm/min. This indicates that the effect of halothane anesthesia on tear production is temporary.

Conclusion

• The research concludes that general anesthesia, specifically when maintained with halothane in oxygen, can lead to decreased tear production in horses. However, this effect is not permanent and tear production normalizes within a few hours after discontinuing the anesthesia.