Evaluation of tear production of dogs following administration of ketamine-xylasine combination

The lacrimal glands of the canine orbit and nictitating membrane produce the aqueous portion of the trilaminar preocular tear film, which acts to protect and to provide nutrients of the cornea. Lacrimal secretions additionally contribute to ocular surface immunity by delivery of secretary immunoglobulins (mostly IgA), albumin, lipocalin, interleukins, and antibacterial compounds such as lysozyme and lactoferrin. Aqueous tears also provide mechanical protection to the cornea as a lubricant that flushes debris and bacteria from the corneal surface (1).Sedatives are commonly used in common ocular examination to decrease stress associates with ocular examination and enhance safety during clinical examinations. Being familiar with the possible effects of these drugs on ocular tear production is important. Several drugs can reduce tear production in cats and dogs and their effects may be immediate or gradual. Sometimes decreased tear production rate may result KCS (Kerato-Conjunctivitis Sicca). Anesthetic and pre-anesthetic agents are known to cause reduction in tear production (2-5). This study was aimed to evaluate possible role of Ketamine and Xylasine combination on tear production of normal dogs. Shirmer tear test (STT) evaluation was the technique used in this evaluation.This study was aimed to investigate the effect of anesthetic combination Ketamine and xylasine on aqueous tear production in clinically normal dogs. Aqueous tear production was measured in millimeters wetting per minute by use of the STT by placing the tear test strip in the ventral conjunctival fornix approximately one-third of the distance from the lateral to medial canthus. After insertion of the test strip, the eyelids were gently held closed until 1 minute had elapsed, at which time the STT was read and recorded.Both left and right eyes were tested during every time point, in a random sequence. The same person administered tear testing for each subject, and prior to each test, the inferior cul-de-sac was gently swabbed with a cotton-tipped applicator to remove accumulated tears and mucus. Tear production was measured at baseline (before anesthetic induction); and at 30, and 60 minutes after injections.Materials and Methods Five male cross-bred dogs of about two years old were used in this study. Prior to the study, complete physical examinations, complete blood counts (CBC) and ophthalmic examinations including, indirect ophthalmoscopy and fluorescein staining of both eyes were performed. Deworming was performed by using of Mebendazole and Praziquantel. STT tear test was performed by inserting standard sterileSchirmer tear test strip in the ventral conjunctival fornix for one minute. Tearing rate was measured as the length of strip in millimeters wettened in 1 min. Baseline STT values were recorded just before administration of sedation.Ketamine and Xylasine were injected intramuscularly and STTs were measured in 30 and 60 minutes after intramuscular injection of sedative combinations.Statistical analysis was performed by using SPSS 16 software, one way ANOVA. Normality was determined by use of the Komogorov-Smirnov test. Data were reported as mean ± Standard Errors and the unit for measurements was mm/min and values of P 0.05 were considered significant.ResultsThe measured STTs ranged between 15-24 mm/min during all the measurements. Mean±SEfor the tear production of the dogs before injections were 21.3±3.1. This amount was 18.2±1.5 and 19.3±1.7 mm/min 30 and 60 minutes after injections respectively. The statistical analysis revealed significant differences between tear production rates of these times. DiscussionThis study was performed to evaluate the effects of relatively new sedative; Xylasine when used in a combination with ketamine, on tear production as measured by STT in clinically normal crossbred dogs. Sedatives are known to have immediate effects on tear secretion of dogs and rabbits. The cornea is particularly vulnerable to injury during episodes of general anesthesia, when the palpebral reflex, corneal reflex, and purposeful movement cannot protect the eye from drying, corneal abrasions, or other direct corneal injury.Results of studies in humans suggest both components of tear production (i.e., reflex and basal components) are decreased during general anesthesia. Basal tear production is significantly reduced in human patients during general anesthesia and suggested that reflex tear production is concurrently decreased because of autonomic depression. Dry corneal epithelium may be easily desquamated and swept away by the normal movement of the eyelids, predisposing patients to painful post-anesthetic abrasions or ulcers of the cornea. It is suggested that a negative correlation between intraoperative tear production and general anesthesiain dogs. Length of anesthesia has been correlated with progressively decreasing tear production in dogs during and after anesthesia,but no causal relationship has been established because of the variety of surgical procedures involved, the variable use of anti-cholinergics and other injectable pre-medications, and the typeof study design used(5). The Results of this study reveal the importance of special cares needed to the tear production rate of dogs restraint or anesthetized using Ketamine and Acepromazine.