Preliminary evaluation of aqueous tear production in dogs after sedation with intramuscular dexmedetomidine-butorphanol combination

Objective. The aims of the study are to evaluate the effect of dexmedetomidine-butorphanol combination on aqueous tear production assessed with Schirmer tear test I (STT I) in dogs and to evaluate the influence of gender, weight, duration of sedation and right or left eye on STT I values after the sedation. Materials and Methods. One hundred forty-one client-owned dogs undergoing clinic visit, radiologic or ultrasonographic assessments, aged > 12 months, without previous ocular disease and with no drug therapy or sedation or anesthesia in the previous three months are included. Ocular examination consists of STT I and an exam with a slit lamp executed before sedation. The same experienced veterinarian performed ocular examination. Dogs with STT I lower than 15 mm/min or higher than 25 mm/min or with abnormalities of the ocular surface were withdrawn from the study. The dogs were sedated with dexmedetomidine 5 μg/kg combined with butorphanol 0.2 mg/kg inoculated intramuscularly (IM). Dexmedetomidine was completely reversed by administering atipamezole IM. The STT I was detected for each dog before sedation, at 15 minutes after the administration of the dexmedetomidine-butorphanol combination and at 15 minutes after the injection of atipamezole at the end of procedure. The data were analysed using ANOVA by means of the general linear model (GLM). STT I values were reported as least-squares means (LSMeans) ± standard error (SE). Age, weight and duration of sedation were expressed as mean ± standard deviation (SD). P values < 0.05 were considered significant. Results. Forty-three dogs are withdrawn from the study because of ocular surface abnormalities or STT I < 15 mm/min or STT I > 25 mm/min. The 98 dogs included in the study (16 entire females, 31 spayed females, 28 entire males and 23 neutered males) belonged to thirty-three breeds, had a mean age of 5.2 ± 2.8 years with a range of 1-11 years and a mean weight of 18.21 ± 9.66 kg with a range of 6-66 kg. STT I before sedation was 21.53 ± 0.24. Mean duration of sedation was 52.57 ± 11.41 minutes with a range of 30-87 minutes. All dogs recovered the walking ability at 15 minutes after the administration of atipamezole. STT I significantly decreased at 15 minutes after sedation (10.03 ± 0.24). At 15 minutes after injection of atipamezole, STT I was significantly higher (14.05 ± 0.24) compared to STT I at 15 minutes after sedation, but it was significantly lower compared to values before sedation. No differences related to breed, sex, right or left eye and body weight are recorded. Conclusions and clinical significance. Dexmedetomidine-butorphanol combination significantly reduces aqueous tear production in dogs. The administration of atipamezole increases tear production, but STT I values stay below 15 mm/min even if dogs are able to walk. Therefore, the use of tear substitutes are recommended just before the sedation and in the hours following the recovery.