Evaluation of sedation depth and quality of performed procedures following administration of α2-agonists combined or not with butorphanol in horses.

Several molecules available in equine medicine provide profound sedation and good analgesia when performing diagnostic or surgical procedures. They differ slightly in degree of action, as well in time as in depth. The aim of this study was to evaluate the depth of sedation and quality of performing a standardized procedure after injection of an 2-agonist alone or associated with butorphanol.
Horses presented to the Equine Clinic of Liege University from December 2007 to June 2008 for an endoscopic, dental, radiological or ophthalmological examination of which owner and clinician agreed to include the horse in the study were retained. All horses (n=133) were sedated in a randomized double blind fashion using one of the six following protocols: detomidine (D) (0.01mg/kg IV), romifidine (R) (0.04mg/kg IV), or xylazine (X) (0.5mg/kg IV) alone or associated with butorphanol (B) (0.02mg/kg IV).
Stability, head position and the reaction to a stimulus (auditive and visual) were evaluated before the start of the procedure. An overall subjective grade using a 10 cm line scale was given to evaluate sedation depth (ranging from no effect to maximal depth on line) and the quality of the performed procedure (ranging from not realised to ideal examination). For each specific procedure, the same clinician experienced in his particular field evaluated the parameters. Data were related by a variance analysis using SAS system and considered significant if P<0.01.
The used protocols significantly influenced both sedation depth and examination quality. Sedation depth increased significantly when B was added in all the three 2-agonists used (mean ± SD): D: 6.46±0.33; D+B: 7.06±0.37; R: 4.93±0.46; R+B: 7.04±0.45; X: 4.94±0.43; X+B: 7.75±0.40.
Detomidine provided a significantly better quality of the examination compared to romifidine and xylazine. The addiction of butorphanol significantly decreased the examination quality when added to detomidine and increased the quality when combined with romifidine and xylazine. Mean (± SD) of the quality of performed procedures: D: 8.41±0.54; D+B: 6.06±0.64; R: 6.68±0.71; R+B: 7.16±0.67; X: 4.47±0.67; X+B: 4.52±0.64.
Comparison of sedation depth and quality of performed examination revealed an increase in quality of examination scores with increasing depth of sedation until a certain level. As from sedation depths with scores of 8 or more, a decrease in quality of examination was encountered.
This report shows the important effect of butorphanol addition on sedation. However, increasing sedation depth was not necessarily linked to a better quality of procedure, notably due to difficulties in handling strongly sedated horses for the procedures performed in this study.