Team Examines Methods to Evaluate Horses Recovering from Anesthesia

Nov 17, 2015 / Practitioner Updates

Horses Dr. Clark-Price

Stuart Clark-Price, DVM, MS, DACVIM, DACVAA,  presented these abstracts at the 12th World Congress of Veterinary Anaesthesiology in Kyoto, Japan, in September.

PART 1

Inter-Horse Rater Variability and Intra-Rater Consistency of Independent Raters Using a Subjective 100-Point Composite Scale

Anesthetic recovery of horses is frequently evaluated using subjective composite scales that may have poor repeatability, leading to conclusions of questionable utility. The inter-horse rater variability (index of the homogeneity of responses for an individual horse among raters) should be minimal for an effective subjective scoring system. The objective of this study was to examine inter-horse rater variability and intra-rater consistency of independent raters using a subjective composite scale to evaluate anesthetic recovery quality of horses.

In a prospective study, 12 horses were anesthetized with xylazine, midazolam, and ketamine in a padded equine recovery stall. Horses recovered unassisted and recoveries were video recorded and independently evaluated by seven diplomates of the American College of Veterinary Anesthesia and Analgesia using a 100-point subjective composite scale. A Henze-Zirkler test established the multivariate normality of the rater scores. Inter-horse rater variability was determined using repeated measures ANOVA. Intra-rater consistency was determined graphically. Horses were ordered by their total score for the seven raters. Each rater’s cumulative score was plotted against the ascending total score of the 12 horses.

Overall, raters’ scores of individual horses were significantly different (P<0.01). Specifically scores differed for 43% (9/21) of pairs of raters (P<0.03). Intra-rater scores were generally consistent: A rater who scored a horse below the mean of the other six raters tended to give lower scores for all horses; this resulted in regression lines tending to fan out rather than cross.

These findings suggest that subjective composite scales for evaluation of horses recovering from anesthesia could lead different raters to different conclusions about the recovery status of the horse. Systems that do not rely on subjective data may minimize issues associated with rater subjective factors. Investigation and development of non-subjective methods to evaluate equine recoveries is warranted.    

PART 2

An Objective Assessment System for Evaluation of Horses Recovering from Anesthesia Using Three-Axis Accelerometry

Anesthetic recovery of horses is frequently evaluated using subjective composite scales that may have poor repeatability, leading to conclusions of questionable utility. Development of other methods may eliminate problems associated with subjective systems. Accelerometry is the quantitative determination of acceleration of the body in performance of a task and is used to evaluate various problems in veterinary medicine. The objective of this study was to develop a system using accelerometry for the evaluation of anesthetic recovery of horses.

In a prospective study, 12 horses were anesthetized and a three-axis accelerometer was fixed to a surcingle at the level of the withers. Unassisted recoveries were video recorded. Accelerometry data was used to calculate Vmax [V_max= √(X^2+Y^2+Z^2) where X, Y, and Z are the measured axes in gravities (g)] for each unsuccessful attempt and the successful attempt to stand. Recovery videos were independently viewed by seven diplomates of the American College of Veterinary Anesthesia and Analgesia and scored using a subjective 100-point composite scale. Vmax values and the median visual score for each horse were fitted to a library of nonlinear surface mathematical models by a specific computer program to determine the best fit.

The best fit, via fit statistics and visual verification, was a power model and resulted in derivation of the following equation where a horse’s recovery score (RS) = 9.998 x G0.633 x (ΣG)0.174, where G is the Vmax of the successful attempt to stand and ΣG is the sum of the Vmax of unsuccessful attempts to stand. The RS was constrained to a range of 11 to 100 and categorized by score: excellent (11-30), good (30-50), fair (50-70), poor (70-90), and unacceptable (>90).

The developed system may allow objective assessment and facilitate research for improving the recovery of horses from anesthesia.

Presented by:

Stuart C. Clark-Price, DVM, MS, DACVIM, DACVAA; University of Illinois
Kara M. Lascola, DVM, MS, DACVIM; University of Illinois
Manuel Martin Flores, DVM, DACVAA; Cornell University
Andre C. Shih, DVM, DACVAA; University of Florida
Erik H. Hofmeister, DVM, MA, DACVAA, DECVAA; University of Georgia
Lydia L. Donaldson, VMD, PhD, DACVAA; American College of Veterinary Anesthesia and Analgesia, AnimalScan, LLC
Lysa P. Posner, DVM, DACVAA; North Carolina State University
Reza Seddighi, DVM, PhD, DACVAA; University of Tennessee
David J. Schaeffer, PhD; University of Illinois