Reliability of three scoring systems for assessing quality of anaesthetic induction in horses

Several induction quality scoring systems (IQSS) have been described to evaluate drugs and risk factors of this anaesthetic period in horses, but no attempts to compare their reliability have been performed.

To elucidate the reliability of three IQSS: the visual analogue scale (VAS), a simple descriptive scale (SDS), and a composite grading scale (CGS) proposed by the authors.

Reliability study.

Eight randomly selected video-recorded anaesthetic inductions from horses that underwent general anaesthesia were evaluated twice by four blinded evaluators with experience in equine anaesthesia, with a 1-month interval between assessments using the three aforementioned IQSS. A total of 64 evaluations per scale were generated. To assess reliability, intra- and inter-rater intraclass correlation coefficient (ICC), and their 95% confidence intervals (CI) were calculated based on a mean rating (k = 4), absolute agreement, 2-way random-effects model.

The inter-rater agreement was classified as moderate to good inter-rater reliability for all the scales, with the highest ICC found for the VAS (0.74 ± 0.11), followed by the CGS and the SDS (0.65 ± 0.22 and 0.63 ± 0.21, respectively). Intra-rater agreement results demonstrated very good reliability for both VAS and SDS (0.82 ± 0.08; 0.81 ± 0.18, respectively) and excellent reliability for the CGS (0.91 ± 0.08).

The use of video-recordings instead of in situ evaluations, as the absence of audio may affect the assessment. Additionally, these findings are applicable only when free inductions are evaluated.

The VAS and the novel CGS are reliable IQSS in horses, as are the widely used SDS. As the SDS are inconsistent across the literature, the VAS would be advised if multiple evaluators assess induction quality for research purposes, whereas the CGS would be selected for studies involving a single observer. We suggest routine inclusion of the VAS in the evaluation of the anaesthetic induction in horses.