Construct validity, responsiveness and reliability of the Feline Grimace Scale in kittens

Abstract

Objectives The aim of the present study was to investigate the construct validity, responsiveness and reliability of the Feline Grimace Scale (FGS) in kittens. Methods A total of 36 healthy female kittens (aged 10 weeks to 6 months) were included in a prospective, randomized, blinded study. Video recordings of all kittens were made before and 1 and 2 h after ovariohysterectomy using an opioid-free injectable anesthetic protocol with or without multimodal analgesia. Additional recordings were taken before and 1 h after administration of rescue analgesia (buprenorphine 0.02 mg/kg IM) to painful kittens. Screenshots of facial images were collected from the video recordings for FGS scoring. Four observers blinded to treatment groups and time points scored 111 randomized images twice with a 5-week interval using the FGS. Five action units (AUs) were scored (ear position, orbital tightening, muzzle tension, whiskers position and head position; 0–2 each). Construct validity, responsiveness, and inter- and intra-rater reliability were evaluated using linear models with Benjamini–Hochberg correction, Wilcoxon signed-rank test and single intraclass correlation coefficients (ICCsingle), respectively ( P <0.05). Results FGS total ratio scores were higher at 1 and 2 h after ovariohysterectomy (median [interquartile range, IQR]: 0.30 [0.20–0.40] and 0.30 [0.20–0.40], respectively) than at baseline (median [IQR]: 0.10 [0.00–0.30]) ( P <0.001). FGS total ratio scores were lower after the administration of rescue analgesia (median [IQR] before and after rescue analgesia) 0.40 [0.20–0.50] and 0.20 [0.10–0.38], respectively ( P <0.001). Inter-rater ICCsingle was 0.68 for the FGS total ratio scores and 0.35–0.70 for all AUs considered individually. Intra-rater ICCsingle was 0.77–0.91 for the FGS total ratio scores and 0.55–1.00 for all AUs considered individually. Conclusions and relevance The FGS is a valid and responsive acute pain-scoring instrument with moderate inter-rater reliability and good to excellent intra-rater reliability in kittens.