A critical evaluation for validation of composite and unidimensional postoperative pain scales in horses.
Authors: Barreto da Rocha Paula, Driessen Bernd, McDonnell Sue M, Hopster Klaus, Zarucco Laura, Gozalo-Marcilla Miguel, Hopster-Iversen Charlotte, Esteves Trindade Pedro Henrique, Gonzaga da Rocha Thamiris Kristine, Taffarel Marilda Onghero, Alonso Bruna Bodini, Schauvliege Stijn, Luna Stelio Pacca Loureiro
Journal: PloS one
Summary
# Editorial Summary Two widely-used equine pain assessment tools—the UHAPS (Unesp-Botucatu Horse Acute Pain Scale) and the Composite Pain Scale (CPS)—underwent rigorous validation testing across 42 horses undergoing orthopaedic and soft tissue surgery, with six independent evaluators scoring 168 video clips at multiple time points (pre-surgery, immediately post-op, post-analgesia, and 24 hours post-op). Whilst both scales demonstrated acceptable intra-observer reliability (0.70–0.97) and good criterion validity when compared against simpler unidimensional scales, significant structural weaknesses emerged: weak associations existed among 50% of UHAPS items and 62% of CPS items, internal consistency was barely acceptable (0.51–0.64), and both scales showed poor sensitivity (43% and 38% respectively) despite adequate specificity. Responsiveness was confirmed—pain scores appropriately increased post-operatively—and rescue analgesia cut-off points were identified as ≥5 for UHAPS and ≥7 for CPS, yet the poor sensitivity means these tools may fail to detect genuine pain in a substantial proportion of cases. For practitioners, this suggests that composite pain scales should be supplemented with clinical observation rather than used as standalone diagnostic instruments, and the profession should anticipate refinement or replacement of these currently suboptimal tools pending further development that eliminates redundant scoring items and improves discriminatory capacity.
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Practical Takeaways
- •Current composite pain scales (UHAPS and CPS) are suboptimal for detecting postoperative pain in horses—use cut-offs of ≥5 (UHAPS) or ≥7 (CPS) for rescue analgesia decisions, but remain alert to false negatives given their poor sensitivity
- •Inter-observer variability is significant; train all staff on consistent pain scale application and consider using unidimensional scales (Visual Analog, Numeric) as supplementary tools for more reliable pain assessment
- •These validated cut-off points provide objective thresholds for when to escalate analgesia, but clinical judgment and repeated assessment are essential because the scales miss approximately 60% of painful horses
Key Findings
- •UHAPS and CPS showed intra-observer reliability of 0.70–0.97 but poor to variable inter-observer reproducibility across evaluators
- •Both composite scales demonstrated high specificity (UHAPS 90%, CPS 79%) but low sensitivity (UHAPS 43%, CPS 38%) for postoperative pain detection
- •Criterion validity was acceptable (Spearman correlation >0.67) across all scales, but internal consistency was minimally acceptable (0.51–0.64)
- •Recommended cut-off points for rescue analgesia were ≥5 for UHAPS and ≥7 for CPS; both scales require refinement or replacement for optimal postoperative pain assessment