Preoperative risk assessment in horses: agreement and predictive value of CHARIOT (Combined Horse Anaesthetic Risk Identification and Optimisation Tool).

Overview

• This research evaluates the agreement and predictive accuracy of a preoperative risk assessment tool, CHARIOT, for horses undergoing anesthesia, comparing it with the established ASA-PS system across evaluators of varying expertise.
• It also investigates the relationship between risk scores from these tools and the likelihood of mortality within 7 days after surgery.

Introduction to the Study

• Purpose: To compare the Combined Horse Anaesthetic Risk Identification and Optimisation Tool (CHARIOT) with the American Society of Anesthesiologists Physical Status (ASA-PS) classification system in predicting postoperative mortality in horses.
• Context: Preoperative risk assessment is crucial for planning anesthesia and managing perioperative risks in horses.
• Motivation: CHARIOT integrates several factors aimed to optimize risk identification but its reliability and predictive value compared to the traditional ASA-PS system needed evaluation.

Study Design and Methods

• Type of Study: Prospective, observational, single-centre pilot study.
• Subjects: 50 client-owned horses scheduled for general anesthesia.
• Evaluators: Five different groups performed risk assessments independently for each horse:
  • Equine rotating interns
  • Residents of the European College of Veterinary Anaesthesia and Analgesia (ECVAA)
  • Anaesthesia experts (ECVAA Diplomates or residency-trained)
  • Equine residents from surgery or internal medicine specialties (ECVS or ECEIM)
  • European Board of Veterinary Specialisation Specialists (ECVS or ECEIM Diplomates)
• Assessment Tools: Each evaluator assigned two scores per horse:
  • ASA-PS score (standard physical status classification)
  • CHARIOT score (combined new risk identification tool)
• Statistical Analysis:
  • Mixed-effects Poisson regression to compare scores between evaluator groups and scoring systems.
  • Pairwise comparisons to determine significant differences between evaluator types.
  • Logistic regression and receiver operating characteristic (ROC) curve analysis to assess how well scores predicted 7-day postoperative mortality.

Key Findings

• Score Differences Among Evaluators:
  • Anaesthesia experts assigned higher average scores (ASA-PS ~2, CHARIOT ~13.9) than other groups.
  • Interns, equine residents, and EBVS specialists tended to assign lower scores compared to anaesthesia experts and residents.
  • Statistically significant higher scoring was noted in ECVAA residents and experts compared to all other groups (p < 0.05).
• Association with Mortality:
  • Both CHARIOT and ASA-PS scores were positively correlated with the odds of mortality within 7 days after surgery (p < 0.001).
  • Higher risk scores predicted higher chances of postoperative death, suggesting both tools have predictive value.

Interpretation and Implications

• Anaesthesia experts provided more conservative (higher) risk assessments, potentially reflecting greater sensitivity or experience regarding anesthetic risks in horses.
• The CHARIOT tool performs similarly to the ASA-PS system in predicting short-term postoperative mortality but may incorporate a broader range of risk factors.
• Consistency across evaluator types varied, indicating that expertise influences risk assessment scoring, which is important when implementing such tools clinically.
• These findings support the use of structured scoring systems like CHARIOT for preoperative risk evaluation but highlight the need for training and standardization among evaluators.

Study Limitations and Future Directions

• Single-centre pilot study with a relatively small sample size limits generalizability.
• Further multi-centre studies are recommended to:
  • Validate CHARIOT’s predictive accuracy in diverse clinical settings.
  • Refine the scoring criteria and application protocols to improve interobserver agreement.
  • Assess long-term outcomes beyond the initial 7-day postoperative period.

Conclusions

• CHARIOT is a promising tool for assessing anesthetic risk in horses, showing comparable predictive value to the established ASA-PS system.
• Anaesthesia experts tend to assign higher risk scores, perhaps reflecting deeper understanding or caution.
• Higher preoperative scores correlate significantly with increased risk of mortality shortly after surgery.
• Additional research with larger and varied populations will help confirm these findings and optimize clinical use of CHARIOT.