Intraoperative Mechanical Power and Post-Anesthetic Respiratory Outcomes in Horses: A Retrospective Cohort Study.

Overview

• This study investigates how the mechanical power delivered by ventilators during anesthesia affects respiratory outcomes in horses after surgery.
• The research found that higher mechanical power during anesthesia is linked to poorer oxygen levels during recovery, indicating potential respiratory complications.

Introduction to the Research Topic

• Mechanical Power (MP): A comprehensive measure of the energy delivered to the lungs by the ventilator during anesthesia, combining various respiratory parameters into one value.
• Clinical Importance in Humans: MP has been associated with lung injury caused by ventilators and complications after ventilation.
• Gap in Veterinary Medicine: The role of MP in veterinary anesthesia, specifically in horses, had not been clearly defined before this study.

Research Objective

• To determine if intraoperative MP correlates with post-anesthetic respiratory outcomes, particularly oxygen saturation (SpO₂) during recovery in horses undergoing inhalant anesthesia.

Methods

• Study Design: Retrospective cohort study analyzing data from 843 adult horses anesthetized from 2023 to 2024.
• Data Collection: Anesthesia records were reviewed to calculate the mechanical power administered to each horse.
• Grouping: Horses were divided based on their recovery oxygen saturation:
  • Group L: Low recovery SpO₂ (<95%)
  • Group N: Normal recovery SpO₂ (≥95%)
• Analysis: Multivariable logistic regression was used to examine the relationship between MP and the risk of low oxygen saturation during recovery, adjusting for potential confounders.

Key Results

• Mechanical Power Differences: Horses in the low oxygen saturation group (Group L) had significantly higher intraoperative MP (100.9 ± 36.4 J/min) compared to the normal group (83.6 ± 30.2 J/min), with a strong statistical significance (P < 0.001).
• Normalization: This difference remained even after adjusting MP by the horse’s body weight, ensuring body size did not skew results.
• Risk Assessment: Each 0.02 J/kg/min increment in MP increased the odds of low recovery SpO₂ by 24% (adjusted odds ratio 1.24; 95% confidence interval: 1.12 to 1.38; P < 0.001).
• Other Findings: Higher MP was also associated with:
  • Greater severity of hypoxemia (low blood oxygen levels).
  • Development of postoperative pneumonia, though this occurred infrequently (1.3% incidence).

Conclusions and Implications

• Delivers evidence that higher mechanical power during anesthesia is linked to impaired oxygenation during recovery in horses.
• MP may be used as a marker of ventilatory intensity that can predict or indicate risks of respiratory complications post-anesthesia.
• Supports the need for future prospective studies to:
  • Confirm these associations in a controlled manner.
  • Define clinically relevant MP thresholds to improve ventilatory management during equine anesthesia.