Intraoperative mechanical power and post-anesthetic respiratory outcomes in horses: A retrospective cohort study

Mechanical power (MP) represents the ventilatory-delivered energy to the respiratory system, integrating multiple variables into a single parameter. It has been linked to ventilator-induced lung injury and post-ventilation complications in human medicine, while clinical relevance in equine anesthesia remains insufficient.

To evaluate the association between intraoperative mechanical power and postoperative respiratory outcomes in horses undergoing inhalant anesthesia.

This retrospective cohort study analyzed anesthesia records from 843 adult horses anesthetized between 2023 and 2024. MP was calculated for each case. Horses were stratified according to mean recovery oxygen saturation (SpO₂) into low (<95%; Group L) and normal (≥95%; Group N) groups. Multivariable logistic regression was used to assess the association between MP and the risk of low recovery SpO₂.

Horses in Group L exhibited significantly higher intraoperative MP compared with Group N (100.9 ± 36.4 vs 83.6 ± 30.2 J/min; P < 0.001); a difference persisted after normalization to body weight. Each 0.02 J/kg/min increase in MP was independently associated with increased odds of low recovery SpO₂ (adjusted OR 1.24; 95% CI 1.12-1.38; P < 0.001). Higher MP values were also observed in horses with more severe hypoxemia and in those that developed postoperative pneumonia, although the incidence of pneumonia was low (1.3%).

Elevated intraoperative MP is associated with impaired post-anesthetic oxygenation in horses. These findings suggest that MP may serve as a marker of ventilatory intensity associated with impaired recovery oxygenation and support the need for prospective studies to establish clinically relevant thresholds.