Mechanical Power during General Anesthesia and Postoperative Respiratory Failure: A Multicenter Retrospective Cohort Study

Background: Mechanical power during ventilation estimates the energy delivered to the respiratory system through integrating inspiratory pressures, tidal volume, and respiratory rate into a single value. It has been linked to lung injury and mortality in the acute respiratory distress syndrome, but little evidence exists regarding whether the concept relates to lung injury in patients with healthy lungs. This study hypothesized that higher mechanical power is associated with greater postoperative respiratory failure requiring reintubation in patients undergoing general anesthesia. Methods: In this multicenter, retrospective study, 230,767 elective, noncardiac adult surgical out- and inpatients undergoing general anesthesia between 2008 and 2018 at two academic hospital networks in Boston, Massachusetts, were included. The risk-adjusted association between the median intraoperative mechanical power, calculated from median values of tidal volume (V^t), respiratory rate (RR), positive end-expiratory pressure (PEEP), plateau pressure (P^plat), and peak inspiratory pressure (P^peak), using the following formula: mechanical power (J/min) = 0.098 × RR × V^t× (PEEP + ½[P^plat- PEEP] + [P^peak- P^plat]), and postoperative respiratory failure requiring reintubation within 7 days, was assessed. Results: The median intraoperative mechanical power was 6.63 (interquartile range, 4.62 to 9.11) J/min. Postoperative respiratory failure occurred in 2,024 (0.9%) patients. The median (interquartile range) intraoperative mechanical power was higher in patients with postoperative respiratory failure than in patients without (7.67 [5.64 to 10.11] vs. 6.62 [4.62 to 9.10] J/min; P < 0.001). In adjusted analyses, a higher mechanical power was associated with greater odds of postoperative respiratory failure (adjusted odds ratio, 1.31 per 5 J/min increase; 95% CI, 1.21 to 1.42; P < 0.001). The association between mechanical power and postoperative respiratory failure was robust to additional adjustment for known drivers of ventilator-induced lung injury, including tidal volume, driving pressure, and respiratory rate, and driven by the dynamic elastic component (adjusted odds ratio, 1.35 per 5 J/min; 95% CI, 1.05 to 1.73; P = 0.02). Conclusions: Higher mechanical power during ventilation is statistically associated with a greater risk of postoperative respiratory failure requiring reintubation.