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

Abstract

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 (Vt), respiratory rate (RR), positive end-expiratory pressure (PEEP), plateau pressure (Pplat), and peak inspiratory pressure (Ppeak), using the following formula: mechanical power (J/min) = 0.098 × RR × Vt × (PEEP + ½[Pplat – PEEP] + [Ppeak − Pplat]), 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. Editor’s Perspective What We Already Know about This Topic What This Article Tells Us That Is New

Mechanical Power: Correlate or Cause of Ventilator-induced Lung Injury?

“…Santer et al 5 convincingly confirm their primary hypothesis that mechanical power is associated with lung injury. Associations can be valuable because they help clinicians anticipate events, but it is also worth considering that the difference in primary outcome between the lowest and highest quintiles was 1.1 minus 0.7% = 0.4%, which corresponds to a number needed to treat of 250 even assuming that patients can be moved across so many quintiles, which seems unlikely since power is probably mostly determined by individual patient need.…”

“…Santer et al . 5 used an equation developed 2021 for epidemiologic studies, 7 which includes three basic terms. One term expresses a “static” component—that is, the contribution of positive end-expiratory pressure (PEEP) or stored energy.…”

“…In this issue of Anesthesiology, Santer et al contribute a retrospective analysis of 230,767 adults who had elective noncardiac surgery with general anesthesia between 2008 and 2018 in two academic hospitals. 5 The authors found that both higher mechanical power and temporal increases of mechanical power during anesthesia were associated with postoperative respiratory failure requiring intubation. These findings advance our understanding of ventilator-induced lung injury, and are generally consistent with critical care studies suggesting that mechanical power is associated with adverse outcomes, including death.…”

Comparisons of Mechanical Power and Respiratory Mechanics in Pressure-Controlled Ventilation and Volume-Controlled Ventilation during Laparoscopic Cholecystectomy in Elderly Patients

“…In a previous clinical study of patients who underwent major non-cardiothoracic and non-intracranial surgeries, a higher MP was associated with a higher risk of postoperative pulmonary complications, including acute respiratory failure [ 4 ]. Another retrospective analysis of 230,767 non-cardiac surgical cases also showed similar results [ 5 ]. In their study, intraoperative value of MP (median [interquatile range, IQR]) was significantly higher in patients who required reintubation due to postoperative respiratory failure within 7 days after surgery than in patient who did not (7.67 [5.64–10.11] J/min vs. 6.62 [4.62–9.10] J/min) [ 5 ].…”

“…In their study, intraoperative value of MP (median [interquatile range, IQR]) was significantly higher in patients who required reintubation due to postoperative respiratory failure within 7 days after surgery than in patient who did not (7.67 [5.64–10.11] J/min vs. 6.62 [4.62–9.10] J/min) [ 5 ]. In addition, when performed adjusted analysis for known factors inducing VILI such as Vt, driving pressure (DP), and RR, MP remained an independent risk factor for postoperative respiratory failure [ 5 ].…”