Authors: Müller-Wirtz L M et al.
Anesthesiology, December 18, 2025, 10.1097/ALN.0000000000005906
This study evaluated whether intraoperative mechanical power delivered by the ventilator is associated with impaired postoperative oxygenation and pulmonary complications in patients undergoing orthopedic surgery. Mechanical power represents the total energy transferred from the ventilator to the respiratory system per unit time and has been proposed as a comprehensive indicator of ventilator-induced lung injury risk.
The analysis was conducted as a post hoc evaluation of data from a previously completed cluster factorial randomized trial investigating intraoperative ventilation strategies. In the original study, patients undergoing orthopedic surgery were randomized to combinations of tidal volumes (6 ml/kg vs 10 ml/kg predicted body weight) and positive end-expiratory pressure (PEEP) levels (5 cmH₂O vs 8 cmH₂O). These different ventilation strategies created varying levels of mechanical power exposure during surgery.
The investigators calculated time-weighted mechanical power normalized to predicted body weight (MP-PBW) for each patient. This normalization allowed comparison of ventilatory energy delivery relative to patient size. The primary outcomes examined were postoperative oxygenation measured by the SpO₂/FiO₂ ratio during the first hour in the post-anesthesia care unit (PACU) and later on the hospital ward. Secondary outcomes included postoperative pulmonary complications (PPCs) and length of hospital stay.
The study included 2,860 surgical procedures performed in 2,582 patients. The average patient age was 63 years, and most patients were classified as ASA III. The mean body mass index was 31 kg/m², reflecting a relatively high prevalence of obesity within the cohort.
The average mechanical power normalized to predicted body weight was 0.20 J/min/kg PBW. The average SpO₂/FiO₂ ratio during the first hour in PACU was 353, indicating generally adequate oxygenation overall.
However, statistical analysis revealed that higher mechanical power was significantly associated with worse postoperative oxygenation. For every 0.1 J/min/kg PBW increase in mechanical power, the PACU SpO₂/FiO₂ ratio decreased by approximately 11 points. A similar reduction was observed in oxygenation measurements obtained later on the hospital ward.
In addition to impaired oxygenation, higher mechanical power was associated with an increased risk of postoperative pulmonary complications. Specifically, each 0.1 J/min/kg PBW increase in mechanical power was associated with a 55% increase in the odds of developing pulmonary complications after surgery.
Interestingly, mechanical power was not associated with increased hospital length of stay.
The investigators also compared the predictive strength of mechanical power with other commonly used ventilatory parameters such as driving pressure and peak airway pressure. The analysis showed that models using driving pressure or peak pressure explained nearly the same amount of variance in postoperative oxygenation outcomes as models incorporating mechanical power.
These findings suggest that although mechanical power may serve as a comprehensive summary of ventilatory energy delivery, simpler variables such as driving pressure may provide comparable predictive information in clinical practice.
Overall, the study supports the concept that excessive ventilatory energy delivery during surgery may contribute to postoperative pulmonary impairment. It reinforces the importance of lung-protective ventilation strategies aimed at minimizing ventilatory stress during anesthesia.
What You Should Know
Mechanical power represents the total energy delivered to the lungs by the ventilator per unit time.
Higher intraoperative mechanical power was associated with worse postoperative oxygenation.
Increased mechanical power was also linked to a higher risk of postoperative pulmonary complications.
Driving pressure showed a similar predictive relationship with postoperative oxygenation as mechanical power.
These findings support ongoing efforts to minimize ventilator-induced lung stress during surgery.
Key Points
Mechanical power integrates tidal volume, airway pressures, respiratory rate, and airflow into a single measure of ventilatory energy delivery.
Higher mechanical power during orthopedic surgery was associated with lower postoperative oxygenation.
Mechanical power increases were associated with a 55% higher risk of postoperative pulmonary complications.
Mechanical power did not affect hospital length of stay.
Driving pressure had similar predictive performance for postoperative oxygenation outcomes.
Thank you to Anesthesiology for allowing us to summarize this article.