Abstract Background Mechanical power (MP) describes the energy delivered to the respiratory system over time. The power transmitted to the lungs, particularly the resistive component, has been implicated in ventilator-induced lung injury. However, data are limited on how MP and its individual components are distributed during pneumoperitoneum (PnP) and Trendelenburg positioning, and whether the resistive component is the major contributor under these conditions. We hypothesize that the distribution of mechanical power components are distinct between the total respiratory system (MPRS) and the lung (MPL) across surgical stages, with the resistive component being the major contributor to lung mechanical power during Trendelenburg postioning. Methods This study included 35 ASA I-II adults (≥18 years) undergoing robotic surgery with pneumoperitoneum and Trendelenburg positioning. Ventilatory and respiratory mechanics data were collected at four surgical stages: (1) baseline (post-induction), (2) PnP inflation, (3) Trendelenburg/docked robot, and (4) PnP deflation. Ventilation was volume-controlled (Vt = 6-10mL/kg predicted body weight, PEEP=6-8cmH2O, FiO2=0.3-1 titrated to SpO2, and RR adjusted to EtCO2=35-45mmHg). An esophageal balloon was used to estimate pleural pressure and partition lung and chest wall components. Pressures, flow, and volume were continuously recorded for the calculation of total mechanical power and its static, dynamic, and resistive components. Results MPRS increased significantly from baseline (∼8J/min, p 0.001) through pneumoperitoneum and peaked during the Trendelenburg stage (∼17J/min, p 0.001), then decreased after deflation but remained above baseline (∼13J/min, p 0.001) (Figure A). During Trendelenburg, partitioned analysis (Figure B) showed that the dynamic and static elastic components accounted for most of the rise in MPRS (39% and 37%, respectively), with the resistive component contributing a lesser effect. MPL increased during the surgical stages from ∼5-6J/min to ∼8-9J/min (p 0.001) and interestingly remained elevated after pneumoperitoneum deflation (Figure C). In contrast to MPRS, the resistive component of MPL contributed the largest fraction (39% of total MPL), with dynamic and static elastic components contributing 31% and 30%, respectively, during Trendelenburg (Figure D). Conclusion MPRS increases substantially during pneumoperitoneum and Trendelenburg, with a disproportionate distribution pattern where the chest wall absorbs most of the energy. MPRS is driven by elastic components, reflecting the greater effort needed to maintain tidal volumes, while MPL is dominated by resistive energy, indicating altered and more stressful airflow dynamics. Both remain elevated after deflation, indicating that changes in lung mechanics were not immediately reversible and emphasizing the need for ventilation strategies that restore lung aeration and normal mechanics. This abstract is funded by: NIH R01 HL121228
Machtoub et al. (Fri,) studied this question.