Ayse SENCAN, Nurseda DUNDAR, Bedirhan GUNEL, Ahmet YUKSEK
Medeniyet Medical Journal - 2026;41(2):232-233
Dear Editor, We sincerely thank the authors of the letter for their interest in our article entitled "The Effect of Flow-Controlled Ventilation on Mechanical Power During Laparoscopic Surgery: A Comparative Analysis with PCV-VG and VCV" and for their constructive and thoughtful comments. We acknowledge the observed differences in age and American Society of Anesthesiologists (ASA) physical status distributions among the ventilation groups, particularly the higher proportion of ASA-III patients in the pressure-controlled ventilation-volume guaranteed (PCV-VG) group. As our study was retrospective in design, randomization was not feasible, and group allocation reflected routine clinical practice. Intraoperative ventilatory management, including tidal volume targets, positive end-expiratory pressure administration, and pneumoperitoneum pressure, was protocolized across all groups. The mechanical power (MP) calculated in our study was derived primarily from ventilator parameters and airway pressures rather than directly from ASA classification. Although baseline cardiopulmonary reserve may influence respiratory mechanics to some extent, our analysis revealed that the primary determinants of MP were ventilator settings and mode-specific pressure-flow characteristics. Despite the higher ASA classification in the PCV group, a more favourable MP profile suggests that our findings would likely not differ in cohorts with comparable ASA distributions and might even become more pronounced under balanced baseline conditions. While we agree that the interaction between ASA status and MP remains unclear, we cannot entirely rule out residual confounding. During pneumoperitoneum, median MP values converged to approximately 8.6-9.4 J/min across ventilation modes, remaining below the frequently cited experimental threshold of 12 J/min reported in the literature. This threshold value is primarily derived from long-term ventilation models and experimental conditions, we would like to emphasise that its validity for short-term intraoperative exposure is unclear. Our primary focus was on the acute changes in lung mechanics occurring during laparoscopy and associated with pneumoperitoneum. Consequently, our analysis compares instantaneous MP across different ventilation modes during pneumoperitoneum. We believe that cumulative MP or time-weighted energy load calculations are more meaningful, especially for patients undergoing prolonged ventilation or monitored in intensive care. The clinical contribution and threshold values of the cumulative perioperative energy load during the intraoperative period are not yet clearly defined, particularly for elective surgical patients with healthy lungs who are exposed to relatively short periods of ventilation. Furthermore, long-term monitoring and analysis of measurements may be impractical during the perioperative period. Rather than evaluating long-term energy exposure, our aim was to compare the simultaneous energy transfer profiles of ventilation modes in the dynamic physiological environment created by pneumoperitoneum. Pneumoperitoneum significantly alters the elasticity of the chest wall and the mechanics of the respiratory system in laparoscopic surgery. One criticism we agree on is that, even if absolute values remain within a "safe" range in this dynamic physiological environment, relative MP changes may still reflect differences in energy transfer and stress distribution. That analyses of cumulative mechanical force during surgery have not yet been sufficiently elucidated holds significant potential for future research. Previous studies have shown that the use of mathematical formulas to calculate MP is highly consistent with actual calculations. However, the mathematical calculations have not been sufficiently or specifically tested for flow-controlled ventilation (FCV), nor have they been compared with area calculations. While this is a limitation of our study, our work may still contribute to the existing literature. The equations we used are based on approximate clinical calculation methods that are commonly found in the literature. Because the waveform characteristics of the volume-controlled ventilation, PCV-VG, and FCV modes differ, representing all modes equally with a single algebraic expression would not be physiologically appropriate. Although a combined method based on pressure-volume curve integration or bench-based cross-calibration is valuable for physiological validation, it cannot be applied to retrospective clinical datasets. Therefore, our approach favours a methodology consistent with and comparable to the clinical MP literature. We believe that our study will contribute to future research by providing evidence to support physiological comparisons of ventilation modes in laparoscopic surgery, an area in which evidence is currently limited. We agree that prospective studies integrating standardised MP calculations with postoperative pulmonary outcomes and risk-adjusted cohorts would provide a clearer indication of whether FCV or PCV-VG offers clinically meaningful protection to patients undergoing laparoscopic surgery.
