In Reply:
We extend our heartfelt gratitude to Dr. González, Dr. Maldonado, and Dr. Cornejo for their invaluable feedback, and to Dr. Edmark and Dr. Östberg for their perceptive remarks on our study about individualized positive end-expiratory pressure (PEEP) in managing postoperative atelectasis in obese patients. We cherish their comprehensive and constructive insights and seize this opportunity to discuss and clarify their raised points.
González et al. proposed avoiding recruitment maneuvers in the fixed PEEP group to better demonstrate the effects of individualized PEEP. We emphasize that recruitment maneuvers in the fixed PEEP group are integral to the PEEP titration process, aimed to maintain process blinding and adhere to lung-protective ventilation strategies. Given the high risk of severe postanesthesia atelectasis in morbidly obese patients, we considered these maneuvers essential.
Dr. González et al. indicated the high percentage of not–well-aerated lung in our study. We argue that labeling the extent of poorly aerated lung as “high” is not precise. Research by Reinius et al. showed that, in obese patients without PEEP during anesthesia induction, poorly aerated lung reached 50%, with nonaerated and poorly aerated lung accounting for 11% and 39%, respectively, significantly higher than our study’s 9.5% and 29.9% after extubation. Thus, our results indicate that individualized PEEP markedly improves lung ventilation in obese patients.
Dr. González et al. observed that an additional 2 cm H2O might not sufficiently counter the rise in individualized PEEP caused by pneumoperitoneum. We concur with this point, as discussed in our article’s limitations section in the Discussion. However, we did not retitrate the individualized PEEP under pneumoperitoneum due to potential alveolar damage from multiple recruitment maneuvers and time constraints.
In terms of the parameter for individualized PEEP titration, we agree that under zero-flow conditions, static compliance more accurately reflects the PEEP’s impact on the respiratory system’s elastic properties. However, according to the formula: Mechanical power = 0.098 * Respiratory Rate * VT * (PEEP + 0.5δP + [Ppeak − Pplat]) peak airway pressure and its associated dynamic compliance are also important indicators for assessing the mechanical power during mechanical ventilation on the respiratory system. In obese patients, significant derecruitment of terminal bronchioles delays the redistribution of gas within the distal alveoli. Hence, we chose dynamic compliance as our parameter for individualized PEEP titration. Studies on individualized PEEP based on dynamic compliance have also demonstrated its effectiveness.
The considerable variability in individualized PEEP in our study indicates that body mass index, the only demographic or anthropometric parameter correlated to individualized PEEP, has limited influence on its determination. Therefore, predicting individualized PEEP values remains challenging, and its specific value still depends on a titration process. Moreover, the broad variability in individualized PEEP does not undermine the clinical utility of fixed PEEP. For instance, in minor surgeries, considering the time constraints of titration process, using a fixed, low-level PEEP might be more viable.
Dr. Edmark and Dr. Östberg raised concerns about the impact of ventilation strategies during the emergence period on the severity of postoperative atelectasis. We fully recognize the vital role of emergence ventilation strategies in postoperative atelectasis development. However, some minor issues arose during the trial execution and in our article. First, in line with the design of Pereira et al., we intended to extubate in pressure–support mode but erroneously used pressure–control mode. Second, we regret the lack of clarity in describing postextubation oxygenation strategies. In the Materials and Methods section, under Intervention and Control, our intended message was: “Patients in the postanesthesia care unit were not routinely given supplemental oxygen postextubation unless the Spo2 dropped less than 92%. After returning to the ward, supplemental oxygen was provided through a venturi mask at a flow rate of 3 l/min until 8 am the next day.”
It is essential to correct a misunderstanding by Dr. Edmark and Dr. Östberg about the extent of postoperative atelectasis. In our study, we calculated the actual volume of lung tissue under four different lung aeration levels using the following formula: Tissue volume = (1 − CT number/ − 1000) × total volume. Consequently, the 9.5% in the individualized PEEP group and 13.1% in the control group represent the percentage of atelectatic lung tissue relative to the total lung tissue volume (excluding air).
Dr. Edmark and Dr. Östberg inquired about the postextubation oxygenation strategy and Paco2 30 min postextubation. We apologize for not adequately describing the postextubation oxygenation strategy. As previously stated, patients in the postanesthesia care unit were not routinely given supplemental oxygen postextubation unless the Spo2 dropped less than 92%. Additionally, the Paco2 30 min postextubation was 42.7 ± 3.9 mmHg in the PEEP8 group versus 44.1 ± 4.3 mmHg in the PEEPCdyn group (P = 0.296).
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