Effects of Individualized Positive End-expiratory Pressure (PEEP) on Intrinsic PEEP and Stroke Volume During One-lung Ventilation: a Single-center, Randomized Crossover Study

Intrinsic positive end-expiratory pressure (iPEEP) frequently occurs during one-lung ventilation (OLV), which is essential for lung resection. This occurrence is driven by three primary factors. First, a significant portion of patients undergoing lung surgery have concomitant chronic obstructive pulmonary disease (COPD) and thus possess a baseline intrinsic PEEP. Second, high-frequency ventilation applied to prevent carbon dioxide accumulation during OLV shortens the expiratory time, thereby generating intrinsic PEEP. Third, the use of a narrow-bore double-lumen endobronchial tube for OLV increases airway resistance, accelerating the development of intrinsic PEEP. Intrinsic PEEP causes lung hyperinflation and elevates intrathoracic pressure, which can subsequently decrease venous return and lead to abrupt hypotension. However, research remains insufficient regarding the optimal level of extrinsic PEEP for patients who develop intrinsic PEEP during OLV. While an extrinsic PEEP of around 5 cmH2O is generally applied during OLV, some guidelines recommend completely removing extrinsic PEEP (0 cmH2O) during OLV in COPD patients. Nevertheless, this recommendation lacks robust scientific evidence. Furthermore, whether the strategy of setting extrinsic PEEP at approximately 70% of intrinsic PEEP-as suggested by studies in critically ill patients-is equally valid in the intraoperative OLV environment remains unverified. Theoretically, if extrinsic PEEP exceeds intrinsic PEEP, it may exacerbate lung hyperinflation by increasing expiratory resistance. Conversely, an extrinsic PEEP that is too low may cause airway collapse during expiration, paradoxically worsening gas trapping. Therefore, this study aims to evaluate the effects of three extrinsic PEEP settings-5 cmH2O, 0 cmH2O, and an individualized PEEP (70% of the measured intrinsic PEEP)-on intrinsic PEEP and hemodynamic stability using a randomized, crossover design.