Comparison of Two Strategies of One-lung Ventilation in Patients Undergoing Carcinological Lung Resection Surgery: "Open Lung" Approach With Individualized Level of Positive End-expiratory Pressure Titrated According to the Best Lung Compliance, Versus "Standard" Care: a Randomized Controlled Trial

Pulmonary resection surgery plays a key role in the treatment of localized lung cancer. During thoracic surgery, lung isolation is necessary. One-lung ventilation (OLV) is associated with frequent intraoperative respiratory complications, hypoxemia or lung injury related to mechanical ventilation. Intraoperative events increase the risk of postoperative complications resulting from either hypoxemia (atrial fibrillation, delirium, acute kidney injury) or lung injury (atelectasis, pulmonary edema, pneumonia, acute respiratory distress syndrome (ARDS)).

During OLV, a protective ventilation strategy is now recommended, including a low tidal volume (VT), using the lowest fraction of inspired oxygen (FiO2) due to the toxicity of high-oxygen concentration, and recruitment maneuvers (RM). But there is no consensus on the level of positive end-tidal pressure (PEEP) to apply. A low level of PEEP increases the risk of alveolar collapse, when a too high level leads to alveolar overdistension and increases lung dead space. The PEEP is usually arbitrary fixed to 5 cmH2O for every patient, which does not take into account the individual characteristics of the patient. Recent clinical trials in thoracic surgery showed that titration of PEEP according to the lowest airway driving pressure [end-inspiratory plateau pressure - total end-expiratory pressure], compared to a standard PEEP of 5 cmH2O, increased oxygenation and lung mechanics, and decreased significantly respiratory complications.

The transpulmonary pressure (PTP) is the instantaneous difference between alveolar pressure and pleural pressure. In order to optimize the alveolocapillary gas exchange, the level of PEEP should be titrated until achieving the best lung compliance (CL), defined by the ratio [(tidal volume) / (driving PTP = end-inspiratory PTP - end-expiratory PTP)]. As the tidal volume is set on the ventilator, the level of PEEP corresponding to the best CL is the one associated with the lowest driving PTP. The "open lung" strategy consists in setting the level of PEEP according to the best CL, which is an individualized approach, probably more physiologic than the standard care.

The esophageal pressure (PES) measured by an esophageal catheter is a validated estimation of the pleural pressure. Then, the PTP could be approximated by the difference [airway plateau pressure - PES]. The placement of an esophageal catheter is safe provided that the use respects contraindications (mainly esophageal disease or varices).

In ARDS, the open lung approach using an esophageal catheter was associated with a better clinical outcome than the standard non-individualized protocol. In laparoscopic surgery, the effects of PEEP on the PTP is also well described. In thoracic surgery, to date, monitoring PES and PTP is not part of the usual care. To our knowledge, only one study described the PTP changes during OLV. In this study, the best PEEP during OLV differed from one patient to another, which goes against the "one size fits all" theory. Thus, the PEEP should be titrated and individualized. Nevertheless, the airway driving pressure is only an approximation of the PTP, since it does not take into account the pleural pressure, which is a non-negligible extra-alveolar factor when talking about patients with lung or pleural diseases. Measuring the driving PTP using an esophageal catheter is certainly more accurate.