One‐lung ventilation and positive end‐expiratory pressure titration

We do not think that the negative result reported in the trial by Wang et al. rules out individualised positive end-expiratory pressure (PEEP) during one-lung ventilation [1]. It may instead reflect the limitation of setting PEEP once in a situation where lung mechanics keep changing. During one-lung ventilation, lung mechanics are unstable. Chest opening, lung manipulation, mediastinal shift, secretions, fluid administration and lung resection all change compliance and airway pressures. A PEEP level chosen at one time-point may not be optimal later in the case. This matters even more when one-lung ventilation is managed with an inspired oxygen fraction of 1.0. A high concentration of inspired oxygen can promote absorption atelectasis which may develop as surgery proceeds. A single PEEP level set before surgical incision cannot adjust to a lung that changes throughout the case. How electrical impedance tomography was used in this trial is therefore important. Wang et al. performed titration before surgery and then applied that PEEP during intra-operative one-lung ventilation. The belt was used for titration and then removed so that it was not present during surgery. In practice, electrical impedance tomography functioned here as a pre-incision PEEP calculator, not as a monitor that could support repeated reassessment during one-lung ventilation. The question is not whether to individualise PEEP, but what signal should guide it and when reassessment is needed. In thoracic surgery, this is a practical limitation because the belt lies close to the surgical field. Bedside respiratory mechanics offer something different. Driving pressure and compliance are already available from the anaesthesia workstation. They can be checked repeatedly during the case, with no extra device. Their main value is not that they give a better first estimate of the ‘best’ PEEP; their value is that they show when the lung has changed. If compliance falls or driving pressure rises during constant tidal volume ventilation, the clinician knows the current setting may no longer fit the lung. That is often the point when recruitment and repeat PEEP titration should be considered. This reading fits the wider one-lung ventilation literature. In a meta-analysis, compliance-guided individualised PEEP was associated with fewer postoperative pulmonary complications than fixed PEEP, especially when titration used dynamic compliance or a stepwise decremental method [2]. In the iPROVE-OLV trial, compliance was checked every 40 min [3]. Repeated recruitment and titration were performed when compliance fell >20% and nearly half of patients needed more than one recruitment manoeuvre during surgery. Taken together, we argue it is not enough to select an initial PEEP during one-lung ventilation and reassessment must continue throughout the case. Wang et al. have shown an important limit of intermittent implementation, not the failure of individualised PEEP itself. For routine thoracic anaesthesia, the more useful question may be simple: when lung mechanics change during one-lung ventilation, what can the anaesthetist measure immediately and act on at the bedside? On that basis, global mechanics, especially compliance and driving pressure, remain practical targets. They do not require extra hardware. They allow the clinician to recognise derecruitment, recruit again when needed and titrate PEEP during the case, rather than rely on a single pre-operative setting.