Mechanical ventilation mode and postoperative pulmonary complications

The results from Bagchi et al.'s study support volume control ventilation during surgery to reduce the risk of postoperative pulmonary complications (PPCs) 1. The authors used strong methodology and statistical analysis, with thorough attempts to control for confounding variables. They highlighted the importance of tailoring the mode of mechanical ventilation to the individual patient and their surgery, with appropriate positive end-expiratory pressure (PEEP) and minimisation of driving pressure. However, I would like to invite the authors to reply to several issues that their study did not address. Firstly, this study included only patients who had a tracheal tube: do the authors think that their results are generalisable to the surgical population, given that supraglottic airway devices are now the predominant airways used for general anaesthesia delivery in the UK 2? Did the authors consider any reasons for changing between modes of mechanical ventilation, for example, when managing difficult ventilation intra-operatively, which may have increased the risk of PPCs? Or the use of alternative modes of mechanical ventilation, such as pressure support ventilation or pressure control volume-guaranteed ventilation modes? The authors acknowledged the potential for unmeasured, unknown confounders in their analysis, but I think that there was a significant number of these in their study, such as: ethnicity; social deprivation; smoking history; intra-operative recruitment manoeuvres; minimally invasive surgical techniques; postoperative analgesia dosage and duration; postoperative mobilisation; peri-operative incentive spirometry; lung expansion techniques; and chest physiotherapy. Are the authors confident about their findings, despite the potential confounding influence of these? I would argue that it is not the mode of mechanical ventilation that is important 3, but rather intra-operative vigilance of the driving pressures, particularly when respiratory compliance changes frequently, and use of appropriate ventilator alarms and pressure limits. Considering the long-term detrimental consequences of PPCs 4, would the authors agree there is now sufficient equipoise for a randomised controlled trial to determine if any single mode of mechanical ventilation is superior to the others in preventing PPCs?