Background: Intraoperative lung-protective ventilation entered practice as a bundle of low tidal volume, positive end-expiratory pressure and recruitment manoeuvres, tested and adopted together. Trials isolating the individual components have been largely null, while driving pressure has emerged as a candidate mediating variable. The field illustrates a general problem — how to interpret a bundle whose parts have not been separately established — with direct consequences for setting the ventilator.

Methods: We conducted a structured narrative review, organised chronologically, of randomised trials and meta-analyses of intraoperative ventilation in adult surgical patients. For each landmark study we recorded what was believed before it, what it tested, and what it left standing, then appraised the mediation hypothesis.

Results: An initial trial of the full bundle reduced postoperative pulmonary complications. Trials isolating higher positive end-expiratory pressure with recruitment against lower pressure, at matched tidal volume, found no benefit in open abdominal surgery or in obesity, and signalled haemodynamic compromise and over-distension. A trial of low against conventional tidal volume alone also found no difference. An individual-patient-data meta-analysis found that driving pressure — tidal volume normalised to respiratory system compliance rather than predicted body weight — tracked complications better than either component. Later syntheses associate low tidal volume with driving-pressure-guided positive end-expiratory pressure with fewer complications.

Conclusion: The evidence is best read as identifying a mediator rather than as refuting the bundle. Tidal volume and positive end-expiratory pressure appear to matter to the extent that they alter driving pressure, which is measurable at the bedside and responds to the individual patient's mechanics. We propose setting tidal volume conservatively, treating driving pressure as the titration target, and diagnosing the reason a driving pressure is high before raising positive end-expiratory pressure.