Lung-Protective Ventilation in ARDS

Throughout the 1990s, mounting evidence from animal models and small clinical studies suggested that conventional tidal volumes of 10-15 mL/kg were amplifying lung injury in ARDS patients through a mechanism termed ventilator-induced lung injury (VILI). Amato and colleagues published a landmark single-centre trial in 1998 demonstrating that a protective strategy using 6 mL/kg tidal volumes with higher PEEP dramatically reduced 28-day mortality compared to conventional ventilation. While criticized for its small size and differences in PEEP between groups, this trial provided the clearest signal that how we ventilate matters as much as why we ventilate, and set the stage for the definitive ARDS Network trial.

The ARDS Network ARMA trial (2000) is one of the most important critical care trials ever conducted. In 861 patients with ARDS, ventilation with 6 mL/kg predicted body weight reduced mortality by 22% relative to 12 mL/kg (31.0% vs 39.8%). The trial was stopped early for efficacy — a rarity in critical care. This was not a subtle signal requiring meta-analysis; the mortality reduction was immediate, consistent, and biologically plausible through reduced VILI. Low tidal volume ventilation became the single most impactful intervention in ARDS management and remains the cornerstone of lung-protective ventilation two decades later.

With low tidal volumes established, the next frontier was optimising PEEP. Three large RCTs — ALVEOLI (2004), LOV (2008), and ExPress (2008) — compared higher versus lower PEEP strategies in ARDS. None individually showed a mortality benefit, though an individual patient data meta-analysis suggested benefit in moderate-severe ARDS (P/F <200). In 2015, Amato's group introduced the concept of driving pressure (plateau pressure minus PEEP) as a superior predictor of outcome, using individual patient data from nine RCTs to show that driving pressure was the ventilatory variable most strongly associated with survival. The ART trial (2017) tested an aggressive open-lung approach with recruitment manoeuvres and titrated PEEP, but found increased mortality — a cautionary tale that more aggressive strategies can cause harm. These extension studies refined our understanding: the key is not just low volumes but low mechanical stress, measured by driving pressure.

Major international guidelines universally recommend low tidal volume ventilation (6 mL/kg predicted body weight) for all ARDS patients. The ATS/ESICM/SCCM 2017 clinical practice guideline provides a strong recommendation for low tidal volumes and a conditional recommendation for higher PEEP in moderate-severe ARDS. The Surviving Sepsis Campaign 2021 guidelines reinforce low tidal volume ventilation for sepsis-associated ARDS. Guidelines also recommend targeting plateau pressures below 30 cmH2O, and increasingly reference driving pressure as a useful clinical target, though no RCT has yet tested a driving-pressure-guided strategy.

Low tidal volume ventilation at 6 mL/kg predicted body weight remains the undisputed standard of care for ARDS, yet implementation gaps persist — studies consistently show that a significant proportion of patients still receive tidal volumes above target. The field has moved toward a more nuanced understanding of mechanical power and driving pressure as integrative measures of ventilator-induced lung injury. Personalised PEEP titration strategies — using electrical impedance tomography, oesophageal pressure monitoring, or driving pressure optimisation — are under active investigation. The concept of 'ergotrauma' (total energy delivered to the lung) is emerging as a unifying framework. Current frontiers include ultra-protective ventilation with extracorporeal CO2 removal, the role of spontaneous breathing in ARDS, and whether driving-pressure-guided strategies can further improve outcomes beyond the gains achieved by ARMA.