Driving pressure vs. oxygenation-based PEEP titration strategies in ARDS patients: a physiological study

The aim of this study was to evaluate the effects of three different PEEP titration strategies in ARDS patients, one based on driving pressure and two based on oxygenation (one PEEP level according to the high PEEP/FiO₂ table and a two fixed PEEP levels, i.e., 5 and 15 cmH₂O, according to the modified Berlin definition severity), on gas exchange, partitioned respiratory mechanics and mechanical power during protective lung ventilation.

Prospective observational study including 35 sedated, paralysed and mechanically ventilated patients with ARDS according to the Berlin definition within 48 h from admission to a medical-surgical ICU. Each patient underwent PEEP titration according to a clinical (based on driving pressure), empirical (based on high PEEP/FiO₂ table) and fixed (5 or 15 cmH₂O for patients with PaO₂/FiO₂ less than or greater than 150 mmHg) strategy. After 20 min of each phase, partitioned respiratory mechanics, gas exchange and hemodynamics were measured.

In the whole population, when comparing empirical versus clinical PEEP (15 [10-18] vs. 10 [8-10] cmH₂O), end-inspiratory airway pressure, lung and respiratory system elastances, mechanical power, lung stress and PaCO₂ were significantly higher, but PaO₂/FiO₂ was higher with empirical PEEP. In mild-moderate ARDS patients, end-inspiratory airway pressure and lung stress were significantly higher with clinical (8 [8-10] cmH₂O) and empirical PEEP (10 [8-12] cmH₂O) as compared to fixed PEEP (5 cmH₂O); mechanical power was higher with empirical PEEP as compared to other PEEP titration strategies. Gas exchange did not differ. In moderate-severe ARDS patients, end-inspiratory airway pressure, lung stress, mechanical power, PaO₂/FiO₂ and PaCO₂ were significantly higher with fixed (15 cmH₂O) and empirical PEEP (17 [14-18] cmH₂O) as compared with clinical PEEP (10 [8-10] cmH₂O).

Clinical PEEP titration provided better respiratory mechanics in terms of lower end-inspiratory airway pressure, lung stress and elastance and lower PaCO₂ compared with a high PEEP/FiO₂ table. In mild-moderate ARDS patients, a fixed PEEP level (5 cmH₂O) provided lower end-inspiratory airway pressure and lung stress without detrimental effects on gas exchange compared to empirical or clinical PEEP. In moderate-severe ARDS patients, empirical and fixed PEEP (15 cmH₂O) levels resulted in higher levels of end-inspiratory airway pressure, lung stress, PaO₂/FiO₂ and PaCO₂ compared to more moderate PEEP levels.