The preventive role of higher PEEP in treating severely hypoxemic ARDS

This review summarizes knowledge and evidence on the use of positive end-expiratory pressure (PEEP) in patients with severely hypoxemic acute respiratory distress syndrome (ARDS). More specifically, it documents the current evidence on the effects of higher PEEP in preventing (or attenuating) lung damage during the ventilatory management of patients with severely hypoxemic ARDS. No established threshold has been set to define severely hypoxemic ARDS and higher PEEP. In this review, those variables are defined as PaO(2)/F(I)O(2) ≤100 mm Hg and ≥15 cm H(2)O, respectively. In ARDS, the intensity of hypoxemia correlated with the amount of lung recruitability. In ARDS, the primary objective of PEEP is to increase the amount of non-aerated lung at the end of expiration. In early ARDS with a diffuse pattern and severe hypoxemia, higher PEEP contributes to lung recruitment by maintaining lung recruitment elicited by tidal breath and recruitment maneuvers as well as minimizes the repeated opening and closure with no significant overdistension. Three clinical trials comparing high PEEP + low tidal volume to low PEEP + large tidal volume found benefits favoring the former combination. Three large multicenter randomized controlled trials did not demonstrate a significant effect on patient outcome of higher or lower PEEP at a fixed low tidal volume. The meta-analysis on individual data of these three studies showed that the hospital mortality was not significantly different between the two groups of patients, was significantly lower in the higher PEEP group in the subset of ARDS patients (PaO(2)/F(I)O(2) ≤200 mm Hg), and tended to be higher in the higher PEEP group in the subset of patients with acute lung injury (200< PaO(2)/F(I)O(2) ≤300 mm Hg). Therefore, higher PEEP should be used in patients with the highest lung recruitability and in the most hypoxemic patients. Higher PEEP should be used with caution in patients less severe hypoxemic (acute lung injury).To deliver optimal PEEP to those ARDS patients with the highest lung recruitability, this technique should be monitored at the bedside. Alternative methods are under investigation as part of a decremental PEEP trial.