Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited. Positive end-expiratory pressure Luciano Gattinoni a,b , Eleonora Carlesso b , Luca Brazzi a,b and Pietro Caironi a,b Introduction It is a common notion that mechanical ventilation may induce per se a lung injury when leading to unphysiolo- gical stress and strain of the lung parenchyma, resulting in inflammatory responses and mechanical lesions up to stress at rupture. Therefore, it is widely accepted that limiting tidal volume to 6 ml/kg ideal body weight (IBW) and/or plateau airway pressure below 30 cmH 2 O may prevent or limit possible injury of mechanical ventilation in patients affected by acute lung injury (ALI) [1]. Low tidal volume and limited plateau pressure, however, are a part of a more integrated ventilator strategy known as ‘lung protective strategy’ [2]. This is based on two basic concepts: limiting global stress and strain (plateau pres- sure and tidal volume), and preventing intratidal collapse of pulmonary units by providing an end-expiratory pres- sure (positive end-expiratory pressure, PEEP) sufficient to keep the lung open throughout the respiratory cycle. Whereas the first part of the protective lung strategy has been tested and proved effective in a randomized trial [1], the second part related to the PEEP selection has not been proved and is still a subject of debate. In this area, we deal with two kinds of approaches that are sometimes difficult to integrate. The first one tests a given clinical strategy as ‘lower’ versus ‘higher’ PEEP on an epidemio- logical basis, typically in large outcome studies. The second one aims to understand the mechanism through which a given maneuver (such as PEEP selection or recruitment maneuver) is operating, and on which basis it should provide benefit, thereby individualizing the PEEP level to be applied. In this brief review, we will try to integrate these two approaches when discussing the most recent studies that appeared in the literature dealing with PEEP selection and recruitment maneuver in acute respiratory distress syndrome (ARDS). a Dipartimento di Anestesia, Rianimazione (Intensiva e Subintensiva) e Terapia del Dolore, Fondazione IRCCS – ‘Ospedale Maggiore Policlinico Mangiagalli Regina Elena’ di Milano and b Dipartimento di Anestesiologia, Terapia Intensiva e Scienze Dermatologiche, Universita ` degli Studi, Milan, Italy Correspondence to Professor Luciano Gattinoni, MD, FRCP, Dipartimento di Anestesiologia, Terapia Intensiva e Scienze Dermatologiche, Fondazione IRCCS – ‘Ospedale Maggiore Policlinico, Mangiagalli, Regina Elena’ di Milano, Via Francesco Sforza 35, 20122 Milan, Italy Tel: +39 02 55033232; fax: +39 02 55033230; e-mail: gattinon@policlinico.mi.it Current Opinion in Critical Care 2010, 16:39–44 Purpose of review In the last 2 years, several reports have dealt with recruitment/positive end-expiratory pressure (PEEP) selection. Most of them confirm previous results and few add new information. Recent findings It has been definitely confirmed that opening pressures are different throughout the acute respiratory distress syndrome lung parenchyma, ranging from 5–10 up to 30–40cmH 2 O. The highest opening pressures are required to open the most dependent lung regions. It has been found that in 2 s, most of the recruitable lung regions may be open when a proper pressure is applied. The best way to assess recruitment is computed tomography scanning, whereas lung mechanics are a reasonable bedside surrogate. Impedance tomography has been increasingly tested, whereas gas exchange is the less reliable indicator of recruitment. A large outcome study showed that higher PEEP might provide survival benefit in a subgroup of more severe patients as compared with lower PEEP. To set PEEP in each individual patient, the use of the expiratory limb of the pressure–volume curve has been suggested. Setting PEEP according to transpulmonary pressure has a robust physiological background, although it requires confirmatory study. Summary Indiscriminate application of recruitment maneuver in unselected acute respiratory distress syndrome population does not provide benefits. However, in the most severe patients, recruitment maneuver has to be considered and higher PEEP applied. To individualize PEEP, the expiratory phase has to be considered, and the esophageal pressure measurement to compute the transpulmonary pressure should be progressively introduced in clinical practice. Keywords computed tomography scanning, esophageal pressure, lung recruitment, positive end- expiratory pressure, pressure–volume curve Curr Opin Crit Care 16:39–44 ß 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins 1070-5295 1070-5295 ß 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins DOI:10.1097/MCC.0b013e3283354723