Study	Reason for exclusion
Amato 1995	The 28 participants in this study were included in the large study published in 1998.
Badet 2009	This study assessed the role of three ventilation strategies with recruitment manoeuvres and optimal PEEP (PEEP set to 24 cm H2O and then lowered stepwise to step above which PaO2 decreased by ≥ 20%) in a random order in 12 participants with ALI or ARDS. Arterial blood gas values and static compliance were recorded at the end of each strategy. No control group, thus not an RCT.
Burns 2001	14 participants with ARDS were treated with each of ten tidal volume‐PEEP combinations, applied in random order, to assess changes in oxygenation and respiratory compliance. No control group, thus not an RCT.
Carvalho 1997	This study was a descriptive analysis of another published study (Amato 1995) and included two groups of participants with different levels of PEEP, in which physiological variables were studied.
Dellamonica 2011	In 30 participants with ALI, two levels of PEEP were applied in a random sequence to provide a simple and accurate bedside method for assessing alveolar recruitment while monitoring strain on the lungs. We had no control group, so the trial was not an RCT.
Grasso 2005	In 19 participants with ARDS divided into two groups and with different levels of PEEP, changes in oxygenation, static lung elastance and the shape of the volume‐pressure curve were assessed. Excluded because the outcomes are physiological.
Grasso 2007	In 15 participants with ARDS, two ventilatory strategies with different levels of PEEP were applied in random order. Physiological parameters and plasma inflammatory mediators were measured. No control group, thus not an RCT.
Kallet 2007	This was a review of the different ways of applying PEEP in participants with ARDS.
Oczenski 2004	This was a randomized controlled study of participants with early extrapulmonary ARDS. In this study, two groups were assigned, but both had equal levels of PEEP and differed only in the inclusion of a recruitment manoeuvre.
Ranieri 1999	This was a randomized controlled trial of participants with ARDS. Two groups were assigned with different VT and levels of PEEP. Excluded because the primary outcome is physiological (pulmonary and systemic concentrations of inflammatory mediators) and mortality is reported as a post hoc analysis.
Richard 2003	In this prospective cross‐over study, 15 participants with ALI were treated with three ventilatory strategies combining different levels of PEEP and VT to investigate changes in alveolar recruitment and oxygenation. No control group, thus not an RCT.
Toth 2007	This was a study in which 18 participants with ARDS underwent recruitment manoeuvres and decremental PEEP to reach optimal PEEP (PEEP set to 26 cm H2O and then lowered stepwise to step above which PaO2 decreased by > 10%) for assessment of respiratory and haemodynamic changes. No control group, thus not an RCT.