Study classification within a systematic review of prone ventilation David Noble, NHS Scotland 9 March 2012 Dear Editor, I note the study of Mancebo et al has been classified by Abroag et al (Table 1) as one that used "protective lung ventilation". The study of Mancebo et al commenced in 1998 before "ARDSnet" was published. These authors state that up to 10ml/kg of (actual) body weight and up to 35 or 40cm of water for a plateau pressure was considered acceptable. The accompanying supplement to that paper indicates that even these targets were breached in over 10% of cases. Can the study of Mancebo et al really be classified as one that used "lung protective ventilation"? Competing interests None.