Patient No. refers to the order of enrolment to the study. Patients were mechanically ventilated at volume assist-control mode; inspiratory flow ranged within 0.6–0.9 L·s⁻¹; respiratory rate (range 19–28·min⁻¹) was adjusted to maintain an arterial pH of ≥7.30. For males, predicted body weight was calculated as  = 50+(Height (cm)–152.4)×0.91; for females, 50 was replaced by 45.5. Patients weaned from mechanical ventilation and discharged from the intensive care unit (ICU) were considered as survivors. BMI: body mass index; SAPS II: simplified acute physiology score II; P_a,O2: arterial oxygen tension; F_I,O2: inspiratory oxygen fraction; P_a,CO2: carbon dioxide arterial tension; PEEPe: externally applied positive end-expiratory pressure; V_T: tidal volume; PBW: predicted body weight; P_2,aw: plateau tracheal pressure; M: male; S: survival; F: female; D: death (in the ICU). ^#: on ICU admission; ^¶: variables recorded just prior to study enrolment, whilst there was no patient-ventilator asynchrony in any case; ⁺: microorganism isolated in tracheobronchial aspirates (positive cut-off value = 10⁵ colony forming units·mL⁻¹); ^§: diagnosis established by PCR for Legionella and detection of Legionella antigen in urine.