Squadrone 2005.

Methods	Randomization procedure: concealed randomization was conducted centrally through a dedicated web site using a computer‐generated block randomization schedule Allocation: not reported Blinding: allocation to treatment with oxygen or oxygen plus CPAP was not blinded. To minimize potential bias in the assessment of some of the study end points, we used measures such as objective criteria for endotracheal intubation and standardization of all co‐interventions that could have influenced outcome variables such as anaesthesia, postoperative pain control, and respiratory physiotherapy Design: randomized, controlled, unblinded study with concealed allocation Duration: June 2002 to November 2003 Multicentre: participants recruited from the 15 ICUs of the Piedmont Intensive Care Units Network in Italy Analysis (ITT): all analyses conducted on an ITT basis Informed consent: ethics committees approved the protocol and written informed consent was obtained from the participants
Participants	Number of participants: 209 Setting: 15 ICU Age (mean ± SD): O: 65; CPAP + O: 66 Gender (M/W): O: 64/40; CPAP: 71/34 Diagnostic criteria: participants scheduled for elective abdominal surgery and general anaesthesia were eligible to participate in the study if they met the following criteria: abdominal surgery requiring laparotomy and time of viscera exposure > 90 minutes. At the end of the surgical procedure, participants were extubated and underwent a 1‐hour screening test breathing oxygen through a Venturi mask at an inspiratory fraction of 0.3. Participants were included in the study if they developed a PaO2/FiO2 ratio of ≤ 300 Exclusion criteria: participants were excluded if before surgery they were > 80 or < 18 years; had a New York Heart Association functional class of II, III, or IV; had valvular heart disease, history of dilated cardiomyopathy, implanted cardiac pace maker, unstable angina, or myocardial infarction and cardiac surgery within the previous 3 months; had a history of chronic obstructive pulmonary disease, asthma, or sleep disorders; had preoperative infection, sepsis, or both; had a body mass index > 40; had a presence of tracheostomy, facial, neck, or chest wall abnormalities; required an emergency procedure (operation that must be performed as soon as possible and no longer than 12 hours after admission); or had undergone abdominal aortic aneurysm surgery, chemotherapy, or immunosuppressive therapy within the previous 3 months. Participants were also excluded if before randomization they had arterial pH < 7.3 with a PaCO2 > 50 mm Hg; arterial oxygen saturation < 80% with the maximal fraction of inspiratory oxygen; clinical signs of acute myocardial infarction; systolic arterial pressure < 90 mm Hg under optimal fluid therapy; presence of criteria for acute respiratory distress syndrome; haemoglobin < 7 g/dL, serum albumin < 3 g/dL; creatinine > 3.5 mg/dL (309 μmol/L); or a Glasgow Coma Scale < 12 Number excluded: O: 2; CPAP: 4
Interventions	Control: treated for 6 hours with oxygen through a Venturi mask at an FiO2 of 0.5 Intervention: treated with oxygen at an FiO2 of 0.5 plus a CPAP of 7.5 cm H2O Number of participants per group: O: 104;CPAP: 105 Mask: helmet
Outcomes	Primary outcome: endotracheal intubation within the first 7 days after surgery Secondary outcome: ICU and hospital length of stay; incidence of pneumonia, infection, and sepsis within the first month after surgery; hospital mortality. Pneumonia, infection, and sepsis were identified using standard definitions Mortality: O: 3CPAP: 0 Tracheal intubation rate: O: 10; CPAP: 1 ICU length of stay: O: 2.6; CPAP: 1.4 Hospital length of stay: O: 17; CPAP: 15 Treatment failure: O: 2 CPAP: 4 Adverse effects: not reported Participant compliance: O: 30 CPAP: 7 Drop‐outs/withdrawals: O: 2; CPAP: 4
Notes	Declarations of interest: none reported Funding sources for the study: none reported
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	The participants were randomly allocated
Allocation concealment (selection bias)	Low risk	Concealed randomization was conducted centrally through a dedicated web site using a computer‐generated block randomization schedule
Blinding of participants and personnel (performance bias) All outcomes	High risk	Blinding was not possible. Allocation to treatment with oxygen or oxygen plus CPAP was not blinded. To minimize potential bias in the assessment of some of the study end points, the study author used measures such as objective criteria for endotracheal intubation and standardization of all co‐interventions that could have influenced outcome variables such as anaesthesia, postoperative pain control, and respiratory physiotherapy. We contacted the authors of this study to ask about blinding of study participants and personnel but did not obtain an answer from them
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Blinding of outcome assessors was not reported. The authors only stated that the people responsible for the interventions were not involved in the study. We contacted the authors of this study to ask about blinding of study outcome assessors but did not obtain an answer
Incomplete outcome data (attrition bias) All outcomes	Low risk	No missing outcome data
Selective reporting (reporting bias)	Low risk	The study protocol was available and all of the study's pre‐specified (primary and secondary) outcomes that are of interest in the review were reported in the pre‐specified way
Other bias	Low risk	This study was not a cluster randomized trial or a cross‐over trial. This study was a randomized controlled trial. The participants were randomized. The distribution of the participants was balanced between the control and intervention groups. The authors did not deviate from the study protocol

CPAP: continuous positive airway pressure; FiO₂: fraction of inspired oxygen; ICU: intensive care unit; ITT: Intention‐to‐treat; M: men; min: minute; NPPV: noninvasive positive pressure ventilation; O: oxygen; PaCO₂: partial pressure of carbon dioxide; PaO₂: partial pressure of oxygen; PEEP: positive end‐expiratory pressure; pH: hydrogen potential; PSV: pressure support ventilation; SD: standard deviation; V_T: tidal volume; W: women.