Chen 2013.

Methods	Single‐centre RCT
Participants	Setting: Prince of Wales Hospital, Hong Kong, China Inclusion criteria: ASA I‐IV patients, aged > 18 years, scheduled for elective open colorectal surgery Exclusion criteria: patients with ongoing infection and those with fever in the 24 h before surgery; patients with marked impairment of gaseous exchange; surgery for which primary wound closure; in the opinion of the attending anaesthesiologist that nitrous oxide administration was contraindicated Participant numbers: 93 randomly assigned; 91 analysed
Interventions	Intervention: anaesthesia was induced with propofol 1 to 2.5 mg/kg. Patients received sevoflurane targeted to achieve a bispectral index value between 40 and 60. Intraoperative analgesia was provided by remifentanil infusion 0.1 to 0.5 μg/kg/min and intravenous morphine 0.1 to 0.15 mg/kg, 30 min before completion. Muscle relaxation was facilitated by rocuronium. The lungs were ventilated through a tracheal tube using 70% nitrous oxide and 30% oxygen. Control: anaesthesia was induced with propofol 1 to 2.5 mg/kg. Patients received sevoflurane targeted to achieve a bispectral index value between 40 and 60. Intraoperative analgesia was provided by remifentanil infusion 0.1 to 0.5 μg/kg/min and intravenous morphine 0.1 to 0.15 mg/kg, 30 min before completion. Muscle relaxation was facilitated by rocuronium. The lungs were ventilated through a tracheal tube using either 30% oxygen with 70% nitrogen or 80% oxygen with 20% nitrogen.
Outcomes	Primary outcomes: Inhospital case fatality rate Secondary outcomes: Myocardial infarction: The diagnosis of myocardial infarction required any one of the following criteria: 1. A typical rise in troponin or a typical fall in an increased troponin detected at its peak after surgery in a patient without a documented alternative explanation for an increased troponin measurement (e.g. pulmonary embolism). This criterion also required that one of the following must also exist: A. Ischaemic signs or symptoms (i.e., chest, arm, neck, or jaw discomfort; shortness of breath; and pulmonary oedema); B. Development of pathologic Q waves present in any two contiguous leads that are ≥30 ms; C. ECG changes indicative of ischaemia (ST segment increase [≥2 mm in leads V1, V2, or V3; or ≥1 mm in the other leads], ST segment depression [≥1 mm], or symmetric inversion of T waves ≥1 mm) in at least two contiguous leads; D. Coronary artery intervention (i.e., percutaneous coronary intervention or coronary artery bypass graft surgery); E. New or presumed new cardiac wall motion abnormality on echocardiography or new or presumed new fixed defect on radionuclide imaging. 2. Pathologic findings of an acute or healing myocardial infarction. 3. Development of new pathologic Q waves on an ECG if troponin levels were not obtained or were obtained at times that could have missed the clinical event. Pneumonia: The definition of pneumonia required any one of the following criteria: 1. Rales or dullness to percussion on physical examinations of chest AND any of the following: A. New onset of purulent sputum or change in character of sputum; B. Isolation of organism from blood culture; C. Isolation of pathogen from specimen obtained by transtracheal aspirate, bronchial brushing, or biopsy. 2. Chest radiography showing new or progressive infitrate, consolidation, cavitation, or pleural effusion AND any of the following: A. New onset of purulent sputum or change in character of sputum; B. Isolation of organism from blood culture; C. Isolation of pathogen from specimen obtained by transtracheal aspirate, bronchial brushing, or biopsy; D. Isolation of virus or detection of viral antigen in respiratory secretions; E. Diagnostic single‐antibody titer or four‐fold increase in paired serum samples for pathogen; F. Histopathologic evidence of pneumonia. Wound infection: diagnosed by ASEPSIS > 20 Length of hospital stay
Notes	Two patients were excluded after randomization because their surgeries were cancelled
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "Patients were randomly allocated from a computer‐generated list."
Allocation concealment (selection bias)	Low risk	The random sequence was accessed through an intranet system.
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	This was not reported.
Blinding of outcome assessment (detection bias) Inhospital case fatality rate/length of stay	Low risk	The outcome measurement is not likely to be influenced by lack of blinding.
Blinding of outcome assessment (detection bias) Complications	Low risk	Quote: "The complications were examined by ward medical staff who were unaware of the allocated group identity."
Incomplete outcome data (attrition bias) All outcomes	Low risk	Missing outcome data balanced in numbers across intervention groups, with similar reasons for missing data across groups.
Selective reporting (reporting bias)	Low risk	All outcomes described in methods section reported.
Other bias	High risk	Fewer than 50 participants per arm.