Data collection
We used a standardised case report form for data collection. Intraoperatively, we collected all ventilatory data and vital signs prospectively as the lowest and/or highest values during the procedure. The research staff collected all data directly from the clinical chart source data. Until postoperative day seven or hospital discharge (whichever came first), the trial research team assessed all patients daily. Research staff blinded to the intraoperative intervention collected information regarding the clinical outcomes. After the first 7 days (if the patient was still in hospital), we retrieved additional data from the electronic medical record.