Selection criteria

Primary inclusion criteria were any observational or interventional study of adult cardiac surgery patients that presented short-term postoperative mortality or complication data and presented sub-group analysis of outcomes for ex-smokers and current smokers. Current smoking was defined as smoking at least one cigarette per day within 1 week of the date of operation, and ex-smokers were defined as patients who had ceased smoking over 1 week prior to the date of operation. The primary outcomes were defined as 30-day or in-hospital all-cause mortality and overall postoperative pulmonary complications (including pneumonia, clinically significant atelectasis, prolonged mechanical ventilation, ARDS, pneumothorax and pleural effusion requiring drainage). Secondary outcomes were defined as postoperative pneumonia (in isolation), postoperative myocardial infarction, postoperative neurological event (stroke or TIA), new postoperative renal failure or dialysis requirement, sternal wound infection (superficial or deep) and length of postoperative ICU stay. The definition of ex-smoking status for each source study was recorded.