The definition of postoperative pulmonary complication in these earlier studies is yet to be validated,and in some includes 'physician diagnosis' as a definition of postoperative pulmonary complications.
For these reasons our definition included only those criteria that could be assessed objectively. Chest X-ray findings were reported by a radiographer who was blinded to allocation,study aims and objectives. Chest X-ray were ordered by the medical staff only if patients had adverse respiratory signs or symptoms.