 All patients undergoing cardiothoracic surgery develops some degree of postoperative pulmonary dysfunction PPD, including hypoxemia, increased work of breathing, shallow respiration and ineffective cough. Respiratory symptoms of larger clinical significance are better investigated, known as postoperative pulmonary complications PPC, including pleural effusion, atelectasis, pneumonia and ARDS. Pathophysiology is complex and multifactorial, and there is a continuum between PPD and PPC that has not yet been well explored. A large proportion of patients readmitted to CICU present respiratory failure, significantly accounting for morbidity, mortality, and costs. 