The combination of surgery and anesthesia can be associated with a number of serious complications that may impair patient recovery. In particular, postoperative pulmonary complications (PPCs), including respiratory complications such as atelectasis, pneumonia, and reintubation, are the leading cause of prolonged hospital stay, morbidity, and mortality in surgical patients [1]. PPCs are common, serious, and expensive. Health-care costs associated with the treatment of PPCs are 50 % greater than costs for treating postoperative cardiac complications. The incidence of PPCs varies depending on the clinical treatment setting, the kind of surgery studied, and the definition of PPC used. For all these reasons, incidence rates vary from 2 to 40 % [2, 3]. The actual incidence of important PPCs seems to be 2–5 % in patients undergoing thoracic or upper-abdominal surgery.

In a general sense, a PPC is any event that occurs in the postoperative period that produces physiologic dysfunction or clinical disease. A PPC may be diagnosed based on symptoms (cough, fever, abnormal breath sounds), laboratory values (hypoxemia, leukocytosis), or radiographic criteria (atelectasis or infiltrate). As a result, a PPC can be defined as simply atelectasis on a chest radiograph or as respiratory failure necessitating intubation and mechanical ventilation [2]. Brooks-Brunn [4] suggested a more specific definition that includes at least two of the following findings documented at any time during the first 6 days following surgery: new cough and sputum production, abnormal breath sounds compared with baseline, temperature >38 °C, chest radiograph demonstrating atelectasis or a new infiltrate, and physician documentation of atelectasis or pneumonia.

Surgery and anesthesia involve risk of PPCs to a degree that depends on the patient, anesthetic, and surgical factors [5]. Anesthesia changes the balance of forces between the chest wall and the lungs, leading to reduction in lung volume and compliance, which results in greater predisposition to alveolar collapse and the development of atelectasis [6], especially in the dependent parts of the lung. On a secondary plane, ventilation-perfusion mismatching is exacerbated, leading to impaired gas exchange and hypoxemia. Anesthetic management strategies can contribute to either the development or attenuation of PPC risk. Administering oxygen at a concentration over 80 %, for example, predisposes the patient to alveolar collapse, whereas some intraoperative ventilation strategies have been thought to play a role in reducing the incidence of PPCs [7].

There are a number of risk factors that have been identified that increase the likelihood of developing a PPC. The greatest preoperative risk factor are age >50 years, American Society of Anesthesiologists score >2, chronic obstructive pulmonary disease (COPD), congestive heart failure, functional dependence, and smoking. Obstructive sleep apnea is new to the list, but results in only a minor increase in the risk of PPC. Asthma and obesity do not appear to increase the risk substantially. The intraoperative risk factors are surgical site, duration of surgery, anesthetic technique, and emergency surgery. An upper-abdominal incision, close to the diaphragm, is the greatest PPC risk factor. From a procedural perspective, open aortic repair, thoracic surgery, head and neck surgery, and neurosurgery are associated with increased risk. Surgery longer than 3 h, general anesthesia, use of neuromuscular blocking agents, and emergency surgery are associated with more frequent complications. Perioperative blood transfusion does not appear to increase risk [8].