Postoperative pulmonary complications are defined as pulmonary abnormalities occurring in the postoperative period that produce clinically significant identifiable disease or dysfunction that adversely affect the clinical course. The incidence of these complications ranges from 2 to 100% in various series, depending on predisposing risk factors as well as the specific surgical procedure (Table 11.1). Taken together, they are more common than postoperative cardiac complications, lead to longer hospital stays (22.7 vs. 10.4d), and increase the relative risk of death to 14.9 (95% confidence limits 4.76–26.9), particularly due to pneumonia. Factors associated with an increased risk for postoperative pulmonary complications include the following: surgical site prolonged duration of surgery underlying lung disease smoking history (> 20 pack years) obesity (BMI > 25) poor nutritional status age > 60 years ASA > 3 inadequate nurse staffing in postoperative care areas. Patients should be evaluated preoperatively to identify these factors and efforts made to improve risk status. Preoperative respiratory assessment and management are discussed elsewhere. The pathogenesis of pulmonary complications in the postoperative period has been well described. Hypoventilation and reduced lung volumes beginning with anesthesia and surgery combine to produce atelectasis and predispose to respiratory tract infection. Immobility leads to higher risk of thromboembolic disease. Respiratory muscle dysfunction is common, especially following cardiac, chest, or upper abdominal operations. Cardiac surgeries are associated with a 10%–85% incidence of phrenic nerve dysfunction due to phrenic nerve injury, either by cold injury or by direct operative damage.