Postoperative pulmonary complications are common, especially in elderly patients with comorbidities. Nearly 5% of all patients undergoing noncardiac surgery experience significant pulmonary complications.[1] Postoperative pulmonary complications include respiratory failure, pneumonia, and atelectasis. Risk factors that can be assessed at the bedside include the following:

• Advanced age (e.g., age greater than 65 years increases the risk of complication 4.7-fold or by 370%).

• Smoking history (e.g., smoking history of longer than 40 or more pack-years increases the risk 5.7-fold or by 470%).

• A history of COPD (this increases the risk 4.2-fold or by 320%).

• Obesity (body mass index greater than 30 kg/m2 increases the risk 4.1-fold or by 310%).

• A positive cough test (see Table 1 [9]; this increases the risk 4.3-fold or by 330%).

• Maximal laryngeal height of 4 cm or less (this increases the risk 6.9-fold or by 590%).

• A forced expiratory time of 9 seconds or more (this increases the risk 5.7-fold or by 470%). 

• Surgical time of 2.5 hours or more (this increases the risk 2.9-fold or by 190%).[2] 

Identification of any risk factors should prompt clinicians to perform laboratory tests for additional risk information (Table 2 [10]). These tests include spirometry and arterial blood gas assessment (on room air if pos­sible). An FEV1 (forced expiratory volume in 1 second) of less than 1 L increases the risk of postoperative pulmonary complications 7.9-fold or by 690%, while an FVC (forced vital capacity) value of less than 1.5 L in­creases the risk 11.1-fold or by 1000%. 

Hypercarbia (defined as PaCo2 of 45 mm Hg or greater) on arterial blood gas assessment increases the risk 61-fold, while hypoxemia (de­fined as PaCo2 of less than 75 mm Hg) increases the risk 13-fold.[2] Abnormalities identified by spirometry or arterial blood gas assessment (or both) are “red flags” and mean respiratory consultation should be sought before the operation to further assess risk for the patient.

Postoperative pneumonia risk index
One of the most important postoperative pulmonary complications is pneumonia. The risk factors already listed can be used as guides in risk stratification for this complication. 

A more formal method involves the postoperative pneumonia risk index, developed by Arozullah and colleagues for patients undergoing major noncardiac surgery (Table 3 [11]).[1] In this index, point values are assigned to each of 14 variables and the points are added to come up with a score out of 84. 

This score is then used to estimate the patient’s risk for postoperative pneumonia according to five classes of risk, with class 5 being the highest (Table 4 [12]). A major limitation of this index is the absence of arterial blood gas and spirometry values. 

Nevertheless, the index does help stratify risk and is a useful way to identify high-risk patients who are likely to benefit from aggressive postoperative intervention.

Interventions to reduce complications 
Smokers should be advised to discontinue smoking at least 2 months before surgery (Table 5 [13]). Any patients with spirometric evidence of asthma or COPD should be treated aggressively with bronchodilators and inhaled corticosteroids prior to surgery, and any significant exacerbations should be treated with appropriate antimicrobials and systemic corticosteroids. 

Postoperatively, patients in risk class 3 or higher should be treated with lung expansion modalities such as deep breathing exercises, incentive spirometry, or continuous positive airway pressure. These modalities are equally efficacious in reducing the risk of postoperative pulmonary complications by nearly 50%. 

For patients who experience abdominal distension postoperatively, a nasogastric tube can be used judiciously to decompress the abdomen. If at all possible, pa­tients should receive epidural analgesia with local anesthestics rather than systemic opioids, which have the potential to depress the respiratory centre and contribute to postoperative pulmonary complications.

Conclusions
Postoperative pulmonary complications are common following thoracic or abdominal surgery. A comprehensive bedside assessment coupled with spirometry and arterial blood gas assessment can identify patients at high risk, who may then be referred for more comprehensive risk assessment through specialty clinics. 

Smokers should be advised to quit smoking at least 2 months before surgery. Postoperatively, lung expansion modalities should be used to reduce the risk of postoperative pulmonary complications. 

For patients at high risk of postoperative complications, epidural analgesia with local anesthetics or analgesics should be used whenever possible in lieu of systemic narcotics or other respiratory depressants.

Competing interests
Dr Sin has received honoraria for speaking from GlaxoSmithKline (GSK), research funding from GSK, AstraZeneca, and Boeh­ringer Ingelheim, and served as a consultant to GSK and AstraZeneca.

Dr Sin is an associate professor in the Department of Medicine at the University of British Columbia, a staff respirologist at St. Paul’s Hospital, and a Canada Research Chair in COPD.