A comprehensive preoperative evaluation must include assessment of the risk of postoperative pulmonary complications. While few would argue this point, pulmonary risk is often underappreciated as clinicians typically focus the majority of their energy on the preoperative cardiac evaluation. Highlighting the risk of this approach, postoperative pulmonary complications occur with similar frequency and greater morbidity than cardiovascular complications.

Clinicians intuitively recognize several risk factors for pulmonary complications, but some predictors of postoperative respiratory problems are not obvious. Additionally, clinicians may struggle with the appropriate utilization of preoperative pulmonary diagnostic testing. Recently published risk indices and practice guidelines provide valuable assistance in the identification of risk factors and the performance of evidence-based preoperative evaluation.

Pulmonary complications following anesthesia and surgery result from central nervous system suppression and altered respiratory dynamics. Administration of sedating agents and neuromuscular blockade exposes the patient to the risk of aspiration. Furthermore, regardless of the type of anesthetic technique utilized, patients will experience a reduction in lung volumes perioperatively. Reduction in lung volumes is the primary mechanism that may lead to atelectasis and predispose a patient to the additional complications of pneumonia and respiratory failure. This reduction in lung volumes is greatest for patients undergoing thoracic and upper abdominal surgery. Table 55-1 lists specific postoperative pulmonary complications and diagnostic considerations for each.

Several different patient characteristics increase postoperative pulmonary risk (Table 55-2). While most of these patient-specific factors are nonmodifiable, their identification is important for providing patients, surgeons, and anesthesiologists with an accurate assessment of perioperative risk and to identify patients for whom one should employ risk reduction strategies.

Chronic Lung Disease

Multiple studies have identified chronic obstructive pulmonary disease (COPD) as a major risk factor for postoperative respiratory problems. In a recent systematic review, authors reported COPD to be a significant predictor of postoperative pulmonary complications; the pooled odds ratio was 1.79. Surprisingly, the risk attributable to COPD was lower than other patient-related risk factors. Other forms of chronic lung disease, including interstitial lung diseases and obesity hypoventilation syndrome, have not been sufficiently studied to definitively determine their impact on perioperative pulmonary risk. However, pulmonary hypertension has recently been shown to increase the risk for both postoperative pulmonary complications and perioperative mortality.

Advanced Age

Advanced age is a more important predictor of pulmonary complications than COPD. Contrary to previous belief, this risk is not a result of the cumulative morbidities associated with aging. After adjustment for these additional risk factors, age greater than 59 has an odds ratio of 2.09, whereas age greater than 69 carries an odds ratio of 3.04. Recognition of age, even in the absence of other comorbidities, as an important source of pulmonary risk is critical as the population ages and more elderly patients undergo surgical procedures. The consequence of these observations is that even healthy older patients are at risk for postoperative pulmonary complications. This stands in contrast to postsurgical cardiac complications, which are not more common among older patients after adjusting for comorbidities.

Smoking

Cigarette smoking increases the risk of postoperative pulmonary complications, but the degree of risk elevation is actually less than that from COPD and age. Clinicians should consider a recent history of cigarette smoking to be at least a moderate predictor of pulmonary risk.

Medical Comorbidities

As the number of comorbid illnesses increases, so does the risk of perioperative complications. The American Society of Anesthesiologists (ASA) classification system is easy to use and predicts the risk of postoperative respiratory problems as well as overall morbidity and mortality. Compared with ASA class I patients (no comorbidities), patients with an ASA class of II or greater have a nearly fivefold increase in the rate of postoperative pulmonary complications. The risk increases with each higher ASA class.

Functional Status

Large multivariate studies have also identified dependence on others for assistance with activities of daily living as a significant risk factor for postoperative pulmonary complications. The contribution of functional dependence to perioperative pulmonary risk is similar to that of cigarette smoking and chronic lung disease.

Congestive Heart Failure

Congestive heart failure (CHF) is not only an obvious risk factor for perioperative cardiac complications but also a predictor of postoperative respiratory failure. Although the cause of respiratory failure may be CHF-related pulmonary edema, a history of CHF is nonetheless an independent risk factor for pulmonary complications with a relative risk estimated at 5.7 in the geriatric population.

Other Risk Factors

In addition to the previously described risk factors, several other patient characteristics have been less clearly linked to postoperative pulmonary complications. For instance, abnormal findings on chest examination and abnormal chest radiography have been associated with increased pulmonary risk in smaller, older studies but not in more recent large-scale multivariate analyses. Consumption of more than two alcoholic drinks per day within 2 weeks of surgery, recent weight loss exceeding 10% of total body weight, chronic corticosteroid use, preoperative transfusion of more than 4 units of blood, acute alteration of mental status, and a history of stroke were modest risk factors for postoperative pneumonia in the largest prospective study to date.

The role of obstructive sleep apnea (OSA) in postoperative complications has long been intuited but not confirmed in objective studies. In at least one study, OSA patients showed an upward trend in reintubation, hypercapnia, and hypoxemia as well as a statistically significant increase in unplanned intensive care unit (ICU) admissions. Other recent studies also suggest that patients identified as being at risk for but not formally diagnosed with OSA have an increased risk of postoperative pulmonary complications. For example, patients with at least two clinical features of OSA (snoring, crowded oropharynx, daytime somnolence, or witnessed apneas) who have abnormal overnight oximetry are more likely to develop postoperative hypoxemia or airway management problems than patients without these features. Until more data are available, it is reasonable to consider OSA at least a moderate risk factor for perioperative respiratory problems.

Factors Not Associated with Increased Pulmonary Risk

Notably absent from the described risk factors are four conditions often mistaken as predictors of postoperative pulmonary complications: well-controlled asthma, obesity, diabetes mellitus, and immunosuppression. Although a potential relationship between perioperative pulmonary risk and morbid obesity or asthma has been assumed by some clinicians, multivariate investigations have consistently found no such correlation. The current literature provides little data on the contributions of immunosuppression and diabetes mellitus to pulmonary surgical complications.