Although pulmonary complications are not as well studied as cardiac complications in the postoperative setting, they are just as common following noncardiac surgery and are even more costly. It is worthwhile to identify surgical patients most at risk of postoperative pulmonary complications and take measures known to mitigate risk. This paper discusses important risk factors to identify during a preoperative pulmonary evaluation and then focuses on recent advances in strategies for reducing postoperative pulmonary complications. Teaching questions are included throughout, along with the rationale behind their answers.
POSTOPERATIVE PULMONARY COMPLICATIONS: WHAT ARE WE TRYING TO PREVENT AND WHY?
The definition of postoperative pulmonary complications is more variable and less intuitive than that of cardiac complications. Cardiac complications—postoperative myocardial infarction, cardiac death, and pulmonary edema—are more consistently defined and measured in clinical trials. Studies of postoperative pulmonary complications often group together pneumonia, respiratory failure, atelectasis, bronchospasm, and exacerbation of chronic obstructive pulmonary disease (COPD), making it more difficult to individually evaluate risk factors for different outcomes.
There are several reasons why it is important to consider pulmonary risk when evaluating patients preoperatively:
Pulmonary complications are as common as cardiac complications following noncardiac surgery. For example, in a secondary analysis of the cohort of noncardiac surgical patients used to validate the Revised Cardiac Risk Index,1 Fleischmann et al found that the incidence of pulmonary complications (2.7%) was highly comparable to that of cardiac complications (2.5%).2
Respiratory failure is a marker of ill health and predicts further complications. Postoperative respiratory failure (often defined as the need for ventilation for more than 48 hours after surgery) is an extremely morbid event. Johnson et al compared the outcomes of patients with and without respiratory failure as a complication of surgery.3 Among patients with respiratory failure, 26% died within 30 days, 6% had a myocardial infarction, 35% developed pneumonia, 10% developed acute renal failure, and 3% developed a deep vein thrombosis or pulmonary embolism; in contrast, rates of each of these events were lower than 2% among patients without respiratory failure.
Pulmonary complications are expensive and require lengthy hospitalization. The National Surgical Quality Improvement Program (NSQIP) compared hospitalization costs and length of stay among patients with various postoperative complications.4 Among infectious, cardiovascular, venous thromboembolic, and pulmonary complications, pulmonary complications were by far the most costly and, along with venous thromboembolic complications, required the longest mean hospital stay.
For these reasons, identifying patients at risk for pulmonary complications and developing a strategy to reduce the risk is clearly worthwhile.
IDENTIFYING RISK FOR PULMONARY COMPLICATIONS
Question: Which of the following is the most important risk factor for postoperative pulmonary complications?
A. High-risk surgical site
B. General anesthesia
The correct answer is A. Pulmonary complications differ from cardiac complications in an important way: procedure-related factors are more predictive of pulmonary complications than are patient-related factors. Even healthy patients undergoing high-risk surgery are at risk for pulmonary complications. As for the other answer choices, general anesthesia and COPD are risk factors but are not as important as surgical site, and obesity has not been shown to be a risk factor at all.
Take-home points from the 2006 ACP guideline
Patient-related risk factors. As noted in Table 1, the most important patient-related risk factors identified in the ACP guideline are increasing age and increasing American Society of Anesthesiologists (ASA) classification of comorbidity.
The effect of advanced age becomes particularly notable around age 60 years and escalates from there. This effect of age differs from that for cardiac complications, for which age drops out as a risk factor after adjustment for other diseases and risk factors. For pulmonary complications, in contrast, even older patients who are healthy are at increased risk.
The ASA classification is a general index of overall morbidity that ranges from class 1 (normal healthy patient) to class 5 (moribund patient who is not expected to survive without the operation).
Notably, COPD and smoking were only minor risk factors in the ACP analysis.
Procedure-related risk factors. Surgical site was found to be the most important of any of the patient- or procedure-related risk factors. The closer the incision is to the diaphragm, the greater the risk for pulmonary complications. Aortic, thoracic, and abdominal procedures carry the highest risk (Table 1), and among abdominal procedures, upper abdominal surgery (eg, cholecystectomy) is riskier than lower abdominal surgery (eg, gynecologic).
Other procedure-related risk factors identified were emergency surgery, surgery lasting more than 3 hours, use of general anesthesia, and multiple transfusions (Table 1).