Home Feature Screening for pulmonary complications of surgery: a look at the evidence

Screening for pulmonary complications of surgery: a look at the evidence

August 2006

Published in the August 2006 issue of Today’s Hospitalist

While physicians tend to focus on the cardiac complications of surgery, the reality is that pulmonary complications often represent a similar “or larger “risk for patients undergoing noncardiac surgical procedures.

From prolonged mechanical ventilation to atelectasis and the exacerbation of pre-existing COPD, pulmonary problems from surgery represent a significant threat to patients. But the good news is that many of these problems can be prevented or minimized with the right strategies.

At the American College of Physicians’ annual meeting, which was held earlier this year in Philadelphia, Gerald W. Smetana, MD, presented the results of an exhaustive review of the research examining postoperative pulmonary complications. That process, which looked at more than 300 studies, was used to create new ACP guidelines that were published in the April 18, 2006, Annals of Internal Medicine.

In reviewing decades of medical literature on pulmonary problems from surgery, Dr. Smetana and his team focused on a number of factors, including general health status, age, obesity, obstructive sleep apnea, COPD and smoking. During his presentation at the ACP’s meeting, Dr. Smetana, a general internist at Beth Israel Deaconess Medical Center and an associate professor of medicine at Harvard Medical School, discussed two basic types of risk factors “patient-related and procedure-related “as well as strategies to prevent pulmonary complications.

Patient-related risk factors

Does a patient’s general health status predict risk? While the answer may seem obvious, Dr. Smetana presented data to help quantify how overall health may impact the risk of pulmonary complications after surgery.

He said that several studies have found that the guidelines developed by the American Society of Anesthesi¬ologists (ASA) to assess postoperative mortality are a good predictor of postoperative pulmonary complications. Studies have shown that an ASA classification of greater than two confers a three- to five-fold increase in risk of pulmonary complications. Dr. Smetana said that held true even after researchers made adjustments for other factors.

“The literature also shows that functional dependence, meaning the need to have somebody else assist in per¬forming the activities of daily living, puts a patient at higher risk,” Dr. Smetana explained.

Here’s a look at some of the other patient-related risk factors Dr. Smetana reviewed during his presentation:

“¢ Age. While age is not generally considered to be a risk factor for cardiac complications, Dr. Smetana’s analysis found that advanced age is a substantial, independent risk factor for postoperative pulmonary complications, even after adjusting for comorbidities that are more common with advancing age.

“¢ Obesity. Surprisingly, obesity “even morbid obesity “does not appear to be a risk factor for postoperative pulmonary complications. Of eight studies that Dr. Smetana reviewed that focused on obesity as a predictor of pulmonary complications, only one found obesity was a risk factor like obesity and smoking cessation, recent research offers some surprises

“Even for patients undergoing bariatric surgery,” Dr. Smetana noted, “the literature showed no differences in outcomes when patients were stratified by their body mass index. As a result, physicians should not consider obesity a contraindication for high-risk surgery solely due to concern for pulmonary complications.” Obesity is, however, a risk factor for postoperative venous thromboembolic complication, but that is a separate discussion.

“¢ Sleep apnea. Obstructive sleep apnea appears to be a predictor of pulmonary problems. A study at the Mayo Clinic showed that patients with obstructive sleep apnea had longer lengths of stay and more unplanned transfers to the ICU. Dr. Smetana pointed out, however, that the study did not show specifically that there were increased pulmonary complications.

Nevertheless, he added, obstructive sleep apnea remains an important risk factor, particularly for anesthesiologists, because of the increased risk of airway issues during the immediate postoperative period.

“¢ COPD. According to Dr. Smetana, chronic obstructive pulmonary disease (COPD) is an important risk factor for postoperative pulmonary complications. One study showed that patients exhibiting one of several factors on physical exam have as much as a six-fold increased risk for pulmonary complications. Those factors are decreased breath sounds, prolonged expiration, rales, wheezes and rhonchi.

“¢ Smoking cessation. A number of studies reviewed by Dr. Smetana and colleagues examined the effects of smoking and smoking cessation before surgery to determine the risk of postoperative pulmonary complications. “Surprisingly,” he noted, “several studies have shown that patients who stop smoking one to eight weeks prior to surgery have a significantly higher risk of complications.”

For example, in one study of current smokers, the rate of complications was 33 percent. Among non-smokers, by comparison, the rate was 11 percent. But among recent quitters, the risk for complications jumped to 57 percent.

Dr. Smetana noted that studies that looked at a range of high-risk surgeries such as abdominal and cardiac surgery found similar results.

“There may be a mechanism with increased sputum production in the first two months after quitting, which could potentially increase risk,” he explained. “There may also be an issue of self-selection in the studies. Patients who correctly perceive themselves to be at higher risk may be more likely to try to quit.”

“¢ Other factors. Other patient-related factors for pulmonary complications include abnormal chest X-rays, congestive heart failure, impaired sensorium or altered mental status. The evidence for abnormal chest X-rays is not compelling and based on limited data from two studies. Heavy alcohol use appears to be a minor independent risk factor for pulmonary complications.

Procedure-related risk factors

According to Dr. Smetana, procedure-related risk factors are a more significant predictor of pulmonary complications than patient-related risk factors.

His team found that the single most important predictor of postoperative pulmonary complications is surgical site. In general, his analysis found, the closer the incision is to the diaphragm, the higher the risk.

“In our pooled analysis, we found the risk rates were 20 percent in upper abdominal and only 8 percent in lower abdominal,” Dr. Smetana reported. “Among thoracic surgeries such as esophagectomy but not including resective surgeries, we found the risk rates were 20 percent to 40 percent. The risk rate was 25 percent for major vascular surgeries involving the aorta.”

Dr. Smetana also said that prolonged surgeries “procedures that are longer than three hours “almost double the rate of pulmonary complications. Other risk factors included the use of long-acting neuromuscular blockers such as pancuronium and general anesthesia, as well as emergency surgery and the routine use of postoperative nasogastric tubes.

Testing strategies

To minimize both patient- and procedure-related pulmonary complications after noncardiac surgery, Dr. Smetana reviewed the evidence that was used to create the ACP’s guidelines.

While existing guidelines recommend spirometry for all patients about to undergo lung resection surgery, he said that spirometry should not be routinely used before nonresective surgery. He acknowledged that the recommendation may come as something of a surprise, but he explained that the data raise questions about the role of spirometry.

“After reviewing the results of many relevant studies, we concluded that there was insufficient evidence to determine if abnormal results of spirometry predict risk or, in fact, increase risk,” Dr. Smetana explained.

While some studies have found abnormal spirometric results to increase risk, he said, few studies have compared results of spirometry to clinical evaluation. In general, patients with abnormal spirometry would not escape clinical detection and abnormal results from spirometry generally would confirm the clinical impression of risk.

While spirometry may not be particularly helpful in stratifying risk, Dr. Smetana pointed to data that have shown that two commonly used blood tests are helpful in identifying high-risk patients. Data show that an albumin level of less than three or a BUN greater than 30 indicate a higher risk. In fact, Dr. Smetana said, a low albumin level turned out to be one of the most predictive factors of pulmonary complications after noncardiac surgery.

Risk-reduction strategies
Once patients have been identified as having a high risk of pulmonary complications, what can physicians do to reduce that risk? Dr. Smetana reviewed several commonly used strategies and the evidence behind each.

“¢ Spirometry/deep breathing exercises. Dr. Smetana said that lung expansion maneuvers are the most effective strategy to reduce risk. He explained that the physiologic mechanism for postoperative pulmonary complications is a decrease in lung volumes that results from surgery and anesthesia. Strategies that minimize the expected reduction in lung volumes, he explained, can reduce complication rates.

He noted, however, that there is no evidence to suggest that a particular lung expansion maneuver is superior to others.

“¢ CPAP. Another effective strategy is continuous positive airway pressure (CPAP), which can increase lung volumes after surgery and therefore reduce complications. “Unfortunately, this is more labor intensive, more expensive, and there’s a small risk of barotraumas,” said Dr. Smetana. “Because CPAP is not effort-dependent, we recommend that clinicians use this in patients who cannot cooperate with incentive spirometry or deep breathing exercises.”

“¢ Pain control. Another intervention that may reduce postoperative pulmonary complications is pain control. Dr. Smetana presented the results of a meta-analysis of studies that compared different pain control strategies such as subcutaneous morphine, epidural opioids, epidural local anesthetics and intercostal blocks.

“Each of these strategies reduces the relative risk of pneumonia and all postoperative pulmonary complications slightly,” he explained, “but the only one that was statistically significant was the postoperative epidural local anesthetics. Among intraoperative strategies, short-acting neuromuscular blockers reduce the risk of postoperative residual neuromuscular blockade and hypoventilation and therefore can reduce the risk for pulmonary complication rates.”

While there is reasonable evidence to suggest that epidural or spinal anesthesia, short-acting neuromuscular blockade and potentially intercostal blocks may help reduce the risk of complications, that evidence was mixed for laparoscopic when compared to open surgery. Similarly, the evidence for risk reduction by using intraoperative neuraxial blockade, postoperative epidural analgesia or immunotrition was insufficient to make a recommendation.

“¢ NG tubes. The use of nasogastric decompression after abdominal surgery can potentially increase the risk for aspiration, Dr. Smetana said, increasing the risk for postoperative pulmonary complications.

“NG tubes can be used routinely for every patient undergoing abdominal surgery or selectively based on symptoms such as nausea or abdominal distention,” explained Dr. Smetana. “In a meta-analysis of nearly 30 recent studies, there was a trend towards a decrease in pulmonary complications among patients who received a nasogastric tube selectively rather than as a routine practice.”

“¢ Optimizing COPD. Dr. Smetana said that optimizing COPD appeared to be an effective risk-reduction strategy. “Optimizing COPD in essentially the same fashion as you would if the patient wasn’t having surgery may reduce the risk of complications,” he explained. “That can include corticosteroids, if they’re indicated based on the patient’s clinical status.” A brief course of systemic corticosteroids before surgery does not increase the risk of respiratory infection or wound complications.

Finally, Dr. Smetana said that there is fair evidence suggesting that several interventions are ineffective, including total parenteral nutrition, total enteral nutrition and right heart catheterization.

Michael Krivda is a freelance writer specializing in health care. He is located in Perkasie, Pa.