Postoperative pulmonary complications: An update on risk assessment and reduction

SUMMARY

There have been a number of significant recent developments in the perioperative management of pulmonary complications:

• Obstructive sleep apnea has been confirmed as a risk factor, and pulmonary hypertension has emerged as a novel risk factor.
• An updated respiratory failure index has emerged as a useful research tool to identify high-risk patients and to ensure uniform risk stratification in future research.
• Evidence has mounted for the effectiveness of several risk-reduction strategies, including the use of laparoscopic procedures for bariatric surgery; selective use of nasogastric tubes; postoperative thoracic epidural analgesia; and intensive preoperative inspiratory muscle training.

DISCUSSION

Question from the audience: I do preoperative evaluations in an orthopedic ambulatory surgery center. Our surgeons often tell me, “Just order preoperative pulmonary function tests,” or, “Get a blood gas.” How should I respond?

Dr. Smetana: This is an area of some controversy, but in general, spirometry does not add much to a preoperative risk assessment that is based on a history and physical exam. Usually if the spirometry is abnormal, it will not be a surprise after careful clinical assessment. Arterial blood gases have no role in routine preoperative assessment.

Question from the audience: A chest x-ray is often requested preoperatively, but is it a necessary study?

Dr. Smetana: The data for preoperative chest x-rays are fairly poor and don’t allow us to assess whether they accurately predict complication rates. Most studies on chest x-rays have looked at how they affect preoperative management—eg, whether they change the anesthesia or even the surgery—and have shown that preoperative management changes in only about 1% to 2% of cases. So the chest x-ray is a fairly low-yield test in this setting.

One could argue that a preoperative chest x-ray might provide a baseline for postoperative comparison, but actually it is not usually helpful in this regard. Having a baseline does not make it easier to correctly diagnose pneumonia postoperatively, for example. Abnormal chest x-rays correlate with higher risk, but most patients with abnormal films would be suspected of being at higher risk anyway based on findings from the clinical assessment.

Question from the audience: Many primary care doctors in my hospital screen patients for pulmonary hypertension, but this raises the question of what to do with any information gained. What do you tell patients? Anesthesiologists?

Dr. Smetana: I don’t recommend preoperative screening for pulmonary hypertension unless there is some specific clinical reason to look for it. We don’t know if the perioperative risks that I described for patients with diagnosed or symptomatic pulmonary hypertension would also apply to patients with unrecognized, asymptomatic pulmonary hypertension that happened to be identified by screening.

Patients with pulmonary hypertension are at very high risk, especially for respiratory failure. But we don’t have any risk-reduction strategies specific to these patients, although I would recommend applying the general risk-reduction strategies that I discussed.

Question from the audience: I saw a man at my high-risk preoperative clinic who scored normally on a 6-minute walk test but then was found sound asleep when I was ready to see him a little while later. I suspected he had undiagnosed sleep apnea, and therefore had an increased risk of postoperative pulmonary complications, but what evidence would I have to delay his surgery to diagnose the sleep apnea and stabilize him on CPAP?

Dr. Smetana: For a patient with clinically suspected but undiagnosed sleep apnea, we have some evidence that the diagnosis should be pursued before surgery is performed.⁸ If the surgery were elective, it would be appropriate to have the patient evaluated and, if obstructive sleep apnea were diagnosed, treated in the customary way with CPAP. For patients who are hospitalized after surgery, CPAP can be continued as soon as possible in the hospital.

I would not have made this recommendation a few years ago, but now the evidence is more compelling. However, at this point I would not recommend routine preoperative screening of all patients for sleep apnea. Ongoing research is looking at this question.

Follow-up question: How long should surgery be delayed to optimize the patient on CPAP?

Dr. Smetana: Risk for postoperative respiratory failure is reduced very quickly after initiating CPAP therapy. A week would probably be sufficient, but there are no good data to specifically address that question.

Question from the audience: What about patients with asthma who are undergoing surgery—which ones benefit from stress-level steroids and preoperative nebulizer therapy?

Dr. Smetana: Surprisingly, asthma—if well controlled—is not a risk factor for postoperative pulmonary complications. Patients within 80% of their predicted or personal best peak flow appear to have a risk similar to that of patients without asthma. For patients with uncontrolled or poorly controlled asthma, the general rule is the same as for patients with COPD: treat them the same as if they weren’t having surgery. If a patient with asthma has a clinical indication for cortico­steroids based on his or her condition, give cortico­steroids whether or not surgery is planned. Corticosteroids are safe and do not raise the risk of postoperative wound complications. But we have no evidence to support routine use of steroids for all patients with asthma simply because elective surgery is planned.

Follow-up question: Do you optimize poorly controlled patients with oral prednisone for several days preoperatively, or do you use a stress protocol?

Dr. Smetana: For a patient whom you would normally treat with an outpatient course of prednisone, you should do just that. For a patient with an exacerbation severe enough to require admission for intravenous steroids and inhaled nebulizer therapy, then you should use that strategy. If the surgery is elective, it should be delayed until the patient is at his or her personal best.