ostoperative pulmonary complications (PPCs) are defined as pulmonary abnormalities that produce identifiable disease or dysfunction that is clinically significant and adversely affects the clinical course of the patient. Such complications include pneumonia, respiratory failure requiring mechanical ventilation for more than 48 hours after surgery, atelectasis and exacerbation of pre-existing chronic lung disease.

PPCs are as prevalent as cardiac complications and contribute similarly to morbidity, mortality and increased length of stay. Pulmonary complications may even be more likely than cardiac complications to predict long-term mortality after surgery.^1-4 The risk of PPC is highest among patients undergoing coronary artery bypass grafting (CABG), thoracotomy, head and neck surgery and abdominal surgery, where up to 40 percent of patients suffer some form of PPC.^1-2,4

Risk Factors
The risk factors for PPCs can broadly be classified as patient-related or procedure-related factors [Table 1,]. The patient-related risk factors include age, ASA Physical Status, functional status, presence of chronic obstructive pulmonary disease (COPD) and congestive heart failure (CHF). Procedure-related risk factors are primarily related to surgery site, duration of surgery and whether surgery is emergent or elective. Additionally, serum albumin level less than 3.5 mg/dL is also considered a risk factor.^4,5 Interestingly, based on a recent American College of Physicians systematic review and guidelines for reducing PPC in non-cardiac surgery,⁴ diabetes mellitus, obesity, asthma and restrictive lung disease are not sufficiently supported by available evidence as risk factors for PPC. More research is needed to further define those risk factors (such as obstructive sleep apnea), which are thought to result in PPCs based on clinical experience but are not currently supported by available evidence.

In the perioperative period, several factors necessary for the safe performance of surgery result in physiologic changes that may contribute to PPCs. For example, the administration of general anesthesia results in the disruption of normal respiratory muscle activity beginning with induction of anesthesia and continuing into the postoperative period. The vital capacity is reduced by 50-60 percent and may remain decreased for up to one week after surgery, while functional residual capacity (FRC) is reduced by about 30 percent. Reduction of the FRC below closing volumes contributes to the risk of atelectasis, pneumonia and ventilation/perfusion mismatching. The residual effects of anesthesia and use of opioids for pain control in the postoperative period both depress the respiratory drive and can result in hypoventilation and atelectasis. Further, anesthetic-induced inhibition of cough and impairment of mucociliary clearance can result in increased risk of infection. Surgery-related respiratory dysfunction is additive to these physiologic changes. Abdominal and upper-abdominal surgery, for example, encourage a restrictive pulmonary physiology pattern and diminished vital capacity, while thoracic surgery is more likely to involve complications resulting from an interplay of factors such as inhibitory effects of volatile anesthetics on hypoxic pulmonary vasoconstriction and diminution of the hypoxic and hypercapnic ventilatory drives following opioid analgesics.^6-8

Risk Assessment
History and physical examination are the most important tools for evaluation and risk assessment for PPCs.⁹ Physical examination should be directed toward evidence for obstructive lung disease. Although laboratory tests serve as adjuncts to the clinical evaluation, they should be obtained only in selected patients. Pulmonary function tests (PFTs), arterial blood gas analysis and chest radiographs (CXR) should only be obtained to confirm findings on history and physical examination. Pulmonary function tests are not accurate predictors of PPC, but it is reasonable to obtain preoperative PFTs for unexplained dyspnea or exercise intolerance. Of note, hypercarbia is also not a useful predictor of PPCs. Although 2.5 to 37 percent of CXRs obtained as part of preoperative evaluation are abnormal, only 0 to 2.1 percent led to change in management in a systematic review.¹⁰ There are no controlled trials on the effectiveness of routine CXR. Therefore, preoperative CXRs should only be obtained in patients with pre-existing cardiopulmonary disease and those with symptoms or findings on physical examination that suggest likelihood of cardiopulmonary disease.¹¹ It is important to understand that no level of pulmonary function is an absolute contraindication to elective non-thoracic surgery that may result in a marked improvement in quality of life.¹¹

Risk Modification Strategies
Preoperative measures that can be taken to modify the risk of PPCs include preoperative smoking cessation. Smoking cessation should begin six to eight weeks before surgery. The perioperative period should be viewed as an opportunity to initiate permanent smoking cessation. ASA has formed a smoking cessation task force to remind smokers that quitting around the time of surgery can help to avoid complications and speed recovery time. The Society has also sought to increase public awareness through video news releases (VNRs) to television stations across the country explaining how stopping smoking can improve surgical outcomes. The VNRs also provide information on tools that can help patients to quit smoking for good.¹² Other preoperative measures that can modify the occurrence of PPCs include appropriate treatment of airway obstruction and infection in patients with COPD. Non-urgent or elective surgery should be delayed until infection has cleared. Secretion clearance should also be optimized preoperatively by a trial of chest physiotherapy (CPT) and patient education regarding use of incentive spirometry and proper coughing techniques after the inhalation of bronchodilators. A recent study by Hulzebus et al.¹³ found that preoperative inspiratory muscle training reduced the incidence of PPCs and duration of postoperative hospitalization in patients at high risk of developing a pulmonary complication undergoing CABG surgery.

Intraoperative strategies employed to prevent PPCs should include avoidance of long-acting neuromuscular blockers (e.g., pancuronium) as well as deep muscle relaxation, which should reduce the incidence of postoperative residual muscle paralysis. Patients with residual muscle paralysis have been reported to be approximately three times more likely to develop PPCs. Compared with long-acting muscle relaxants, intermediate-acting muscle relaxants are associated with a lower incidence of PPCs with or without prolonged neuromuscular blockade.¹⁴

Other intraoperative strategies to consider include the use regional anesthetic techniques, minimally invasive surgical approach (e.g., laparoscopic surgery) when possible, and limiting the duration of surgery to less than three hours. Scheduling the surgical procedure later in the day to allow the patient sufficient time to clear overnight accumulated secretions before administering preoperative medications may also be helpful in patients with pre-existing pulmonary conditions. The evidence for these strategies is not clear, and further studies are needed.

Postoperative strategies that include deep-breathing exercises or incentive spirometry in high-risk patients have been found to be useful in preventing PPCs. Frequent deep breathing to prevent atelectasis and coughing to clear secretions should be encouraged. Although incentive spirometry is a convenient technique used to encourage deep breathing, continuous positive airway pressure has been reported to decrease the incidence of severe complications in patients who develop hypoxemia after elective major abdominal surgery.¹⁵ Most importantly, attention to postoperative analgesia is critical to allow effective coughing, as is extubation of the patient’s trachea as soon as possible to restore the patient’s ability to cough.

CPT is a form of airway clearance therapy that can be used to treat post-surgical patients with evidence of ineffective secretion control, especially patients with pre-existing pulmonary disease. Many randomized controlled trials^16-18 have demonstrated significant reductions in both atelectasis and PPCs in patients treated with CPT after abdominal and cardiothoracic surgery. Unfortunately, many critically ill or major surgery patients do not have the energy, lung capacity or respiratory muscle strength for techniques such as CPT, which depends on forced expiration or positive end-expiratory pressure devices. CPT through percussion and postural drainage can be used in these cases. Finally, early postoperative ambulation is especially helpful in the prevention of PPCs.

Interestingly, nutritional supplementation using total parenteral nutrition aimed at improving hypoalbuminemia has no advantage over total enteral nutrition or even no supplementation in reducing PPCs.⁴ Routine use of nasogastric tubes after surgery until gastrointestinal motility returns confers no advantage and is therefore discouraged. In fact, patients receiving selective nasogastric decompression had a significantly lower rate of pneumonia and atelectasis with no difference in aspiration rates.^4,19 Nasogastric tubes should be used selectively only in cases of severe postoperative nausea or vomiting, inability to tolerate oral intake or symptomatic abdominal distention.²⁰

In summary, a good understanding of the risk factors leading to the development of PPCs should result in the implementation of perioperative strategies designed to prevent their occurrence and reduce severity.

References:
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Adebola Adesanya, M.D., M.P.H., is Associate Professor of Anesthesiology, University of Texas Southwestern Medical Center, Dallas.