What every physician needs to know:

Postoperative respiratory complications are a significant cause of morbidity and mortality after surgery. Effective management of patients at risk for postoperative complications after surgery requires knowledge of the predictable changes in pulmonary physiology that are associated with surgery and anesthesia, awareness of the factors that may increase a patient’s risk for development of postoperative respiratory compromise, and application of evidence-based strategies to reduce these complications in at risk individuals.

Although several risk calculators are available, a careful history and physical examination remain the essential elements of preoperative pulmonary evaluation. A number of interventions, both before and after surgery, may help to minimize the risk of postoperative pulmonary complications. However, the focus of care in all patients after surgery is close monitoring and early detection of emerging respiratory complications.

This review will discuss the routine pulmonary preoperative evaluation for patients undergoing noncardiothoracic surgery. A discussion of the preoperative pulmonary examination and evaluation for patients undergoing cardiothoracic surgery, such as lung resection and lung or cardiac transplantation, is beyond the scope of this article.

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Classification

While the list of potential postoperative pulmonary complications is long, most notable among them are the following:

  • Acute respiratory failure

  • Atelectasis

  • Pneumonia

  • Aspiration pneumonitis

  • Transfusion-related acute lung injury (TRALI) and transfusion-associated circulatory overload (TACO)

  • Exacerbation of pre-existing lung disease

  • Pleural effusion

  • Phrenic nerve injury

  • Pulmonary embolism

  • Obstructive sleep apnea (OSA)

How and/or why did the patient develop a postoperative pulmonary complication?

Many postoperative respiratory complications are an exaggerated manifestation of expected postoperative changes in pulmonary function that are the result of the surgery itself, anesthesia, or various pharmacologic interventions. These include the following:

A Restrictive Pattern of Pulmonary Function

The restriction is manifested by moderate to severe reductions in the vital capacity (VC) and smaller but more important reductions in the functional residual capacity (FRC) after thoracic and abdominal surgery. These findings may persist for up to a week or more after surgery. The restrictive physiology appears to be due in large part to diaphragm dysfunction. The derangement increases the risk of atelectasis, which may worsen oxygenation and increase the work of breathing.

Diaphragm Dysfunction

Diaphragm dysfunction may be the major contributor to reductions in lung volumes noted after abdominal and thoracic procedures. The precise mechanisms that underlie diaphragm dysfunction are not fully understood. Some evidence implicates a decrease in central nervous system output to the phrenic nerves that may be due to inhibitory reflexes triggered by sympathetic, vagal, or splanchnic receptors in the chest or abdominal cavities.

Impaired Gas Exchange Manifested by Hypoxemia

In the first twenty-four hours after surgery, hypoxemia is largely related to the residual effects of the anesthesia (alveolar hypoventilation, ventilation-perfusion mismatch, anesthetic-induced inhibition of hypoxic pulmonary vasoconstriction, right-to-left shunting, and depressed cardiac output).

Following thoracic and abdominal surgeries, hypoxemia is also due to processes that include decreased lung volumes (particularly FRC); alveolar hypoventilation induced by narcotic analgesics; increased dead space ventilation caused by rapid, shallow breathing; and decreased mixed venous oxygen tension that is due to increased oxygen consumption and decreased oxygen delivery from anemia and impaired cardiac output.

Respiratory Depression

In the early postoperative period, the residual effects of pre-anesthetic or anesthetic agents inhibit respiratory drive and ventilatory responses to hypoxia, hypercapnia, and acidemia. Subsequently, narcotics administered for postoperative pain depress both hypoxic and hypercapnic ventilatory responses, thereby decreasing minute ventilation and increasing PaCO2. In addition, narcotics reduce or even completely suppress sighs, and they precipitate sleep apnea in susceptible patients.

Impairment of Lung Defense Mechanisms (Cough and Mucociliary Transport)

Pain, muscle weakness, and excessive use of narcotics may suppress cough. An ineffective cough, atelectasis, presence of an endotracheal tube, and inhalation of anesthetic or dry, hyperoxic gas mixtures (which damage the cilia) act in concert to impair mucocillary clearance.

Which individuals are at greatest risk of developing a postoperative pulmonary complication?

Risk factors that predict the development of postoperative pulmonary complications have traditionally been divided into patient-related risk factors and procedural-related risk factors.

Patient-related risk factors include the following:

  • Age

  • Chronic lung disease

  • Cigarette use

  • Congestive heart failure

  • Functional dependence

  • American Society of Anesthesiologists (ASA) classification

  • Obstructive sleep apnea

  • Pulmonary hypertension

  • Metabolic and nutritional factors

Some of these risk factors merit discussion below.

Age: The risk of postoperative pulmonary complications increases continuously for all individuals older than 50. An American College of Physicians (ACCP) systematic review found that the odds ratio (OR) for postoperative pulmonary complications for individuals age 50 to 59 years, 60 to 69 years, 70 to 79 years, and > 79 years was 1.5, 2.3, 3.9, and 5.6, respectively.

Chronic lung disease: Chronic obstructive pulmonary disease (COPD) has consistently been identified as a strong risk factor for the development of postoperative pulmonary complications. Cumulative risk, however, does not continuously increase as the severity of the obstruction measured via forced vital capacity in 1 second (FEV1) increases for nonthoracic surgery.

Cigarette use: Smoking, independent of its association with COPD, is an important risk factor for the development of postoperative pulmonary complications. Smoking cessation for 8 weeks or more prior to surgery is associated with a statistically significant reduction in postoperative respiratory complications. Concerns (based on retrospective studies) that stopping smoking for a shorter period of time before surgery paradoxically increases the risk of complications have not been confirmed by prospective studies.

Functional dependence: The OR for postoperative pulmonary complications in patients with total dependence, defined as the inability to perform any activities of daily living independently, was found in the ACCP systematic review to be 2.5. Partial dependence, defined as the ability to perform some but not all of the activities of daily living independently, conferred an OR of 1.6.

American Society of Anesthesiologists (ASA) classification: The ASA classification system is one of the strongest predictors of the development of postoperative pulmonary complications. When an individual with an ASA class of II or greater is compared to an ASA class of I, the OR for the development of postoperative pulmonary complications was found to be 4.9.

Obstructive sleep apnea: A meta-analysis of 13 studies identified that in patients with OSA the OR for the development of respiratory failure and hypoxemia postoperatively were 2.4 and 2.3, respectively, as compared to patients without the diagnosis.

Pulmonary hypertension: Patients with pulmonary hypertension are especially at risk for the development of many postoperative complications, including pulmonary and nonpulmonary ones.

Metabolic and nutritional factors: Patients with an albumin of less than 3.6 g/dL demonstrate increased risk of postoperative pulmonary complications.

Well-controlled asthma and obesity, in the absence of concomitant OSA, are not risk factors for postoperative pulmonary complications.

Procedural-related risk factors for postoperative pulmonary complications include the following :

  • Prolonged surgery (>3 hours)

  • Surgical site

  • General anesthesia

  • Neuromuscular blockade agent used

  • Intraoperative ventilatory strategy

  • Emergent surgery

Some of these risk factors merit additional discussion below.

Surgical site: Thoracic and surgical procedures involving the upper abdomen demonstrate an increased risk of postoperative pulmonary complications. Vascular, neurological, and head and neck surgeries also are associated with increased risk.

Neuromuscular blockade agent used: Pancuronium, a long-acting neuromuscular blocking agent, is associated with increased risk of postoperative pulmonary complications compared to other neuromuscular blocking agents with shorter duration. The etiology is presumed to be due to residual partial muscular paralysis at the time of emergence from anesthesia.

Intraoperative ventilatory strategy: A meta-analysis of 15 randomized controlled trials demonstrated that the use of low tidal volume ventilation, defined as less than 8mL/kg of ideal body weight, reduced postoperative pulmonary complications in all patients from 14.7% to 8.7% compared to conventional intraoperative mechanical ventilation.

Multiple models have been validated to estimate an individual’s risk of postoperative pulmonary complications.

The Arozullah respiratory failure index and Arozullah pneumonia risk in the postoperative period on noncardiac surgery index were the first indices to help clinicians quantify a patient’s risk for respiratory failure and pneumonia, respectively. Most of the criteria used in the indices are risk factors discussed above. Calculators using the criteria are freely available online. Because these indices were derived from a database of patients in the Veterans Affairs (VA) Hospital system of which approximately 85% of the sample population was male, the external validity of these calculators is a point of criticism.

More recently two new indices, the Gupta calculator for respiratory failure and the Gupta calculator for postoperative pneumonia derived from a large (>200,000 patients) American College of Surgeons’ National Quality Improvement data set, were created. The patient population that comprised the data set contained a more heterogenous population of patients and thus the external validity is believed to be greater than the Arozullah indices. The respiratory failure index takes into account the procedure type, ASA class, if the surgical procedural will be performed emergently, the functional status of the patient, and the presence of preoperative sepsis. These calculators are also freely available online to assist clinicians in quantifying an individual’s risk of postoperative pulmonary failure and/or pneumonia.

What laboratory studies should you order to help make the diagnosis, and how should you interpret the results?

A preoperative albumin may help in assessment of a patient’s risk of postoperative pulmonary complications as described above.

Arterial blood gas analysis is not routinely indicated to assist with the preoperative pulmonary assessment, but may provide guidance in the postoperative setting in advanced lung disease.

What imaging studies will be helpful in making or excluding the diagnosis of a postoperative pulmonary complication?

Indications for a preoperative chest x-ray include new or unexplained respiratory symptoms or signs. A meta-analysis evaluating the utility of obtaining routine preoperative chest X-rays revealed that only 0.1% of routine preoperative chest X-rays influenced management. Routine chest X-rays are thus not recommended in the absence of new respiratory signs or symptoms for patients undergoing noncardiothoracic surgery.

What non-invasive pulmonary diagnostic studies will be helpful in making or excluding the diagnosis of a postoperative pulmonary complication?

Routine preoperative pulmonary function testing for noncardiothoracic surgery is not indicated .

Spirometry is indicated in a patient with unexplained respiratory signs and symptoms such as dyspnea and cough as it may diagnose the patient with an underlying chronic lung disease such as COPD. This diagnosis helps to appropriately risk stratify the patient since COPD is a risk factor for postoperative pulmonary complications as described above. Furthermore, it assists the clinicians in risk mitigation for postoperative pulmonary complications, as the patient can then be prescribed appropriate bronchodilator therapy for the patient’s COPD stage prior to surgery.

If you decide the patient has a postoperative pulmonary complication, how should the patient be managed?

Evidence-based risk mitigation and management strategies for patients assessed to be at risk for postoperative pulmonary complications are divided into preoperative interventions, intraoperative interventions, and postoperative interventions.

Preoperative Interventions

  • Optimization of lung function in patients with COPD using bronchodilator therapy: In patients with COPD, the regular use of appropriate bronchodilator therapy for a patient’s COPD stage or the availability of as needed bronchodilator therapy reduces complications in patients with COPD compared to patients with COPD who do not use bronchodilator therapy in non-thoracic surgery. In patients with an acute exacerbation of asthma or COPD, surgery should be delayed until the patient has appropriately recovered due to increased rates of exacerbation when surgery is performed when active symptoms are present.

  • Smoking cessation ideally for at least 8 weeks prior to surgery: Smoking cessation less than 8 weeks prior to surgery does not increase perioperative pulmonary complications.

  • Education: Preoperative education on proper lung expanding maneuver technique may reduce perioperative pulmonary complications compared to waiting until after surgery.

Intraoperative Interventions

  • Limit surgical duration to less than 3 hours where appropriate.

  • Avoid the use of the long-acting neuromuscular blocking agent pancuronium when possible.

  • Limit tidal volume delivered during anesthesia while on mechanical ventilation to less than 8mL/kg ideal body weight.

Postoperative Interventions

  • Use of lung expanding maneuvers: Deep breathing, incentive spirometry, chest physical therapy, ambulation, intermittent positive-pressure breathing, and continuous positive pressure breathing are all various lung expanding maneuvers that have been evaluated in the postoperative setting to reduce postoperative pulmonary complications. In general, no single modality is superior to others for routine use after nonthoracic surgery to reduce pulmonary complications. Although incentive spirometry and deep breathing exercises, which are the most well studied and least labor intensive, do reduce postoperative pulmonary complications , the greatest benefit for these interventions may be for patients at high risk for pulmonary complications after surgery.

Early patient mobilization and ambulation

  • Adequate analgesia: In many postoperative situations, patient-controlled analgesia, epidural analgesia, and intercostal nerve blocks provide more effective pain control than parenteral narcotics do.

  • Selective use of a nasogastric tube: Routine placement and use of a nasogastric tube after abdominal surgery is associated with more postoperative pulmonary complications than selective use only in patients who require gastric decompression. Routine placement is not recommended.

  • Prophylaxis for thromboembolism

  • Special considerations in patients with OSA: Patients with OSA are particularly prone to all types of postoperative pulmonary complications. Strategies related to analgesia, oxygenation, patient positioning, and monitoring may be effective in reducing complications. Limiting the use of opioids, especially parenteral opioids, with the use of nonsteroidal anti-inflammatory agents, regional analgesia, and neuraxial opioids, is recommended. The use of continuous positive airway pressure (CPAP), ideally with the patient’s home device, is recommended for all patients with OSA and if hypoxemia is present in the postoperative period. Patients with OSA should be placed in nonsupine positions during the recovery period if possible and all patients with OSA should have continuous pulse oximetry monitoring in the immediate postoperative period.

Specific management of patients who experience atelectasis, respiratory infection, exacerbation of an underlying lung disease, respiratory failure, need for prolonged mechanical ventilation, or pulmonary embolism after surgery should be managed as described elsewhere.

What is the prognosis for patients managed in the recommended ways?

Individual elements of the approach outlined above have been demonstrated effective in reducing the risk of postoperative pulmonary complications. The approach, including all its elements, is likely to prevent or limit the development of respiratory complications after surgery. A multidisciplinary approach in the postoperative setting using many of the interventions listed above to reduce pulmonary complications was recently evaluated and found to be effective. The ICOUGH trial, an acronym for the individual components of the approach consisting of incentive spirometry, cough and deep breathing exercises, oral care, understanding (patient education), getting out of bed three times daily, and head-of-bed elevation, reduced postoperative pulmonary complications from 2.6% to 1.6%.

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