4: Preoperative Evaluation of Thoracic Surgery Patient

The decision to proceed with any surgical procedure involves a careful consideration of the anticipated benefits of surgery and an assessment of the risks associated with the operation. An important component of estimating the benefit of surgery is knowledge of the natural history of the condition in question. It is a popular, though inaccurate, conception of the preoperative evaluation that the evaluating physician “clears” the patient for surgery. This implies a binary clinical scenario: Either the patient is at low risk and is “cleared” or the risk is excessive and the patient is “turned down” for surgery. The reality, of course, is more complex and often more gray than black and white. A more accurate view of preoperative evaluation fulfills two goals: first, to accurately define the morbidity and risks of surgery, both short and long term, and second, to identify specific factors or conditions that can be addressed preoperatively to modify the patient's risk of morbidity. The formulation of an approach to accomplish these goals requires knowledge of both the specific characteristics of the patient population and the general effects of thoracic surgery on patients.

Many patients undergoing a noncardiac thoracic surgical procedure do so as a consequence of known or suspected lung or esophageal cancer. These diseases share the common risk factor of a significant and prolonged exposure to cigarette smoking and commonly include older individuals. The combination of age and prolonged cigarette smoking yields a population with a significant incidence of comorbid factors beyond the primary diagnosis. A major source of comorbidity in the population of patients with lung cancer is the presence of chronic obstructive pulmonary disease (COPD). The diagnosis of COPD is an independent risk factor for the development of lung cancer, after controlling cigarette smoke exposure.^1,2 The combination of these factors, plus the magnitude of the surgical procedures, presents a challenge to the clinicians evaluating such patients. The potential for perioperative morbidity and mortality is substantial, but at the same time, the lack of effective alternative therapy for the patient's malignancy means that the consequence of not being a surgical candidate is almost certain death. This quandary led Gass and Olsen to ask, “What is an acceptable surgical mortality in a disease with 100% mortality?”³

The Charlson Comorbidity Index (CCI),⁴ which generates a score based on the presence of comorbid conditions, was originally designed as a measure of the risk of 1-year mortality attributable to comorbidity of hospitalized patients. This index has been demonstrated to stratify the risk of postoperative complications in thoracic surgery patients.^4,5 In nonsmall cell lung cancer patients, the CCI is a better predictor of survival than individual comorbid conditions and has been recommended for use in the selection of patients for NSCLC surgery.⁶ A recent study, compared the CCI to another comorbidity index, the Kaplan–Feinstein index (KFI), and demonstrated the CCI performed better at predicting perioperative mortality and death from noncancer causes after surgery.⁷

Surgical procedures and the anesthesia administered to permit such procedures have significant impact on respiratory physiology that contributes to the development of postoperative pulmonary complications. Because the incidence of pulmonary complications is directly related to the proximity of the planned procedure to the diaphragms, patients undergoing pulmonary, esophageal, or other thoracic surgical procedures fall into the category of patients at high risk for postoperative respiratory complications.⁸

Intraoperatively, the use of inhaled volatile agents can affect gas exchange by altering diaphragmatic and chest wall function. These changes occur without corresponding alterations in blood flow and give rise to areas of low ventilation/perfusion and cause the gradient for alveolar–arterial oxygen to widen.

In the postoperative period, a number of factors contribute to the development of complications. These include an alteration in breathing pattern to one of rapid shallow breaths with the absence of periodic deep breaths (sighs) and abnormal diaphragmatic function. These breathing derangements are caused by pain and diaphragmatic dysfunction secondary to splanchnic efferent neural impulses arising from the manipulation of abdominal contents. This has the effect of reducing the functional residual capacity (FRC), that is, the resting volume of the respiratory system. The FRC declines by an average of 35% after thoracotomy and lung resection and by approximately 30% after upper abdominal operations.⁹ If the FRC declines sufficiently to approach closing volume—the volume at which small airways closure begins to occur—patients may develop atelectasis and are predisposed to impairment in gas exchange and infectious complications.¹⁰ The closing volume is elevated in patients with underlying lung disease, narrowing the distinction between the FRC and the closing volume.

The alterations in lung volume that occur as a result of reduction in both the inspiratory capacity (the maximal inhalation volume attained starting from a given lung volume) and the expiratory reserve volume (the maximal exhalation volume from a given lung volume) contribute to a decline in the effectiveness of cough and cause increased difficulty in clearing pulmonary secretions.

The complications associated with thoracic procedures are reviewed in Chapter 8 and are discussed with greater specificity in the many surgical technique chapters of this book. In general, however, the most common complications after major thoracic procedures are respiratory and cardiovascular. Although the exact frequency varies from series to series, pneumonia, atelectasis, arrhythmias (particularly atrial fibrillation), and congestive heart failure are the most common. Myocardial infarction, prolonged air leak, empyema, and bronchopleural fistula, although less common, also occur with significant frequency.¹¹ It follows, therefore, that particular attention to pulmonary and cardiac reserve and risk factors should be a major component of the preoperative evaluation.

The clinicians evaluating a patient for a major thoracic surgical procedure have several goals for the evaluation process. The foremost objective is to provide an accurate assessment of the short- and long-term risks of morbidity and mortality for a given procedure in a given patient while identifying factors that can be addressed preoperatively to reduce the possibility of adverse events. Less obvious benefits of the comprehensive evaluation include identification of risk factors and other health issues that may facilitate institution of interventions regardless of the plans for surgery.

History

Although the field of thoracic surgery has been dramatically altered by the development of new technologies, both in imaging and in therapeutics, the history and physical examination remain the most important components of the preoperative evaluation. There is no substitute for a careful history and physical examination when it is performed by an experienced clinician. Table 4-1 highlights the important components of the patient history. Although age is a risk factor for perioperative morbidity and often a factor used by both patient and physician to assess the risk and potential benefit of surgery,^12-15 much of this added risk is a consequence of the accompanying comorbidities. Recent publications suggest age alone is not an independent factor predicting mortality. Chambers et al.¹⁶ showed that 30-day mortality rates, hospital length of stay, and global quality of life (QoL) were not influenced by age (age <70 years vs. age ≥70 years). Similar findings were found by Okami et al.,¹⁷ who reported that octogenarian patients with stage I lung cancer had reasonable long-term outcomes.

Although many of the elements of the history are self-explanatory, several bear further exposition.

Patients who are current smokers should be advised to quit. Importantly, there is a better chance of achieving smoking cessation in COPD patients after a lung cancer diagnosis (over 50%)¹⁸ compared with smokers without this diagnosis, and better survival has been reported for those who quit after a diagnosis of early-stage lung cancer versus those who continue to smoke.¹⁹ In addition, smokers compared with nonsmokers are at greater risk of postoperative complications including delayed wound healing, pulmonary and cardiovascular complications, and mortality as shown in randomized trials.²⁰ A meta-analysis found a relative risk reduction of 41% for prevention of postoperative complications with trials of 4 weeks smoking cessation having the largest treatment effect.²⁰ The ideal time for quitting is still controversial. A small number of observational studies have described a paradoxical increase in the risk of postoperative complications in patients who quit within 2 months of surgery,²¹ which may be related to a selection bias (sicker subjects at increased risk of complications were more likely to quit).²⁰ A large retrospective study of in-hospital outcomes for 7990 primary lung cancer resections found an increased mortality for current smokers with adjusted odd ratio (AOR) 3.5 and confidence intervals (CIs) 1.1 to 11 and for those who quit for less than a month prior to surgery (AOR: 4.6, CI: 1.2–18).²² However, there was no difference in mortality between current smokers and those who quit within a month. Therefore, it is recommended that patients be advised to quit smoking before surgery regardless of the time and, if possible, allow for a month of smoking abstinence to reduce the risk of postoperative complications to the level of a nonsmoker.²³

Pharmacotherapy improves the likelihood of successful abstinence. Combining the use of nicotine replacement therapy and counseling has a higher rate of success.²⁴ Currently available pharmacotherapies include nicotine replacement therapy, bupropion, and nicotine agonist, varenicline.²⁴

A critical component of the preoperative evaluation is the assessment of the patient's functional status. It is well established that there is a broad range of symptoms and functional impairments in patients with similar pulmonary function test results.²⁵ As described below, functional capacity is a major determinant of operative candidacy and an important component of the decision algorithm for both the pulmonary and cardiac elements of the preoperative evaluation. A number of approaches have been taken to determine functional capacity. These include questionnaires, tests of locomotion (e.g., the 6-minute walk or stair climbing tests), and cardiopulmonary exercise testing (CPET) (discussed below).

Physical Examination

Although most patients being evaluated for thoracic surgery have a normal or near-normal physical examination, it is an important component of the evaluation. The examination of the patient should include an assessment of general overall appearance, including signs of wasting. Respiratory rate and the use of accessory muscles of respiration should be noted. Careful observation of the patient as he or she moves around the examining room, climbs onto the examination table, lies down, and sits up can provide important information about functional status. Examination of the head and neck should include assessment of adenopathy and focal neurologic deficits or signs, particularly Horner syndrome in patients with a Pancoast tumor. The pulmonary examination should include an assessment of diaphragmatic motion (by percussion) and note of any paradoxical respiratory pattern in the recumbent position. The presence of rales should raise the possibility of pneumonia, heart failure, or pulmonary fibrosis. The cardiac examination should include assessment of a third heart sound to suggest left ventricular failure, murmurs to suggest valvular lesions, and an accentuated pulmonic component of the second heart sound to suggest pulmonary hypertension. The heart rhythm and the absence or presence of any irregular heartbeats should be noted. The abdominal examination should note liver size, presence or absence of palpable masses or adenopathy, and any tenderness. The examination of the extremities should note any edema, cyanosis, or clubbing. The presence of clubbing should not be attributed to COPD and raises the possibility of intrathoracic malignancy or congenital heart disease. The patient's gait should be observed both as an assessment of neurologic function and to confirm the patient's ability to participate in postoperative mobilization.

Pulmonary rehabilitation improves exercise capacity in patients with moderate and severe COPD. This intervention can improve the exercise performance in patients with severely reduced exercise capacity (<10 mL/kg/min or nonsurgical candidates) to a potentially resectable level (mean improvement 2.8 mL/kg/min).²⁶ However, the recommended duration of these programs (6–8 weeks) restricts the implementation of this intervention in the great majority of cases. Although there is evidence that the length of hospital stay could be shortened by 3 days with this intervention,²⁷ there is scarce information of other beneficial effects. Therefore, the use of pulmonary rehabilitation before surgical treatment for lung cancer may have a role limited to those patients with much reduced exercise capacity and early-stage lung cancer.

Laboratory Studies

It is a reasonable practice to check electrolytes, renal function, and clotting parameters and to order a complete blood count as part of the preoperative assessment. In patients with known or suspected malignancy, liver function tests and serum calcium also should be checked. Arterial blood gases may have a role in documenting a patient's baseline for future comparison, but the previously held view that resting hypercarbia (elevated Pco₂) in isolation is a contraindication to thoracic surgery is no longer valid.²⁸

Imaging Studies

The options for radiologic imaging are reviewed in Chapter 3 and are covered with specificity in the surgical technique chapters of this text.

Pulmonary Function Testing

The utility of preoperative pulmonary function testing in part depends on the type of operative procedure being planned. Preoperative pulmonary function testing is unlikely to contribute to the preoperative evaluation of patients undergoing mediastinoscopy, drainage of pleural effusions, or pleural biopsy when there is no prior history of lung disease or unexplained dyspnea. For patients who report dyspnea, significant functional limitation, prior pulmonary resection, or a diagnosis of COPD with a recent change in functional capacity; however, pulmonary function testing is an appropriate component of the evaluation.

Preoperative pulmonary function testing is mandatory for patients who are being considered for pulmonary parenchymal resection. Although a number of pulmonary function tests have been examined in this setting, two have emerged with predictive value for postoperative complications. These are the forced expiratory volume in 1 second (FEV₁) measured during spirometry and the diffusing capacity of the lung for carbon monoxide (D_LCO). Either of these values can be used to provide an estimate of the risk of operative morbidity and mortality. In addition, they are used to calculate the predicted postoperative (ppo) values for FEV₁ and D_LCO (ppo-FEV₁ and ppo-D_LCO, respectively).²⁹

Prediction of Postoperative Lung Function

The ppo lung function has been demonstrated to be an important predictor of operative risk. In general, the available methods for calculating postoperative lung function underestimate actual measured lung function once the patient has recovered from surgery.²⁹ The two common approaches for calculating postoperative lung function are simple calculation (recommended for lobectomies) and regional assessment of lung function (recommended for pneumonectomy).³⁰

Simple calculation is based on the assumption that the patient's lung function is homogeneously distributed. The calculation requires knowledge of the number of segments to be resected and the preoperative value. For FEV₁, the formula is ppo-FEV₁ = preoperative FEV₁ × (1 - (number of unobstructed segments to be resected/total number of unobstructed segments)). The calculation is similar for D_LCO. For most patients, this simple approach to calculation is sufficient and, as mentioned earlier, results in a conservative prediction of pulmonary function after recovery from surgery. Traditionally, a ppo-FEV₁ or D_LCO of 40% or lower was used to categorize a patient as a high risk for lung surgery. However, advances in perioperative management and surgical techniques (concomitant lung volume reduction and minimally invasive surgery) have further reduced the lower ppo limit to 30% in selected cases.²⁹ For patients with ppo-FEV₁ or ppo-D_LCO values <40%, the predicted postoperative product (PPP) may be used (where PPP = ppo-FEV₁ × ppo-D_LCO). Patients with PPP<1650 have been shown to have a high risk of operative mortality.³¹

In certain situations, simple calculation does not predict postoperative lung function accurately. The clinical situations for which regional assessment of lung function is indicated are summarized in Table 4-2. A number of approaches have been used to attempt to assess the regional distribution of lung function, including lateral position testing, bronchospirometry, quantitative radionuclide ventilation/perfusion scanning, and quantitative CT scanning. Although quantitative CT scanning holds promise in this regard, the current standard test is radionuclide scanning. Typically, the data from quantitative radionuclide perfusion scans are reported as the percent function contributed by the six lung regions: upper third, middle third, and lower third of each hemithorax. These data, combined with the preoperative lung function value and the location and planned extent of surgical resection, permit a calculation to be made of the ppo value. Using the quantitative V̇/Q̇ data, the ppo-FEV₁ or ppo-D_LCO is calculated as ppo value = baseline value × (100 – percent perfusion in the region of planned resection)/100.

Assessment of Functional Capacity

In many ways, assessment of functional capacity is the most critical component of the preoperative assessment in patients considering thoracic surgery. It is a decisive factor for determining whether further cardiac evaluation is needed (as outlined below) and is the major factor for determining the operative suitability of patients with significant impairment of lung function. As outlined at the beginning of this chapter, such patients are “overrepresented” in this population by virtue of the additional independent risk engendered by obstructive lung disease. As outlined in Table 4-3, there are reasonable guidelines for identifying patients at low risk for morbidity and mortality after thoracic surgery. Although lung function and calculation of anticipated postoperative function can fairly reliably identify patients at low risk, these factors do less well at defining which high-risk patients have prohibitive risk. For further refinement of risk in this group, an assessment of functional capacity needs to be obtained.

Although the clinician can derive an assessment of functional capacity based on the initial history and physical examination, for patients whose history suggests significant functional impairment or who have abnormal pulmonary function tests (FEV₁ or D_LCO <80% predicted), a test of performance is indicated.

Performance Tests of Functional Capacity

Historically, clinicians have used tests of ambulation as a semiquantitative assessment of functional capacity. Early teaching in the field used stair climbing as a measure of functional reserve, establishing a threshold of performance that connotes acceptable risk. This test has held up remarkably well over time. Patients able to climb three flights of stairs (54 steps) have adequate reserve for lobectomy and approximately five flights for a pneumonectomy.^11,32,33 A recent report of 640 patients who underwent lobectomy or pneumonectomy confirmed the utility of stair climbing in assessing postoperative risk; they observed a significant decrease in the risk of postoperative complications and mortality in the group of patients who climbed 22 m or more (110 steps) compared with those who climbed 12 m (approximately 60 steps in the United States).³⁴

More recently, much of the literature has focused on the use of incremental CPET, with expired gas analysis, to quantify cardiopulmonary reserve. Such testing that can be performed with either a treadmill or cycle ergometer (preferred method) allows quantification of maximal exercise capacity, expressed as maximal oxygen uptake rate (MVo₂). This can be expressed as an absolute value in units of milliliters of O₂ per kilogram of body mass per minute or as a percent of predicted. Studies using this approach have established that patients with an MVo₂ of greater than 15 to 20 mL/kg/min have an acceptable risk for pulmonary resection.^29,30 Conversely, patients with an MVo₂ of less than 10 mL/kg/min have a high risk of postoperative complications and perioperative mortality.²⁹

Most recently, reports have used the ppo exercise capacity (ppo-MVo₂) as a predictor of postoperative risk. This value is calculated using the results of both the CPET and quantitative lung function testing in a manner analogous to that used to calculate ppo-FEV₁. A ppo-MVo₂ of less than 10 mL/kg or 35% predicted is associated with a high postoperative mortality.²⁹

Not surprisingly, in addition to being predictive of mortality, functional capacity is also predictive of perioperative complications and hospital length of stay.³⁵

There is no consensus as to the sequence of testing one should follow in evaluating patients for thoracic surgery. The American Thoracic Society (ATS),³⁶ American College of Chest Physicians (ACCP),³⁰ and European Respiratory Society/European Society of Thoracic Surgery²⁹ have published guidelines for preoperative evaluation of patients with COPD that recommend several approaches to this situation. They differ primarily in respect to whether exercise testing or quantitative lung function assessment is the first test performed in patients with abnormal lung function and/or a history suggestive of a low functional capacity. The ATS has published a validated algorithm that incorporate these concepts (Fig. 4-1) and a second more simplified algorithm that includes stair climbing as the measure of functional capacity (Fig. 4-2). We acknowledge that the particular sequence used often depends on local practice and the availability of testing, particularly CPET. A typical sequence of evaluation is the history, physical examination, screening spirometry, and initial blood tests. For patients with airflow obstruction on spirometry and/or reduced diffusion capacity or those who report substantial functional impairment, further evaluation with a CPET is indicated.²⁹ According to the exercise capacity level, estimation of the ppo lung function by simple calculation or perfusion scintigraphy is indicated. Alternatively, lung function testing and ppo lung function calculation could be estimated first, followed by a CPET when indicated.

The basic philosophy of cardiac assessment for surgical procedures has changed in recent years, as reflected in the recent guidelines jointly formulated by the American College of Cardiology and the American Heart Association.³⁷ The preoperative evaluation is now viewed as an opportunity to perform a general cardiac assessment and to initiate risk-factor modification/management rather than a specific intervention centered on surgery. The practice is to institute medical management as indicated by the patient's condition rather than specific preoperative recommendations. As a consequence, coronary revascularization, either by catheter approach or via bypass grafting, is rarely indicated solely to reduce operative risk in a particular patient.

The preoperative cardiac evaluation incorporates consideration of both the cardiac risks associated with the operation under consideration and the specific risk factors of the patient under consideration. In general, thoracic surgical procedures fall into the high risk (i.e., patients with >5% cardiac risk, and operations associated with a lengthy anticipated procedure time, major fluid shifts and/or major blood loss) or intermediate risk (i.e., cardiac risk >1% but <5%) categories.

The cornerstone of preoperative cardiac evaluation is a careful history and physical examination. As previously highlighted, in addition to inquiries directed at cardiac risk factors, special attention should be directed to questions that elicit the patient's functional capacity. The functional capacity is measured as metabolic equivalents (METs). Patients unable to meet a four METs demand during activities of daily living (walk four blocks or climb two flights of stairs) have an increased perioperative cardiac and long-term risk. As discussed earlier in the chapter, patients undergoing surgery for pulmonary neoplasm have a high incidence of prior tobacco use, which is associated with an increased risk for lung cancer, COPD, and coronary arterial disease (CAD). In addition, assessment of CAD is more difficult among these patients because limitations in exercise tolerance can be due to either CAD, lung disease, or both. It is wise to have a higher index of suspicion of comorbid CAD in patients undergoing intrathoracic surgery.

In the 2002 ACC/AHA guidelines, the committee chose to segregate clinical risk factors into major, intermediate, and minor risk factors. The 2007 guidelines modified this classification.³⁷ The updated guidelines continue to identify a set of active cardiac conditions, of which, the presence of one or more of these conditions mandates intensive management and may result in delay or cancellation of surgery unless the surgery is emergent. These conditions include unstable coronary syndromes defined as unstable or severe angina and recent (<30 days) MI, decompensated heart failure, significant arrhythmias, and severe valvular disease.

However, the intermediate-risk category has been replaced with the set of clinical risk factors that comprise the Revised Cardiac Risk Index, derived and validated for the prediction of cardiac risk for stable patients undergoing nonurgent major noncardiac surgery.³⁸ These factors include history of ischemic heart disease, mild angina, history of compensated or prior heart failure, history of cerebrovascular disease, diabetes mellitus, and renal insufficiency.

Minor risk factors remain the same; recognized markers for cardiovascular disease that do not independently predict increased perioperative risk; advanced age (>70 years), abnormal ECG (LV hypertrophy, left bundle branch block, ST-T abnormalities), rhythm other than sinus, and uncontrolled systemic hypertension.

The revised guidelines recommend a stepwise approach to the evaluation after a comprehensive history, physical examination, and review of the electrocardiogram.

For all patients, any long-term issues meriting consideration of risk-factor modification and/or therapy should be addressed in the postoperative period and appropriate therapy should be instituted when the patient is stable enough to tolerate the proposed treatment.

The cornerstone for evaluating any patient under consideration for a thoracic procedure is a well-performed history and physical examination. For patients considering major thoracic procedures, this often should be supplemented by screening pulmonary function testing. Subsequent evaluation will be dictated by the results of this initial process. For patients with significant functional impairment or abnormal testing, estimation of postoperative function should be performed and consideration should be given to a formal test of functional capacity. Previously held concepts that advanced age and resting hypercarbia are absolute contraindications to surgery are no longer valid. Any patient who is an active smoker at the time of evaluation should be instructed to quit and offered pharmacotherapeutic assistance; ideally, this should be done at least 4 weeks before surgery.

A common clinical scenario begins with review by the evaluating physician of imaging studies, prior test results, screening spirometry, and perhaps a letter from a referring physician. Armed with this information, the clinician then enters the examination room and interviews and examines the patient. In this scenario, clinicians often state that a patient looks “better” or “worse” than expected based on the previously available information. This clinical impression is often supported by the results of functional capacity assessment; patients who “look better” than expected often have a functional capacity that permits major surgery with relatively low postoperative mortality.^28,39

We wish to acknowledge Dr. John J. Reilly for his contribution to prior versions of this chapter.