Adult Chest Surgery

Chapter 4. Preoperative Evaluation

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.

PATIENT POPULATION UNDERGOING THORACIC SURGERY

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. 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 for cigarette smoke exposure.1,2

Several reports use the Charlson Comorbidity Index as an indicator of comorbid conditions and predictor of postoperative complications. This index generates a score based on the presence of comorbid conditions and has been demonstrated to stratify the risk of postoperative complications in thoracic surgery patients.3,4 In a recent study, the mean age of patients undergoing esophagectomy was 58.1 years, with 45% of patients over age 60.In another study from Japan, the median age was 62.3 years, and 88% were male.A recent study comparing transhiatal esophagectomy with transthoracic esophagectomy reported mean ages of 69 and 64 years, with patients up to age 79 included in the study.In a recent review, 28–32% of patients undergoing esophagectomy in the United States were over age 75, and 40% had a Charlson score greater than 3.8

Similarly, patients with lung cancer tend to be older and to have multiple comorbid conditions. In a series of 344 patients, 36% were over age 70, and 95% had a significant smoking history.A recent review of Medicare patients undergoing thoracic surgery in the United States showed that in patients undergoing lobectomy, 32–35% were over age 75 (44% women), and 32% had a Charlson score greater than 3.In the same series, 21–26% of patients undergoing pneumonectomy were over age 75 (28% women), and 56% had a Charlson score greater than 3.

Thus the patient population presenting for major thoracic surgical procedures tends to be older, has a high incidence of comorbid conditions, and contains a disproportionate number of patients with obstructive lung disease. 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?"10

PHYSIOLOGIC EFFECTS OF THORACIC SURGERY

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.11

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.12–14 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 infectious complications. The closing volume is elevated in patients with underlying lung disease, narrowing the distinction between the FRC and 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.

MOST COMMON COMPLICATIONS AFTER THORACIC SURGERY

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.9,15,16 It follows, therefore, that particular attention to pulmonary and cardiac reserve and risk factors should be a major component of the preoperative evaluation.

GOALS OF 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 AND PHYSICAL EXAMINATION

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. It is well established that there is a broad range of symptoms and functional impairments in patients with similar pulmonary function test results.17 As described below, functional capacity is a major determinant of operative candidacy, and it is often up to the evaluating clinician to supplement objective testing data with a subjective assessment of the patient's capacity to determine the likelihood of perioperative morbidity/mortality.

Table 4-1 highlights the important components of the patient history. Although age is a risk factor for perioperative morbidity, much of this added risk is a consequence of the accompanying comorbidities. In the absence of comorbid conditions, age alone only modestly increases the perioperative risk and usually should not be viewed as the sole contraindication to surgery, although it is often a factor used by both patient and physician to assess the risk and potential benefit of surgery.18–21 While many of the elements of the history are self-explanatory, several bear further exposition. A critical component of the preoperative evaluation is the assessment of the patient's functional status. Functional status is 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 (discussed below).

Table 4-1. Important Components of the History in Preoperative Evaluation

·   Presenting symptoms and/or circumstances of diagnosis

·   Prior diagnosis of pulmonary or cardiac disease

·   Comorbid conditions: diabetes mellitus, liver disease, renal disease

·   Prior experiences with general anesthesia and surgery

·   Cigarette smoking: never, current, ex-smoker (If ex-smoker, when did patient stop?)

·   Inventory of functional capacity of patient

·   Medications/allergies

·   Alcohol use, including prior history of withdrawal syndromes

 

 

In addition to these functional considerations, patients should be asked about signs or symptoms that may suggest the presence of metastatic disease. These include new onset of headaches, focal neurologic signs or symptoms, new onset of a seizure disorder, bone pain, or recent fractures. Patients also should be questioned for symptoms related to paraneoplastic syndromes, which can range from relatively subtle symptoms of hypercalcemia to more dramatic neurologic symptoms.

At this time, it is appropriate to advise any patient who still smokes cigarettes to quit; under ideal circumstances, patients should stop 6–8 weeks before elective surgery to permit resolution of pulmonary inflammation resulting from smoke exposure. Pharmacotherapy improves the likelihood of successful abstinence.22 Currently available pharmacotherapies include nicotine, bupropion, and most recently, varenicline.

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's syndrome in patients with a lung mass. Any noted abnormalities, such as asymmetric pupils, should be carefully recorded to avoid confusion concerning whether it is a postoperative development. The pulmonary examination should include an assessment of diaphragmatic motion (by percussion) and note of any paradoxical respiratory pattern in the recumbent position. The relative duration of exhalation, as well as the presence or absence of wheezing, should be noted. 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.

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.16,23

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. For patients undergoing pulmonary parenchymal resection, review of images is essential to estimate the amount of lung that will be removed in surgery. In this setting, patients usually have a computed tomography (CT) of the chest. In addition to the pathology for which the patient has been referred, the scan should be reviewed for the presence of signs of emphysema or pulmonary fibrosis. In general, review of imaging is an important component of surgical planning and determination of the extent of resection, which, in turn, influences the process of patient evaluation.

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, pleural biopsy, or esophageal surgery 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(DLCO). 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 values for FEV1 and DLCO (ppo-FEV1 and ppo-DLCO, respectively).

PREDICTION OF POSTOPERATIVE LUNG FUNCTION

Predicted postoperative 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.24 The two common approaches for calculating postoperative lung function are simple calculation and regional assessment of lung function.

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 = FEV1[1 – (number of segments resected x 0.0526)]. The calculation is similar for DLCO. 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.

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 ventilation/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 predicted postoperative value. Using the quantitative / data, the ppo-FEV1 or ppo-DLCO is calculated as follows: ppo value = baseline value x (100 – percent ventilation or perfusion in the region of planned resection)/100.

Table 4-2. Indications for Preoperative Assessment of the Regional Distribution of Lung Function

·   Significant airflow obstruction on spirometry (FEV1 <65% of predicted and FEV1/FVC <0.70)

·   Significant pleural disease

·   Known or suspected endobronchial obstruction

·   Central lung mass

·   History of prior lung resection

·   Presence of lobar collapse or major atelectasis on imaging

 

 

FVC, forced vital capacity.

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. While 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-riskpatients have prohibitive risk. For further refinement of risk in this group, an assessment of functional capacity needs to be obtained.

Table 4-3. Risk Assessment for Pulmonary Surgery

Higher Risk

Lower Risk

Age >70

FEV1 >2 L for pneumonectomy; >1 L for lobectomy; >0.6 L for segmentectomy

Higher extent of resection

Predicted postoperative FEV1 >30–40% of predicted (pneumonectomy > lobectomy > wedge resection)

Poor exercise performance

Stair climbing >5 flights for pneumonectomy; 3 flights for lobectomy

Low predicted postoperative FEV1

Cycle ergometry >83 W

Low predicted postoperative DLCO

Predicted postoperative DLCO >40% of predicted

High PCO2 (controversial)

Maximal oxygen uptake >15–20 mL/kg/min

 

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, a test of performance is indicated. Although most references suggest that abnormal pulmonary function is defined as an FEV1 or DLCO of less than 60% of predicted, the only prospectively validated algorithm uses the more conservative value of less than 80% of predicted for both these parameters.

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, with one recent report suggesting that patients able to climb three flights of stairs (54 steps) have adequate reserve for lobectomy and approximately five flights for a pneumonectomy.9,25–28

More recently, much of the literature has focused on the use of incremental cardiopulmonary exercise testing, with expired gas analysis, to quantify cardiopulmonary reserve. Such testing, which can be performed with either a treadmill or cycle ergometer, 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. Some reports suggest that the latter is more appropriate for stratifying patient risk.29 Studies using this approach have established that patients with an MVO2of greater than 15–20 mL/kg/min have an acceptable risk for pulmonary resection.30–32 Conversely, patients with an MVO2 of less than 10 mL/kg/min have a high risk of perioperative mortality.33–35

Most recently, reports have used the predicted postoperative exercise capacity (ppo-MVO2) as a predictor of postoperative risk.33 This value is calculated using the results of both the cardiopulmonary exercise test 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.

Not surprisingly, in addition to being predictive of mortality, functional capacity is also predictive of perioperative complications and hospital length of stay.36

There is no consensus as to the sequence of testing one should follow in evaluating patients for thoracic surgery. The American Thoracic Society and European Respiratory Society have published guidelines for preoperative evaluation of patients with COPD that recommend several approaches to this situation (Figs. 4-1 and 4-2). 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.37 In practice, the particular sequence used often depends on local practice and the availability of testing, particularly cardiopulmonary testing. A typical sequence of evaluation is the history, physical examination, screening spirometry, and initial blood tests. For patients with significant airflow obstruction on spirometry or those who report substantial functional impairment, further evaluation is indicated. Quantitative / scanning allows calculation of ppo-FEV1; patients with a ppo-FEV1 or ppo-DLCO of less than 40% of predicted should have a performance test of functional capacity. Alternatively, such patients could first undergo a test of functional capacity, followed when indicated by a quantitative / scan.

Figure 4-1.

 

Prospectively validated approach to preoperative evaluation. (From ATS/ERS Guidelines.37 )

 

Figure 4-2.

 

Simplified alternative approach to preoperative evaluation. (From ATS/ERS Guidelines.37 )

CARDIAC ASSESSMENT

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. 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 (cardiac risk >5%, operations with an anticipated long procedure time, major fluid shifts and/or blood loss) or intermediate-risk (1% > cardiac risk <5%, intrathoracic surgery) categories.

The cornerstone of preoperative cardiac evaluation is a careful history and physical examination. In addition to inquiries directed at cardiac risk factors, such as family history, smoking history, history of hypercholesterolemia, history of diabetes mellitus or hypertension, and history of prior cardiac disease, special attention should be directed to questions that elicit the patient's functional capacity.

Clinical predictors of increased perioperative cardiovascular risk are stratified into three classes.

·   Major. Unstable coronary syndromes, including recent myocardial infarction (defined as <30 days), unstable or severe angina, decompensated congestive heart failure, severe valvular disease, and significantarrhythmias, including high-degree atrioventricular block, symptomatic ventricular arrhythmias in the setting of underlying heart disease, or supraventricular arrhythmias with an uncontrolled ventricular response.

·   Intermediate. Mild angina, prior myocardial infarction or electrocardiographic evidence of same, compensated or history of prior heart failure, diabetes mellitus, and renal insufficiency.

·   Minor. Advanced age, abnormal electrocardiogram, rhythm other than sinus, low functional capacity, history of stroke, and uncontrolled systemic hypertension.

The combination of the classification of clinical predictors, the patient's functional capacity, and the risk of surgery then determine the approach to preoperative evaluation. Current guidelines recommend a stepwise approach to the evaluation after a comprehensive history, physical examination, and review of the electrocardiogram. If a patient has had coronary revascularization within the past 5 years and has not had a clinical change since then, or if the patient has had a cardiac evaluation within the past 2 years that did not demonstrate the patient to be at high risk, further testing usually is not indicated. If neither of these considerations applies, the next step is to classify patients according to their clinical predictors.

For patients with major clinical predictors, delay of the procedure should be considered for all but emergency procedures. Such patients should have medical risk-factor management and modification initiated, and consideration should be given to performing coronary angiography.

For patients with intermediate clinical predictors who have either a poor functional capacity or are contemplating a high-risk procedure, noninvasive testing should be performed. Should such testing demonstrate high risk factors, coronary angiography should be considered. If noninvasive testing indicates a low risk, the patient may proceed to surgery. Patients with moderate or excellent functional capacity who are scheduled for intermediate- or low-risk surgical procedures may proceed with surgery without further evaluation.

Patients with minor or no clinical predictors and low functional capacity considering a high-risk surgical procedure should undergo noninvasive testing followed by consideration of coronary angiography for patients with results indicating high risk. In others with minor or no clinical predictors scheduled for procedures of lesser risk and in patients with moderate or excellent functional capacity, no further preoperative evaluation is needed.

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 instituted when the patient is stable enough to tolerate the proposed treatment.

SUMMARY

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 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 6–8 weeks before surgery.22

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.16,38

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