14 - Laboratory Investigations in the Diagnosis of Pulmonary Diseases

Editors: Shields, Thomas W.; LoCicero, Joseph; Ponn, Ronald B.; Rusch, Valerie W.

Title: General Thoracic Surgery, 6th Edition

Copyright 2005 Lippincott Williams & Wilkins

> Table of Contents > Volume I - The Lung, Pleura, Diaphragm, and Chest Wall > Section V - Assessment of the Thoracic Surgical Patient > Chapter 19 - Pulmonary Physiologic Assessment of Operative Risk

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Chapter 19

Pulmonary Physiologic Assessment of Operative Risk

Mark K. Ferguson

Complications occur frequently after major thoracic surgery. Their development is related to a variety of factors, including the type of operation performed, the approach to the operation, and the underlying condition of the patient. The occurrence of pulmonary and cardiovascular complications is associated with prolonged hospitalization, a higher cost of hospital care, and an increase in operative mortality. Every effort should be made to reduce the incidence of such complications and to manage them expeditiously when they occur.

The ability to predict which patients are at higher risk for postoperative complications enables physicians and other caregivers to select appropriate patients for major surgery and to discuss relative risks with patients so that informed consent about a planned operation can be obtained. Risk stratification may identify patients who might benefit from preoperative cardiopulmonary rehabilitation in an effort to reduce the incidence of complications and may direct patients to physicians or medical centers better able to manage higher-risk operations. Risk stratification also permits comparison of outcomes among physicians and medical centers for quality-improvement purposes.

The development of pulmonary and cardiovascular complications, as well as the risk for operative mortality after pulmonary, esophageal, and upper abdominal operations, has been shown to be associated with the preoperative pulmonary status of the patient. Ensuring that an appropriate pulmonary physiologic assessment of patients has been performed before their operations is the responsibility of the treating surgeon. Historically, surgeons have been among the leaders in developing criteria for risk stratification based on pulmonary physiologic status. These efforts have led to valuable algorithms, enabling treating physicians to quantify the relative risk for complications based on a few important tests. However, mere numbers should not be used to make recommendations for individual patients; clinical judgment is still the most important factor in the successful surgical care of patients.

HISTORICAL BACKGROUND

The relationship of pulmonary function to mortality was first suggested by Hutchinson (1846), the inventor of the spirometer, who was the first person to describe the vital capacity of the lungs. He demonstrated the linear relationship of vital capacity to height and the lack of a relationship between vital capacity and weight for a given height. After nearly a century of work by a large number of investigators, lung volume measurements and terminology were codified by Christie (1932), who also described a reliable technique for measuring functional residual capacity. Gaensler (1951) was among the first to describe the utility of timed volume measurements in the assessment of pulmonary insufficiency. Gaensler and associates (1955) also identified the utility of routine pulmonary function testing in assessing risk for operative mortality and long-term morbidity after lung resection. Subsequent large-scale studies, such as those of Kannel (1980) and Schunenmann (2000) and their colleagues, have demonstrated the relationship between vital capacity and mortality in the general population, echoing the work of Hutchinson nearly a century and a half earlier.

EFFECTS OF SURGERY ON PULMONARY FUNCTION

The type of operation and the incision used to perform an operation have varying deleterious effects on pulmonary function that have been well described with regard to the extent of functional decrement and the time course of recovery. Functional residual capacity (FRC) has been recognized for decades as the single most important lung volume measurement associated with the development of pulmonary complications after most types of operations. FRC is the lung volume that exists at the end of normal expiration; its components are the expiratory reserve volume and the

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residual volume (Fig. 19-1). A number of factors are associated with a postoperative decrease in FRC, including general anesthesia, conditions that increase intraabdominal pressure such as obesity and ascites, the supine position, and, most important, the type and location of incisions used for an operation.

Fig. 19-1. Lung volume measurements and their interrelationships. TLC, total lung capacity; VC, vital capacity; RV, residual volume; IC, inspiratory capacity; FRC, functional residual capacity; IRV, inspiratory reserve volume; TV, tidal volume; ERV, expiratory reserve volume; RV, residual volume.

FRC is important in part because of its interaction with the closing volume (CV) of the lung. The CV is the volume of the lung at which airflow from dependent parts of the lung stops during expiration owing to airway closure. Factors that promote an increase in CV include advancing age, tobacco use, fluid overload, bronchospasm, and the presence of airway secretions. Under normal circumstances, FRC is about 50% and CV is about 30% of total lung capacity. A reduction in FRC or an increase in CV results in premature airway closure and atelectasis, as first suggested by Alexander and coauthors (1971, 1972). The resulting ventilation-perfusion mismatch causes hypoxia, and trapping of secretions contributes to pneumonitis, both of which may contribute to the development of respiratory insufficiency.

No consistent changes in FRC occur after operations that do not involve the abdomen or thorax. In contrast, FRC decreases by 10% to 15% after lower abdominal operations, upper abdominal operations cause a decrease in FRC of 30%, and thoracotomies result in a 35% decrease in FRC. The reduction of FRC after abdominal surgery is attributed to both dysfunction of abdominal wall musculature and impaired diaphragm function. Open upper abdominal incisions were shown by Ford and colleagues (1983) to cause a substantial decrease in diaphragm and lung function. Open operations cause greater perturbations in lung function than do laparoscopic operations, as reported by Chumillas (1998), Karayiannakis (1996), and Schauer (1993) and their associates, although adverse effects after laparoscopic operations are nevertheless substantial according to the study of Williams and colleagues (1993). Sharma and coauthors (1999) demonstrated that maximum diaphragmatic pressure decreases after laparoscopic upper abdominal procedures by more than 50% during the first 6 hours after surgery. Partial recovery was evident 24 hours after surgery. Similar reductions were identified by Erice and colleagues (1993). They and Joris and associates (1997) also found minimal reductions in diaphragmatic activity and lung function after laparoscopic lower abdominal procedures compared with those evident after upper abdominal laparoscopy, demonstrating that even minimally invasive procedures cause diaphragmatic and ventilatory dysfunction that is dependent on the location of the operation.

Simmoneau and colleagues (1983) opine that postoperative pain is not an adequate explanation for these changes, which develop despite adequate postoperative analgesia. Diaphragmatic contractility is not altered after upper abdominal operations. Instead, it has been suggested by Dureuil and co-workers (1986) that reflexes inhibit phrenic nerve output. Extradural block has been shown by the studies of Manikian (1988) and Pansard (1993) and their associates to improve postoperative diaphragmatic function after upper abdominal surgery, supporting the contention that interruption of afferents that inhibit diaphragm activity may result in improved outcomes.

The performance of a sternotomy has deleterious effects on chest wall mechanics and postoperative pulmonary function, possibly leading to pulmonary complications. A restrictive pattern was shown by van Belle and co-workers (1992) to develop in the early postoperative period that was manifested by a decrease in FRC and impaired inspiratory and expiratory pressures. Respiratory pressures returned to normal 6 weeks postoperatively, but FRC and other ventilatory parameters remained decreased. Locke and colleagues (1990) also demonstrated the presence of a restrictive ventilatory defect in the early postoperative period after median sternotomy owing to reduced and uncoordinated rib cage expansion, but these findings did not persist when the patients were tested 3 months postoperatively. Harvesting an internal mammary artery graft for coronary revascularization was shown by Berrizbeitia and coauthors (1989) to impair chest wall mechanics more than when saphenous vein grafts were used. Overall, the reports suggest that structural alterations in chest wall mechanics and decreased blood flow to intercostal muscles are responsible for restrictive ventilatory changes after sternotomy that may be related to the development of pulmonary complications.

Thoracotomy is the operative approach associated with the highest potential risk for postoperative pulmonary complications

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owing to restricted chest wall motion, impaired diaphragm activity, and possible loss of pulmonary parenchyma. The development of diaphragmatic dysfunction after thoracotomy has been shown by Fratacci and associates (1993) to resemble the dysfunction that accompanies upper abdominal operations. The same authors demonstrated that epidural analgesia does not reverse diaphragmatic dysfunction after thoracotomy, a situation analogous to upper abdominal surgery. A thoracotomy incision transiently reduces most ventilatory parameters postoperatively, with a precipitous drop occurring by the first postoperative day (Fig. 19-2). At the end of the second postoperative week, some recovery occurs, but the deleterious effects do not resolve for almost 3 months after surgery. The studies of Furrer (1997), Nagahiro (2001), and Nakata (2000) and their colleagues have shown that thoracoscopic operations cause a somewhat smaller decrement in pulmonary function during the immediate postoperative period. The advantage persists for the first postoperative week, after which both open thoracotomy and thoracoscopic approaches to major lung resection appear to have similar outcomes. Major lung resection permanently reduces spirometric values and diffusing capacity by varying degrees, depending on the amount of lung that is resected. When measured 6 months to 1 year postoperatively, segmental or wedge resections reduce lung function by less than 10%, lobectomy or bilobectomy results in decreases of 5% to 15%, and pneumonectomy reduces values by 20% to 40% (Fig. 19-3).

Fig. 19-2. Changes in forced vital capacity (FVC) and in the forced expiratory volume in 1 sec (FEV₁) during the first 3 months after thoracotomy. Data from Berend et al. (1980), Furrer et al. (1997), Giudicelli et al. (1994), Hazelrigg et al. (1991), Lemmer et al. (1990), Markos et al. (1989), Nakata et al. (2000), and Nomori et al. (1997).

Fig. 19-3. Permanent changes inforced vital capacity (FVC), forced expiratory volume in 1 sec (FEV₁), and diffusing capacity of lung for carbon monoxide (D_lco) after various types of lung resection. Data from Ali et al. (1980), Begin et al. (1984), Bolliger et al. (1996), Bria et al. (1983), Foroulis et al. (2002), Miyazawa, et al. (1999), Nezu et al. (1998), Nishimura et al. (1993), Nugent et al. (1999), Pierce (1993), Santambrogio et al. (2001), Takizawa et al. (1999), van Mieghem and Demedts (1989), Williams et al. (1984), and Zeiher et al. (1995).

PREDICTIVE FACTORS FOR POSTOPERATIVE PULMONARY MORBIDITY AND MORTALITY

Most of this chapter deals with the assessment of patients who are candidates for major lung resection, including lobectomy, bilobectomy, and pneumonectomy. Many useful data have been generated regarding factors that are associated with postoperative morbidity for these operations (Table 19-1). As a result, a variety of algorithms have been suggested for preoperative assessment of such patients, and these are discussed in detail later in this chapter. In contrast,

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the relationships among preoperative physiologic tests and postoperative morbidity and mortality have been difficult to establish for nonpulmonary operations. As a result, information about the utility of physiologic assessment of other general thoracic surgical patients is scant and is discussed at the end of the chapter.

Table 19-1. Tests of Cardiopulmonary Physiologic Status and the Factors They Assess

Test	Units	Lung Capacity	Airway Resistance	Gas Exchange	Muscle Strength	Cardiac Output	Effort and Motivation
FVC	L
FEV1	L
FEV1/FVC
MVV	L/min
Dlco	mL/min/mm Hg
Vo2max	mL/kg/min
FVC, forced vital capacity; FEV1: forced expiratory volume in 1 second; MVV, maximum voluntary ventilation; Dlco, diffusing capacity of lung for carbon monoxide; Vo2max; maximum oxygen consumption during exercise.

Lung Volume Measurements

The measurement of lung volumes, including total lung capacity (TLC) and residual volume (RV), is useful in the evaluation of the lung resection candidate. Vital capacity is decreased when TLC is reduced by restrictive processes, when RV is increased owing to air trapping in obstructive disease, or by a combination of these factors (Fig. 19-4). Recognition of which elements contribute to a decreased vital capacity may help in assessing the preoperative patient. This distinction is not possible to make without measurement of RV, which cannot be obtained by routine spirometry, but requires helium equilibration, nitrogen washout, or body plethysmography techniques to determine.

Restrictive physiology causes reductions in vital capacity as well as TLC, RV, and FRC. It is caused by pulmonary fibrosis, sarcoidosis, muscular weakness and disease, chest wall deformities, large acquired diaphragmatic hernia, and trapped lung owing to extensive pleural fibrosis. In the case of a trapped lung, surgery that includes a pulmonary decortication may help resolve the restrictive physiology, resulting in improved pulmonary dynamics postoperatively. Similar effects are produced by surgical correction of a large diaphragmatic hernia. None of the other conditions that cause a restrictive physiology are improved by thoracic surgery, highlighting the possible risk to these patients of major thoracic surgical procedures.

Obstructive physiology causes reductions in vital capacity, but there are associated increases in TLC, RV, and FRC. It is usually caused by emphysema, chronic bronchitis, and asthma. The use of bronchodilators and, in severe cases, inhaled or systemic steroids can dramatically improve obstructive physiology in patients with reactive airways disease, making thoracic surgery much safer. In highly selected patients with heterogeneous emphysema, resection of the most affected regions of the lung can result in an increase in VC. In most other instances, the abnormal measurements are relatively fixed, and majorlung surgery further reduces vital capacity.

Fig. 19-4. Relative changes in lung volumes associated with lung diseases (see Fig. 19.1 for definitions).

Spirometry

The relationship between vital capacity and mortality in the general population was identified in the mid-1800s. By the middle of the 20th century, a variety of lung volume measurements were being used in the physiologic assessment of lung resection candidates. Cournand and Richards (1941) were among the first to describe the lack of association between dyspnea and vital capacity; they noted that maximum breathing capacity was correlated with respiratory insufficiency. Additional important studies on maximum breathing capacity were performed by Gilson and Hugh-Jones (1949), who demonstrated greater perturbations in maximum breathing capacity than in vital capacity in patients with pneumoconiosis. Many authors, including Gaensler (1951), Birath and Crafoord (1951), and Woodruff and co-workers (1953), ultimately recognized the lack of clinical utility of measurement of vital capacity alone in predicting which patients will do well after thoracic surgery.

Gaensler (1951) first described the utility of timed volume measurements in assessing pulmonary sufficiency for surgery. This work demonstrated that timed measurements, such as maximum breathing capacity (now known as maximum voluntary ventilation, or MVV) and the forced expiratory volume in 1 second (FEV₁), were more sensitive in assessing pulmonary sufficiency than was vital capacity. The report showed that reductions in vital capacity correlated with restrictive ventilatory defects, whereas decreases in MVV and FEV₁ correlated with obstructive ventilatory abnormalities. The use of MVV as an aide in decision making for thoracic surgery was well summarized by Woodruff and colleagues (1953) based on experience with lung resection at Saranac Lake. The publication of Gaensler and associates in 1955 subsequently confirmed the clinical impression that operative mortality and long-term postoperative respiratory insufficiency generally were related to vital capacity, with mortality occurring primarily in patients with vital capacity less than 60% to 70% of predicted. They also found that mortality was more clearly related to abnormalities of timed measurements such as MVV and FEV₁, demonstrating that most operative and long-term deaths due to respiratory insufficiency occurred in patients with an MVV of less than 50% of predicted.

Mittman (1961) confirmed the utility of MVV as an indicator of increased risk in patients undergoing thoracic surgery and also suggested the use of MVV of less than 50% of predicted as a threshold for determining which patients

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were at high risk. Boushy and coauthors (1971) were among the first to describe FEV₁as the best predictor of which patients would not tolerate major lung resection, suggesting that an FEV₁of less than 2.0 L put patients into a high-risk group, particularly patients older than 60 years of age. Lockwood (1973) subsequently described patients at increased risk as having an FEV₁ of less than 1.64 L and those at very high risk for major lung resection as having an FEV₁of less than 1.20 L. He also identified patients at increased risk as having an MVV of less than 52 L/min and those at very high risk as having an MVV of less than 28 L/min. Olsen and coauthors (1975) confirmed the general guidelines of FEV₁of less than 2.0 L and MVV of less than 50% of predicted as indicative of a potential increased risk for major lung surgery and suggested that additional physiologic studies be obtained in patients at increased risk. During the 1960s and 1970s, the use of timed measurements of expiratory volumes thus became standard in the evaluation of lung resection candidates.

Predicted Postoperative Function

The utility of predicted postoperative function as a determinant of operability was recognized in the 1940s and 1950s. The original techniques used for calculating predicted postoperative function included bronchospirometry, unilateral pulmonary artery occlusion, and the lateral position test. Neuhaus and Cherniak (1968) used bronchospirometry that was performed by intubating patients (while awake) with a double-lumen endotracheal tube and connecting each lumen of the tube to separate spirometers. In this way, the relative contribution of each lung to vital capacity could be measured, and the contribution of each lung to MVV could be calculated. Assessment of predicted postoperative function after pneumonectomy was thus possible. An alternative to this was unilateral pulmonary artery occlusion by a balloon-tipped catheter floated into the pulmonary artery through a transvenous route. The balloon was filled with radiopaque fluid so that its position could be established with fluoroscopy. Once occlusion was accomplished, hemodynamic measurements, including pulmonary artery pressure and oxygen saturation, were taken. The relationship between body position and individual lung function was described in the 1950s, and the clinical utility of measurement of lung function with patients in the lateral position, known as the lateral position test, was reported by Bergan in 1960. This technique provided results similar to bronchospirometry while avoiding the need for cumbersome equipment and considerable patient discomfort. All of these tests are now of historical interest because of the introduction of lung scintigraphy.

Pulmonary scintigraphy was initially developed in the 1950s to study the regional distribution of lung ventilation using a number of radiolabeled gases. In the 1960s, the technique was expanded to enable study of regional lung perfusion using radiolabeled gases as well as radiolabeled microaggregates of human serum albumin. A clinically useful technique for studying regional lung ventilation and perfusion using xenon 133 (¹³³Xe) was described by Ball and others in 1962. Unsuspected abnormalities in regional perfusion associated with centrally located tumors were sporadically reported in the late 1950s and early 1960s. Miorner (1968) described the similarities between differential lung function measurements made by bronchospirometry and radiospirometry and suggested the routine use of quantitative pulmonary scintigraphy in patients determined to be at increased risk for major lung resection on the basis of a decreased MVV.

The utility of lung scintigraphy in estimating postoperative function was first reported in 1972 by Kristersson and colleagues. The technique was found by Ali (1975) and Olsen (1975) and their associates to be particularly useful for patients undergoing pneumonectomy. The percentage of function attributed to the lung not being resected was multiplied by the preoperative measured value of lung function to achieve a predicted postoperative value for lung function (Fig. 19-5). Ali and associates (1980) subsequently developed a technique for using lung scintigraphy to estimate postoperative function in patients undergoing lobectomy. They calculated the expected loss of function by multiplying the preoperative FEV₁ by the percentage of function to the affected lung and by the percentage of segments of that lung that were to be resected.

The superiority of perfusion over either ventilation alone or a combination of ventilation and perfusion for estimating postoperative lung function was demonstrated by Wernly and coauthors (1980). The percentage of perfusion to the lung not being resected was multiplied by the preoperative spirometric value to estimate the resultant postoperative value. The correlation between calculated and actual measurements of postoperative lung function was high, and the error rate was less than 10% (Fig. 19-6). This finding has been confirmed by other centers, including the observations of Sangalli and colleagues (1992). They suggested that patients who are candidates for pneumonectomy but who have a preoperative FEV₁ of less than 2.0 L should undergo

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quantitative radionuclide lung perfusion scanning to assess relative distribution of function between the two lungs.

Fig. 19-5. Quantitative perfusion scan (anterior view) of a patient with a proximal right upper lobe lung cancer. Distribution of radiotracer is indicated according to upper and lower lung zones.

Fig. 19-6. Comparison of calculated and measured postoperative forced expiratory volume in 1 second (FEV₁) for patients after lobectomy (left, 63 patients) and pneumonectomy (right, 45 patients). The solid lines were calculated by linear regression, and the dashed lines represent the lines of identity. Data from Bolliger et al. (2002), Sangalli et al. (1992), Wernly (1980), and Williams et al. (1984).

Pulmonary scintigraphy as a means for estimating postoperative pulmonary function yielded specific cutoff values for operability that differed among investigators. Kristersson and coauthors (1972) believed that a postoperative predicted FEV₁ of less than 1 L precludes resection, whereas Olsen and colleagues (1975) suggested that a cutoff value for FEV₁ of 0.8 L should be used. The latter group based their recommendations on the incidence of hypercapnia in unoperated patients with an FEV₁ of less than 0.8 L reported by Segall and Butterworth in 1966. Despite the lack of conclusive evidence supporting this guideline, a postoperative predicted FEV₁ of between 800 mL and 1 L is still used by many surgeons as a guideline for distinguishing between normal-risk and high-risk candidates for major lung resection.

The calculation of postoperative lung function using simple equations rather than physiologic tests was originally introduced by Juhl and Frost (1975), who assigned an equal value to each of the 19 lung segments in order to determine the amount of functioning lung remaining after resection. The preoperative spirometric value was multiplied by the percentage of lung segments remaining after resection, resulting in a predicted postoperative value. This concept was explored in further detail by Wernly and associates (1980). Despite the fact that all segments were used in the calculation of predicted postoperative values for FEV₁ regardless of their functional status, the correlation between the predicted and actual postoperative values for FEV₁ was high, and the error range was only 7%. Using this technique, an increase in postoperative morbidity was demonstrated in patients with a predicted postoperative FEV₁ of less than 1 L by Kearney and co-workers (1994) or less than 900 mL as noted by Putnam and colleagues (1990). A number of authors, such as Sangalli (1992), Williams (1984), and Zeiher (1995) and their co-workers, have confirmed the good correlation between predicted postoperative and measured postoperative FEV₁ and FVC in patients undergoing major lung resection. However, postoperative predicted values after resection can underestimate or overestimate FEV₁ by an average of 250 mL. Part of the explanation for the discrepancy between predicted and measured values in some studies might have been the inclusion of nonfunctioning segments in the estimation of postoperative function, as suggested by Zoia and associates (1998).

More recent techniques, as reported by Egeblad and collaborators (1986), for calculating predicted postoperative spirometric values use the number of functioning segments as the denominator and the number of functioning segments to be resected as the numerator for purposes of calculating predicted postoperative values. In this way, segments that are nonfunctional (owing to obstruction by a proximal cancer or consolidation or destruction due to an inflammatory process) are not included in the calculation:

According to Bolliger and associates (2002), this calculation technique is superior to the use of all lung segments regardless of functional status. A refinement of the anatomic technique for estimating postoperative function was proposed by Nakahara and colleagues (1985), who described the use of the proportion of 42 functioning subsegments planned for resection as the basis for calculating predicted postoperative function. Bolliger and associates (2002) believe that this technique offers little advantage over the use of functional segments in estimating postoperative pulmonary

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function. The use of quantitative computed tomography (CT) in estimating relative lung function as a means for calculating predicted postoperative function has been shown by Bolliger (2002) and Wu (2002) and their colleagues to be similar to lung perfusion scintigraphy in the accuracy of predicting postoperative function. In general, quantitative CT or scintigraphic assessment of perfusion is similar to anatomic techniques for estimating postoperative function after segmentectomy or lobectomy, whereas anatomic techniques are not as accurate for estimating postoperative function after pneumonectomy.

Spirometry Expressed as a Percentage of Predicted Normal Values

Despite the apparent utility of preoperative and predicted postoperative FVC and FEV₁ in assessing a patient's risk for major lung resection, these absolute rather than relative criteria did not allow for the known variation of lung function related to sex, age, and height. Normal spirometric values based on age, sex, and body height were published as early as 1948 by Baldwin and associates (1948), and reference values currently are readily available according to Hankinson and co-workers (1999). Gass and Olsen (1986) illustrated the problem of using absolute rather than relative criteria for predicting risk, stating that a postoperative FEV₁ of 800 mL represented 48% of the predicted normal for a short, elderly woman but only 21% of the predicted normal for a tall, middle-aged man. Kohman and colleagues (1986) demonstrated a significant increase in pulmonary complications among patients with a preoperative FEV₁ of less than 67% of predicted. Subsequent work reported by Dales and co-workers (1993) suggested that a preoperative FEV₁ of less than 60% of predicted was associated with a 2.5-fold increase in the incidence of pulmonary complications after lung resection, and Sekine and collaborators (2002) noted that a preoperative FEV₁ of less than 70% of predicted also was associated with a significant increase in the risk for pulmonary complications. In contrast, according to Santambrogio and associates (2001), a cutoff value of FEV₁ of less than 80% of predicted does not appear to select patients who are at increased risk for pulmonary complications or death after lung resection. Pate and coauthors (1996) suggested the use of FEV₁ of less than 40% of predicted as a limit for safe major lung resection.

Taking the next logical step by combining the concepts of spirometry expressed as a percentage of predicted and calculation of predicted postoperative spirometric values, Gass and Olsen (1986) theorized that a calculated postoperative value of 30% of predicted might be a useful guideline for identifying patients at high risk for major lung resection, which was close to the value of 33% identified by Ali and coauthors (1983) as a suitable cutoff. The cutoff value of 30% of normal for a predicted postoperative FEV₁ was also suggested by Nakahara and co-workers (1988) for determining excess risk based on a retrospective clinical study. Other authors have suggested a postoperative predicted value for FEV₁ of 40% of normal as a means for selecting patients who are at high risk for lung resection. Markos and associates (1989) described a 50% mortality rate among patients with a postoperative predicted FEV₁ of less than 40% of normal after lung resection, whereas patients with a postoperative predicted FEV₁% of more than 40% suffered no operative mortality. Pierce and colleagues (1994) described a fourfold increase in operative mortality using a postoperative predicted FEV₁ of less than 40% of normal to separate risk groups. Schuurmans and coauthors (2002) supported the use of a postoperative predicted FEV₁ of less than 40% for identifying patients who are at increased risk for major lung resection. Putnam and colleagues (1990) demonstrated that a predicted postoperative FEV₁ of less than 34% of normal was predictive of increased operative mortality after pneumonectomy.

Diffusing Capacity of the Lung

It is logical that reduced diffusing capacity of the lung for carbon monoxide (D_LCO) is associated with pulmonary morbidity and operative mortality after major lung resection. Diffusing capacity is a measurement of the gas exchange function of the lung at the alveolar capillary interface. It usually is measured by a single breath technique as originally described by Ogilvie and associates (1957). The most important factor determining D_LCO is the volume and surface area of the capillary bed in contact with alveolar gas. Loss of alveolar surface resulting in a reduced D_LCO is most commonly seen in emphysema, but other factors that obliterate capillaries, such as vasculitis, embolic disease, and inflammatory interstitial diseases, may also decrease diffusing capacity. Processes that reduce gas entry, such as filling of alveoli and ventilation maldistributions, also result in a reduced D_LCO. Low hemoglobin may cause a decrease in gas uptake, whereas congestive heart failure with an associated increase in hemoglobin may cause an increase in gas uptake; these factors can theoretically influence D_LCO, but they usually are corrected for in calculating the D_LCO. Patients with lung cancer were shown by Barreto and coauthors (1993) to have a decreased D_LCO out of proportion to their degree of emphysema based on spirometric studies, suggesting the presence of subclinical emphysematous changes not detectable by routine spirometry.

A substantial decrease in D_LCO was shown by Bates and colleagues (1956) to be associated with a substantial decrease in long-term survival in patients with emphysema. Acute decreases in D_LCO were documented by McIlroy and Bates (1956), as well as by Curtis (1958) and Burrows (1960) and their associates, to occur after lung resection. Boushy and associates (1970) demonstrated an important relationship between low diffusing capacity and operative

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mortality after major lung resection. Dietiker and coauthors (1960) demonstrated chronic decreases in D_LCO to occur after lung resection, averaging 20% for wedge resection, 30% for lobectomy, and 41% for pneumonectomy. A similar decrease in D_LCO after lobectomy was reported by Berend and co-workers (1980). Cander (1963) recommended the routine assessment of D_LCO in patients who were candidates for major lung resection. In general, diffusing capacity does not decrease chronically after pneumonectomy to the same extent that spirometric values do, and patients appear to tolerate exercise better than would be expected. Hsia and associates (1992) suggested that this might be due to the normal ability to recruit D_LCO during exercise that is preserved even after pneumonectomy.

The author and associates (1988) identified D_LCO as an independent predictor of postoperative pulmonary complications and mortality after major lung resection. They suggested that a preoperative D_LCO of less than 60% of predicted is an indicator of high risk for postoperative complications. In contrast, Wang and colleagues (2000) suggested that the cutoff value for increased risk should be 70% of predicted. Markos and associates (1989) described increased accuracy in predicting postoperative respiratory complications and mortality using the predicted postoperative D_LCO expressed as a percentage of normal, suggesting patients with a predicted postoperative D_LCO of less than 40% of predicted were at excessive risk. This value was confirmed by the author and co-workers (1995) (Fig. 19-7). A low diffusing capacity has been shown by Bousamra and associates (1996) to predict not only postoperative complications but also the likelihood of long-term oxygen use and readmission for respiratory problems during the first year after major lung resection. However, Wang and colleagues (1999a) demonstrated that long-term survival has been demonstrated to be unrelated to the predicted postoperative diffusing capacity.

Fig. 19-7. The relationship between diffusing capacity, age, and mortality after major lung resection. Data from Ferguson et al. (1995).

Exercise Capacity and Oxygen Consumption

Decreased exercise capacity after major lung resection was recognized in the 1940s and 1950s in the investigations of Cournand and Berry (1942) as well as those of Lester (1942), Cournand (1947), Harrison (1958), and Burrows (1960) and their associates. The degree of dysfunction was correlated with advanced patient age, reduced MVV, and increased RV. Reduced exercise capacity was also associated with the degree of pulmonary arterial hypertension that developed during exercise.

The etiology of decreased exercise tolerance after major lung resection is multifactorial. As the amount of resected lung increases, the lung becomes stiffer, and elastic recoil pressure similarly rises. The work of breathing thus increases, as noted by Baarends and co-workers (1997), requiring shunting of blood from working extremity muscles to muscles doing the work of breathing. Maximum effort tolerance decreases, which, according to van Miegham and Demedts (1989), is associated with an increase in pulmonary artery pressure and pulmonary vascular resistance during exercise compared with preoperative values. Similarly, peripheral vascular resistance and peripheral arterial blood pressure increase during exercise, changes that are associated with a decrease in cardiac output and stroke volume. Arterial oxygen saturation decreases during exercise, possibly owing to a lower diffusing capacity as suggested by Hsia (1992) and Mossberg (1976) and their colleagues. The changes are most pronounced after pneumonectomy, but proportionally smaller changes are evident after lobectomy as recorded by Brunelli (2001), Nezu, (1998), and Nugent (1999) and their co-workers. Interestingly, Bolliger and associates (1996) recorded that ventilatory impairment does not limit exercise tolerance in most situations. Exercise training in patients who have undergone major lung resection according to the studies of Hijazi and colleagues (1998) results in an increase in maximum oxygen consumption, endurance, and peripheral oxygen extraction. However, in comparison to normal people who undergo exercise training, no increase in cardiac and stroke indexes occur. The irreversibly fixed stroke index and a reduced area of gas exchange in the lung are believed by DeGraff (1965) and Hsia (1992) and their co-workers to be the major sources of exercise limitation in patients after major lung resection.

The rationale for preoperative exercise testing is to permit identification of patients who are close to the margin of cardiopulmonary function so that the risks of surgery and the status of postoperative exercise tolerance can be predicted. Exercise testing quantifies what many believe to be the best determinant of functional capacity: oxygen consumption

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during maximum exercise, or Vo₂max. The potential advantage of exercise testing over conventional tests, such as spirometry and measurement of diffusing capacity, is that most components that determine performance are evaluated, including ventilatory function, gas exchange, cardiac function, cardiopulmonary conditioning, and effort. The disadvantages of exercise testing include the need for costly resources to perform the technically demanding versions of the test, the lack of validation of the unsophisticated versions of the test, and the need for considerable patient effort and cooperation in order to achieve reliable results.

One form of exercise testing that was introduced early in clinical practice was verification that patients were able to complete a fixed exercise challenge to enable them to qualify for major lung resection. Tasks included such things as ascending a specified number of steps or flights of stairs and walking for 6 minutes to enable measurement of the distance covered. These types of evaluation are currently used frequently and are clinically valuable. They enable some quantitation of effort but do not permit assessment of the underlying cause for an inadequate performance. A second form of assessment of cardiopulmonary function is submaximal exercise testing, as was suggested by Olsen and associates (1989). This requires invasive monitoring of respiratory gas exchange and pulmonary hemodynamics during exercise. This technique was used sporadically in the early decades of major lung resection but is no longer in routine clinical use. The most common technique of exercise testing involves the assessment of physiologic parameters, particularly oxygen consumption, during maximum exercise (Vo₂max). This requires measurement of oxygen uptake, carbon dioxide output, minute ventilation, blood pressure, electrocardiogram, and pulse oximetry. Patients undergo symptom-limited incremental exercise on a cycle ergometer or on a treadmill. Weisman (2001) opines that Vo₂max is generally considered the best indicator of exercise capacity.

The use of maximal exercise testing was introduced clinically in the mid-1980s and numerous published reports in the subsequent two decades generally supported the initial favorable impression of its utility in predicting operative morbidity and mortality after major lung resection (Table 19-2). Although specific guidelines have not yet been determined, most authors agree that the finding of a Vo₂max of less than 10 mL/kg/min puts a patient in an extremely high risk category for major lung resection, whereas a Vo₂max of more than 15 mL/kg/min is generally considered to be indicative of a patient with a standard risk for complications. The zone between the two values is indeterminate in terms of risk prediction. Some studies, including those reported by Bechard and Wetstein (1987) and Bolliger (1995a, 1995b), as well as those by Smith (1984) and Wang (2000) and their associates, that analyzed the potential utility of maximal exercise testing have demonstrated an important difference in the incidences of postoperative cardiopulmonary complications and mortality comparing patients with a low Vo₂max (<15 mL/kg/min) and those with a higher Vo₂max (<15 ml/kg/min). In contrast, others, such as Boysen (1990), Colman (1982), and Wang (1999b) and their co-workers, have found no predictive value for exercise capacity in assessing the risk for complications in lung-resection patients. In a prospective study, Brutsche and colleagues (2000) identified Vo₂max as an independent predictor of postoperative complications after major lung resection. More recently, predicted postoperative Vo₂max and Vo₂max expressed as a percentage of predicted have been suggested as effective parameters for risk stratification for major lung resection. Larsen and associates (1997) have noted that estimation of postoperative exercise capacity can be performed accurately using pulmonary perfusion scintigraphy. A Vo₂max of less than 50% of predicted is associated with an increased risk for complications and mortality, as reported by Bolliger (1995a) and Richter Larsen (1997) and their colleagues, and Bolliger and co-workers (1995b) suggested that operative mortality was excessive for a predicted postoperative Vo₂max of less than 10 mL/kg/min.

Less rigorous and less expensive techniques for assessing response to exercise as a means for estimating operative risk have been suggested. Mittman (1961) described an important but not statistically significant difference in mortality after cardiothoracic surgery associated with a decrease in arterial oxygen saturation measured by ear oximetry in response to exercise. A more recent study by Ninan and associates (1997) was performed on pneumonectomy patients

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and confirmed the predictive ability of this finding. However, a similar test carried out by Varela and colleagues (2001) demonstrated no utility of the development of desaturation in predicting postoperative complications. Holden (1992), Epstein (1995), and Brunelli (2002) and their co-workers observed that the mere ability to perform a certain amount of exercise, independent of monitoring of oxygen saturation, also is predictive of more favorable outcomes after major lung resection.

Table 19-2. Incidence of Postoperative Cardiopulmonary Complications Categorized According to Maximum Oxygen Consumption During Exercise (Vo₂max)^a

Author	Year	Patients (n)	Low Vo2max	High Vo2max	p Value
Smith et al.	1984	22	6/6	5/16	0.13
Bechard & Wetstein	1987	48	6/18	2/32	0.01
Epstein et al.	1993	42	8/14	10/28	0.19
Walsh et al.	1994	25	7/20	3/5	0.18
Bolliger et al.	1995a	80	8/17	8/63	0.002
Pate et al.	1996	9	2/4	0/3	0.25
Wang et al.	1999b	40	5/12	8/28	0.42
Wang et al.	2000	57	11/15	8/42	<0.001
aLow Vo2max, <15 mL/kg/min); high Vo2max, >15 mL/kg/min.

Blood Gases

Although many authors cite suggested values for pO₂ and pCO₂ that are intended to discriminate between normal and high-risk populations of patients for lung resection, the origin of these values is obscure. Early in the history of routine lung resection, some authors, including Curry and Ashburn (1950), Birath and Crafoord (1951), and Woodruff (1953) and Gaensler (1955) and their co-workers, as well as Mittman (1961), van Nostrand (1968), Lockwood (1973), Miller (1981), and Boysen (1981), either made no mention of blood gas measurements or stated that they were of little value in assessing operative risk. One exception was the report of Milledge and Nunn (1975) that described an increased need for postoperative ventilatory assistance in patients with hypoxemia and hypercapnia.

Hypercapnia, defined as a Pco₂ of more than 45 mm Hg, is normally a result of alveolar hypoventilation. Most patients with hypercapnia have a severely reduced FEV₁ and are at increased risk for complications after major lung resection. As a result, the identification of hypercapnia in such individuals is confirmatory and does not add additional information regarding operative risk. Many authors, such as Boushy (1970), Olsen (1975), Kohman (1986), the author (1988), Kearney (1994), and Harpole (1996) and coinvestigators, have been unable to demonstrate a significant relationship between elevated Pco₂ and the risk for respiratory complications or mortality after major lung resection. This finding must be tempered by the fact that, in most of these studies, patients were initially selected as candidates for operation based on preoperative blood gas analyses. Hypercapnia to levels of 45 to 55 mm Hg were not demonstrated by Glaspole and coauthors (2000) to affect outcomes after lung volume reduction surgery, whereas Szekely and colleagues (1997) suggested that an increased Pco₂ was associated with unacceptable outcomes after lung volume reduction surgery.

The situation regarding arterial oxygen levels is equally confusing. Olsen and coauthors (1975) stated that the combination of pulmonary hypertension and arterial hypoxemia (Po₂ <45 mm Hg) defined patients as being inoperable. Kohman and colleagues (1986) were unable to demonstrate a relationship between relative hypoxemia (Po₂ <65 mm Hg) and operative mortality after thoracotomy for lung cancer. Similarly, Harpole and associates (1996) were unable to demonstrate a relationship between Po₂ of less than 75 mm Hg and major morbidity after pneumonectomy. Markos and coauthors (1989) proposed that arterial hypoxemia (Po₂ <50 to 60 mm Hg) was a contraindication to lung resection. Hypoxia to levels of 45 to 55 mm Hg did not have a significant effect on complications after lung volume reduction surgery according to Glaspole and coauthors (2000), whereas Szekely and colleagues (1997) suggested that a decreased Po₂ was related to unacceptable outcomes after lung volume reduction surgery. Wang and associates (1999b) identified a modest difference in Po₂ values comparing patients with and without pulmonary complications after major pulmonary surgery.

Substantially increased Pco₂ or reduced Po₂ is likely to contribute to increased morbidity and mortality after major lung resection. The exact parameters permitting safe surgery may never be established.

Pulmonary Hemodynamics

An increase in pulmonary artery pressure and pulmonary vascular resistance was recognized early in the history of major lung resection as a normal response to surgery, as indicated in the reports of Cournand and Berry (1950), and Adams (1957), Burrows (1960), DeGraff (1965), and Harrison (1958) and their co-workers. Subsequent work by van Mieghem and Demedts (1989) quantified the changes, demonstrating an increase in pulmonary artery pressure of nearly 10% and an increase in pulmonary vascular resistance of almost 35% during exercise after major lung resection, changes that were associated with decreased exercise capacity but were clinically well tolerated. However, the magnitude of these alterations exposes patients with preexisting severe underlying lung disease to the risk for serious adverse consequences of major lung resection. The attendant long-term disability and high rate of mortality associated with such changes prompted the development of preoperative assessment of pulmonary vascular status before lung resection. For decades, pulmonary vascular compliance was assessed before pneumonectomy by measuring pulmonary artery pressure at rest and during exercise with unilateral pulmonary artery occlusion using a balloon as originally described by Carlens in 1951. Intraoperative assessment of pulmonary artery pressure during unilateral pulmonary artery occlusion was also used routinely by many surgeons, as illustrated by the reports of Pecora and Brook (1962) and van Nostrand and associates (1968), before proceeding with pneumonectomy. More recently, assessment of pulmonary vascular compliance has been accomplished using a balloon floatation catheter.

Abnormally elevated pulmonary vascular resistance or pulmonary artery pressure at rest, during exercise, or with unilateral pulmonary artery occlusion has been associated with a high rate of operative mortality after major lung resection, according to the studies of Pecora and Brook (1962), Uggla (1956), and Fee (1978) and van Nostrand (1968)

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and their colleagues. Abnormalities, such as dilated pulmonary arteries, suggesting the presence of pulmonary hypertension are often evident on preoperative CT of the lung-resection candidate. The use of invasive evaluations of pulmonary hemodynamics has been almost entirely supplanted by assessment of diffusing capacity and Vo₂max. In fact, Ribas and co-workers (1998) have noted that assessment of more global parameters, such as diffusing capacity, may be superior to measurement of pulmonary hemodynamics in predicting complications after major lung resection. Abnormal pulmonary hemodynamics in patients undergoing major lung resection are usually a result of severe underlying lung disease rather than abnormalities of the pulmonary artery or its main branches. As a result, most patients with underlying lung disease severe enough to compromise pulmonary hemodynamics exhibit substantial abnormalities of spirometry, diffusing capacity, and Vo₂max. In the few patients in whom a primary cause of abnormal pulmonary hemodynamics is thought to exist, echocardiogram or right heart catheterization is indicated. The presence of substantial pulmonary hypertension is a strong contraindication to major lung resection.

Age and Performance Status

Advanced age has always been considered a risk factor for lung resection. Prospective studies by Kohman (1986), Dales (1993), and Harpole (1999) and their associates have clearly identified a relationship between advancing age and an increased risk for operative mortality. Ginsberg and coauthors (1983) demonstrated that mortality rates more than doubled for each decade of age increase above the age of 60 years. Yusen and Trulock (1996), as well as Glaspole and co-workers (2000), have also documented that advanced age is a risk factor for mortality in patients undergoing lung volume reduction surgery. The author and co-workers (1995) have noted that advanced age has been shown to be an independent predictor of morbidity and mortality after major lung resection, with a twofold increase in the risk for complications for each decade increase in age.

A patient's performance status is always assessed informally during the preoperative period, but formal quantitation of performance status using a system such as that of the Eastern Cooperative Oncology Group (ECOG) is rarely performed by surgeons. Most surgeons intuitively identify patients with a performance status of 2 (less than 50% of waking time out of bed, but unable to perform self-care) to 4 (bedridden) as poor candidates for major lung resection. Formal classification of performance status permits assessment of the relationship between performance status and postoperative complications. Performance status has been shown by the author and Durkin (2003) to be an independent predictor of operative mortality after major lung resection. Each 1-point worsening in performance status increases the risk for postoperative mortality by a factor of 1.7.

RISK ASSESSMENT ALGORITHMS

The overall risk for morbidity after pulmonary resection is relatively high. A large number of predictive risk factors for major lung resection have been identified. These factors have stimulated research into risk assessment algorithms that would permit the preoperative calculation of the risk for complications in individual patients. Identification of such risks would help stratify patients into risk levels as an aid in appropriate selection of patients for lung resection. Patients determined to be at increased risk may benefit from preoperative cardiopulmonary rehabilitation, possibly reducing the incidence of complications. Identification of increased risk may permit use of increased resources for postoperative care. Risk stratification also makes possible comparison of outcomes among surgeons and among institutions for quality assurance purposes.

Systems that have been developed for general surgical conditions and procedures, such as POSSUM and APACHE II, have been applied to the evaluation of patients undergoing major lung resection by Brunelli and co-workers (1998, 1999) and Giangiuliani and associates (1990), respectively. These are cumbersome to use owing to the large number of variables that must be assessed in order to calculate a risk score. In addition, the predictive ability of these systems in lung-resection patients is only moderate. More specific systems have been developed for lung-resection patients, including the Cardiopulmonary Risk Index (CPRI) by Epstein and colleagues (1993), the Postoperative Predicted Product (PPP) by Pierce and co-workers (1994), the Predictive Respiratory Quotient (PRQ) by Melendez and Barrera (1998), and the EV D system by the author and Durkin (2003).

As an example, the EV D system is based on preoperative age, FEV₁, and diffusing capacity that the author and Durkin (2003) proposed. In this system, points are assigned for decade increments in age over 50 years, and for 10-percentage point decreases in FEV₁ and D_lco below 90% of predicted; the maximum number of points in any category is 4. The points are totaled to achieve an overall score from 0 to 12. The score is then assigned to a risk category (score 0 to 4 is minimal risk, 5 to 7 is low risk, 8 to 10 is moderate risk, and 11 to 12 is high risk). The relative risk for complications and mortality increases according to the calculated risk category for most types of complications except infectious complications (Fig. 19-8).

Unfortunately, no system has proved optimal for risk stratification for individual patients despite their relative ease of use. The overall accuracy of these systems in predicting complications is 70% to 80%. No single score value can serve as a threshold for differentiating among patients who are at normal risk and those at increased risk. The systems do, however, provide the ability to quantify a surgeon's general impression

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of a patient's overall status, which may enhance the surgeon's ability to select patients for surgery and to discuss with patients their relative risk.

Fig. 19-8. Incidence of complications after major lung resection according to risk and complication categories for the EV D system (based on preoperative spirometry, diffusing capacity, and age). (See text for details.) Data from Ferguson and Durkin (2003).

PREOPERATIVE EVALUATION FOR LUNG RESECTION

The outcomes outlined in the foregoing for the preoperative evaluation of the lung-resection candidate suggest a variety of limits precluding an acceptable operative result. Many of the parameters derive from studies performed in the 1950s through the 1980s. Since that time, there have been numerous improvements in the anesthetic management of pulmonary resection patients, making the intraoperative period much safer. The postoperative care of these patients has been altered in several ways. Postoperative pain management is routinely accomplished with continuous epidural infusion, subpleural infusion of local anesthetic, or patient-controlled intravenous analgesia, making what was once a very painful experience a procedure that is now well tolerated. The use of intensive pulmonary toilet exercises and early ambulation helps limit the incidence of pulmonary complications. Newer techniques for sealing air leaks and for chest tube management permit earlier discharge of patients, limiting their exposure to nosocomial infections and other complications.

In addition to these important changes, the introduction of lung transplantation and the growing practice of lung volume reduction surgery for severe emphysema have provided unparalleled clinical experience with the perioperative management of patients who have end-stage lung disease. For example, the criteria for entry into the study of the National Emphysema Treatment Trial (NETT) Research Group (2001) included a preoperative FEV₁ of less than 45%, a Pco₂ of less than 60 mm Hg, and a Po₂ of more than 45 mm HG, extending the traditional limits of resection. The study did outline a high-risk group for which surgery was deemed inadvisable: patients with an FEV₁ of less than 20% and either a D_LCO of less than 20% or homogenous distribution of their emphysema. This experience has confirmed the ability to anesthetize safely, operate on, and recover patients with extremely limited lung function and performance status.

In some instances, major lung resection may actually improve postoperative lung function, making lung cancer surgery safe in highly selected patients with severe emphysema. The patient selection criteria as outlined for the NETT Research Group are used (see Chapter 85), and patients are chosen for lobectomy who have their cancers in the target areas for lung resection that are most severely affected by emphysema, or undergo lung volume reduction surgery at the same time as lobectomy. In such carefully selected cases, the operative mortality is low, and most patients exhibit an increase in FEV₁, as observed by DeMeester (1998), Korst (1998), McKenna (1996), and Ojo (1997) and their associates. These findings suggest that accurate estimation of postoperative lung function may be particularly difficult in marginally operable patients with severe emphysema and that previously published limits for safe lung resection may be too conservative. Further studies are needed to permit identification of new limits for safe surgery in the lung-resection candidate.

In addition to operative survival, maintaining adequate long-term quality of life should be an objective in identifying candidates for major lung resection. It is to be expected that quality of life is considerably worse during the recovery phase after major lung resection than it would be long-term postoperatively. However, as recorded by Handy and colleagues (2002), a reduced quality of life is experienced by many patients more than 6 months after their lung operations. According to Cykert and associates (2000), conditions that patients find particularly worrisome for the long-term include ventilator dependence, dyspnea accompanying even mild exertion, dependence on supplemental oxygen, and inability to perform activities of daily living. Adverse changes in quality of life are a result of reduced exercise capacity, altered body image, and chronic pain. Interestingly, there is no apparent correlation between FEV₁ and postoperative quality of life, but a strong association exists between a low preoperative D_LCO and a poor long-term postoperative quality of life.

A suggested algorithm for assessing patients for lung surgery begins with a standard evaluation that includes a carefully performed history and physical examination, spirometry, and measurement of diffusing capacity (Fig. 19-9). Predicted postoperative FEV₁ and D_LCO expressed as a percentage of normal are calculated using the number of functioning lung segments as the denominator and the number of lung segments remaining after resection as the numerator of a fraction that is multiplied by the preoperative measured value to achieve a postoperative predicted value.

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For patients with a postoperative predicted FEV₁ of less than 40% or a postoperative predicted D_LCO of less than 40%, quantitative pulmonary perfusion scan is performed to assess regional lung function. This is particularly useful in patients with central lesions. The postoperative predicted values for FEV₁ and D_LCO are recalculated based on the results of the scintigram. If these values remain suboptimal, blood gases are obtained, and an exercise test to assess Vo₂max is performed. Criteria strongly suggesting inoperability include: Po₂ of less than 45 mmHg, Pco₂ of more than 60 mm Hg, predicted postoperative D_LCO of less than 20%, predicted postoperative FEV₁ of less than 20%, or a Vo₂max of less than 10 mL/kg/min.

Fig. 19-9. Suggested algorithm for evaluating patients for their suitability for major lung resection. ppoFEV1%, Predicted postoperative FEV₁ expressed as a percentage of normal; ppoD^lco%, predicted postoperative diffusing capacity expressed as a percentage of normal; pO₂: pO₂ in mm Hg; pCO₂: pCO₂ in mm Hg Vo₂max: oxygen consumption during maximum exercise in mL/kg/min).

ASSESSMENT OF RISK FOR OTHER PROCEDURES

The alterations in diaphragmatic function and resultant short-term perturbations in pulmonary function that occur after major thoracic or upper abdominal surgery are summarized earlier in this chapter. Despite the extensive number of data that have been generated regarding this topic, risk factors for thoracic surgical procedures other than standard lung resections have not been well defined. Similarly, risk factors for abdominal surgical procedures remain unidentified. In prospective studies by Fisher (2002), Lawrence (1989), and McAlister (2003) and their associates, neither hypercarbia nor reduced spirometry values were predictive of an increased risk for pulmonary complications. With two exceptions, the appropriate preoperative physiologic evaluation for the general thoracic surgical patient has not been determined. Those exceptions are the evaluation of the lung resection candidate as outlined earlier in this chapter and possibly candidates for esophagectomy.

The physiologic evaluation of candidates for esophagectomy has been explored in some detail. The impetus to evaluate esophagectomy patients lies in the high rate of postoperative pulmonary complications that are associated with this operation. Based on retrospective studies, the physiologic predictors of an increased risk for pulmonary complications after esophagectomy are advanced age and reduced FEV_1. In a study by the author and Durkin (2003), patients with pulmonary complications had an FEV₁ of 88% compared with a value of 99% in patients without pulmonary complications. Another study conducted by Avendano and colleagues (2002) identified the finding of an FEV₁ of less than 65% as a significant independent risk factor for postoperative pulmonary complications. Nagamatsu and co-workers (2001) reported that there also was evidence that measurement of oxygen consumption during exercise may help predict complications, but this technique requires further scrutiny. At present, routine pulmonary function testing of esophagectomy patients is not warranted. However, such testing is recommended for patients with clinically evident impairment of pulmonary function to assist in the evaluation of pulmonary risk and to enable optimized preoperative and postoperative care for those patients determined to be at increased risk.

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