INTRODUCTION
Patients who develop pulmonary lesions requiring resection often have underlying parenchymal lung abnormalities. Pulmonary function tests may reveal clinically significant obstruction or gas diffusion abnormalities, which require careful consideration; a patient’s immediate operative risks and possible long-term disability related to loss of lung function must be weighed against the benefit of a potentially curative surgery for lung cancer. Numerous studies have examined methods of preoperative risk Zassessment for these patients, and although individual findings vary, a general consensus for risk stratification has begun to emerge, as recently outlined in an algorithm by the American College of Chest Physicians (ACCP) ( Fig. 31-1 ). In this chapter, we provide a background for understanding the current guidelines, discuss high-risk patient groups who do not meet usual criteria for surgery, and describe the application of these guidelines in practice.
LUNG CANCER RESECTION: STRATIFICATION OF RISK
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Who does not need further workup?
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There is general consensus that those with an FEV 1 of greater than 80% predicted have an average perioperative risk.
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If a patient has a preserved FEV 1 , but unexplained dyspnea or diffuse parenchymal disease on chest computed tomography (CT) scan, ACCP 2007 guidelines recommend measuring carbon dioxide diffusing capacity (DLCO).
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Patients with a DLCO of less than 80% predicted may have increased pulmonary complications ( Table 31-1 ); those with less than 60% predicted may have increased mortality.
TABLE 31-1 ▪
PERIOPERATIVE COMPLICATIONS *
Need for prolonged (more than 48 h) mechanical ventilation or reintubation
Myocardial infarction
Cardiac arrhythmias requiring treatment
Pneumonia
Atelectasis—on radiologic studies or lobar requiring bronchoscopy
Pulmonary embolism
Acute CO 2 retention
Death
* Complications included in most studies examining predictive value of pulmonary function tests and cardiopulmonary exercise tests in estimating perioperative risks for lung cancer resection surgery.
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Patients with an FEV 1 greater than 80% predicted and DLCO greater than 80% predicted do not have increased risk for lobectomy or pneumonectomy, and do not require further preoperative testing .
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Next step in evaluation: split-function determinations
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Patients with FEV 1 or DLCO less than 80% predicted require further evaluation
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The ACCP 2007 algorithm and other sources suggest split-function evaluation for determination of predicted postoperative (ppo) FEV 1 and DLCO values as next step (see Figs. 31-1 and 31-2 ).
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Split-function evaluation can be done by using CT scan data or by a nucleotide lung perfusion scan (see Fig. 31-2 ).
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Nucleotide lung perfusion scan is best for patients with marginal lung function and/or for patients requiring pneumonectomy.
Figure 31-2
Calculation of predicted postoperative pulmonary functions. Formula used is determined by degree of impairment and degree of resection required (see text).
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Risk stratification based on ppo lung functions
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For ppoFEV 1 less than 40% predicted, the perioperative mortality rate is approximately 50%.
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ppoDLCO of less than 40% predicted is also associated with high mortality and morbidity.
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When the product of the ppoDLCO and ppoFEV 1 is less than 1650, this number predicts increased surgical mortality.
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ppoDLCO as % predicted closely correlated with operative mortality: odds of death increased 3.5-fold for every 20-point decrease in ppoDLCO%.
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DLCO can be decreased by induction (preoperative) chemotherapy, and this decrease in DLCO is an additional risk factor for postoperative complications ; therefore, repeating pulmonary function tests after induction treatment should be considered.
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In some studies, even patients with ppoDLCO or ppoFEV 1 of less than 40% can have uncomplicated postoperative courses, but mortality risk is higher and physician discretion is important in these patients.
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Next step in evaluation: cardiopulmonary exercise testing (CPET):
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CPET is recommended for further evaluation of patients with ppoFEV 1 or ppoDLCO of less than 40%.
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Determination of VO 2 max via CPET can be the next step instead of a split-function test in some algorithms.
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Incremental exercise testing—Most widely used and studied type of exercise test for assessing preoperative risk in high-risk patients.
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Patient exercises on a cycle ergometer or treadmill, with continuous (ramp) or incremental increase each minute in work rate; continuous exhaled O 2 and CO 2 measurements, electrocardiogram (ECG) and O 2 saturation, and intermittent blood pressure readings are measured.
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Work rate increments targeted based on patient’s predicted VO 2 max to reach maximal exercise within 6 to 12 minutes.
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Risks of complications during exercise testing are low, with overall rate of death of 2 to 5 per 100,000 clinical exercise tests; risks are related to underlying comorbid conditions.
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Absolute contraindications are few and include syncope, unstable angina, uncontrolled systemic hypertension, and the presence of serious dysrhythmias on resting ECG.
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In patients with multiple or no medical conditions, the many variables measured allow detailed analysis and determination of etiology of impaired exercise tolerance or unexplained dyspnea
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For patients with lung cancer, the most frequently used parameter for preoperative assessment and risk stratification is VO 2 max.
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VO 2 = cardiac output × oxygen extraction.
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Maximal VO 2 can be reduced for many reasons ( Fig. 31-3 ).
Figure 31-3
Peak VO 2 (maximum delivery to and extraction of oxygen from tissues) can be limited by multiple factors:
A, Normal: VO 2 max is limited by reaching maximum cardiac output via maximum heart rate (stroke volume reaches plateau earlier)
B, Maximum heart rate reached at lower level of exercise (and O 2 extraction from tissues):
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Heart disease: maximum cardiac output impaired, usually due to impaired stroke volume (reach maximum heart rate early).
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Deconditioning: decreased stroke volume and extraction of oxygen from tissues leads to maximum heart rate and fatigue early.
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C, Limited by factors other than heart rate (with increased heart rate as compensatory mechanism):
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Respiratory disease: oxygenation impaired, arterial oxygen decreased and limits oxygen delivery, causing lactic acidosis and fatigue, exercise terminated.
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Pulmonary vascular disease: oxygenation and stroke volume impaired, both limiting oxygen delivery, causing lactic acidosis and fatigue, exercise terminated.
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Anemia: impaired oxygen content/delivery to tissues, causing lactic acidosis and fatigue, exercise terminated.
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Peripheral vascular disease: impaired delivery of blood/oxygen to tissues, causing lactic acidosis and fatigue, exercise terminated.
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Mitochondrial disease: oxygen extraction impaired, causing lactic acidosis and fatigue, exercise terminated.
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D, Limited by factors not related to oxygen delivery:
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Respiratory disease: ventilation impaired, CO 2 rise causes dyspnea and exercise terminated.
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Anxiety, poor motivation.
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E, Elite endurance athlete: Stroke volume and oxygen extraction supraphysiologic, with resultant VO 2 much higher at maximum heart rate.
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This multifactorial variable is most often the best predictor of perioperative risk (see below).
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Risk assessment based on CPET
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Patients with a preoperative VO 2 max of greater than 15 to 20 mL/kg/min, or greater than 75% predicted have acceptably low perioperative mortality rates.
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Patients with a VO 2 max between 10 and 15 mL/kg/min are at an increased risk for perioperative complications (see Fig. 31-1 )
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Percent predicted VO 2 max may be a better discriminator than absolute VO 2 max, and patients with a VO 2 max of less than 60% predicted are at increased risk for perioperative complications.
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A low anaerobic threshold (<11 mL/min/kg), especially in conjunction with cardiac ischemia, is associated with a high mortality rate.
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Patients with a ppoVO 2 max of less than 10 mL/kg/min have a very high perioperative mortality rate and are generally considered to be inoperable.
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Even patients who are deemed inoperable by the above-mentioned criteria can successfully undergo surgery, and median survival for these patients is twice as long as for patients who do not undergo surgery (30 vs 15 months).
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Presurgical exercise training can increase VO 2 max by 2 or more mL/kg/min in borderline patients within 4 to 6 weeks.
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Fixed challenge exercise testing: assessment of ability to perform a fixed amount of work; that is, climbing stairs or walking a fixed distance :
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Stair climbing:
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Classic test for estimating perioperative risk—usually involves physician accompanying patient to climb stairs in a hospital or office building at patient’s own pace with monitoring pre-exercise vital signs, continuous pulse, and O 2 saturation during climb, and postexercise vital signs; some studies include calculation of VO 2 max by estimation of work done (step height × steps/min × wt in kg × conversion factor).
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Inability to climb 12 meters, or 75 steps, predicts a high rate of complications (>50%).
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Ability to climb three flights, or 90 steps, predicts a lower rate of perioperative complications (6–20%).
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6-minute walk test:
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Patient is instructed to walk at a brisk pace in a hallway for 6 minutes and is allowed to rest as needed during the interval; total distance walked is recorded.
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Data are limited in this test in preoperative assessment of lung cancer patients.
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One study demonstrated that a 6-minute walk distance of greater than 1000 feet predicted successful surgical outcome.
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