RATIONALE
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Provide a rational basis for discussing risks and outcomes with patients.
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Help with issues surrounding informed consent.
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Assist in patient selection for major surgery.
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Enable discussions among caregivers and with referring physicians about risks and expectations.
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Populate databases to enable development of risk models that will assist with all of the above.
DEFINITIONS
The preoperative evaluation of thoracic surgery patients includes a general assessment of the patient’s status, knowledge of the diagnosis or possible diagnoses for which surgery may be performed, and a set of focused tests that evaluate the patient’s physiologic ability to undergo the proposed operation. This chapter will not deal with diagnostic or staging studies that are aimed at determining the appropriateness of surgery for a specific condition or whether the operation is feasible from a technical aspect.
HISTORY
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The association between lung function and long-term survival was initially described in 1846 by Hutchinson.
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Gaensler first introduced the concept of timed expiratory function as a means for assessing pulmonary insufficiency and its relation to postoperative outcomes after lung surgery (1951).
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As lung resection for cancer became commonplace in the 1960s and 1970s, and additional measures of pulmonary reserve were introduced
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Maximum ventilatory volume in 1 min (MVV)
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Postoperative predicted FEV1
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FEV1 expressed as a percent of predicted for age, height, and gender.
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Lung spirometric function currently used to develop actuarial tables for life insurance purposes and for estimating survival after lung cancer resection.
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In the 1980s, gas exchange, oxygen consumption, and other forms of exercise testing were introduced as additional measures to assess risk after lung resection.
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Single-breath diffusing capacity for carbon monoxide (DLCO)
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Maximum oxygen consumption during exercise (VO2max)
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Stair climbing test and other measures of exercise capacity
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In the 1980s and 1990s, clinical databases were first used to identify individual risk factors for complications and mortality after major lung resection; databases for esophagectomy were slower to develop.
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In the 1990s and subsequently, risk models were first developed for prediction of outcomes after major lung resection; predictive models for esophagectomy outcomes were infrequent. No predictive models were developed for other major thoracic surgery.
AGE
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Historically, advanced age confers increased risk of mortality after major thoracic surgery.
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There is no specific age cutoff for prohibitive risk.
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Recent reports suggest that age is declining in importance as a risk factor for mortality, possibly because of improved patient selection and perioperative management.
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Advanced age continues to be associated with an increased risk of postoperative complications.
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A recent systematic review of pulmonary risk stratification in mainly noncardiothoracic surgery (but included major esophageal and aortic surgery) reported that advanced age conferred higher odds for postoperative pulmonary complications (age 60 to 69 years: odds ratio 2.09 [1.66-2.64]; age 70 to 79 years: odds ratio 3.04 [2.11 to 4.39]).
PERFORMANCE STATUS
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Performance status should be assessed in every patient considered for major thoracic surgery.
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It is a fundamental element in decision making about major thoracic surgery.
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Measures of performance status include the Eastern Cooperative Oncology Group (ECOG) performance status criteria ( Table 3-1 ) and Karnovsky performance status criteria ( Table 3-2 )
TABLE 3-1 ▪
EASTERN COOPERATIVE ONCOLOGY GROUP PERFORMANCE STATUS CRITERIA
Score
Description
0
Fully active, able to carry on all predisease performance without restriction
1
Restricted in physically strenuous activity but ambulatory and able to carry out work of a light or sedentary nature, e.g., light housework, office work
2
Ambulatory and capable of all self-care but unable to carry out any work activities. Ambulatory more than 50% of waking hours
3
Capable of only limited self-care; confined to bed or chair more than 50% of waking hours
4
Completely disabled. Cannot carry on any self-care. Totally confined to bed or chair
5
Dead
TABLE 3-2 ▪
KARNOVSKY PERFORMANCE STATUS CRITERIA
Score
Description
100
Normal: no complaints, no evidence of disease
90
Able to carry on normal activity; minor symptoms
80
Normal activity with effort; some symptoms
70
Cares for self; unable to carry on normal activities
60
Requires occasional assistance; cares for most needs
50
Requires considerable assistance and frequent care
40
Disabled: requires special care and assistance
30
Severely disabled: hospitalized but death not imminent
20
Very sick: active supportive care needed
10
Moribund: fatal processes are progressing rapidly
0
Dead
THORACIC SURGERY: PERIOPERATIVE PULMONARY PATHOPHYSIOLOGY
A number of physiologic aberrations occur perioperatively in the thoracic surgical patient (see later).
Note: In patients with pre-existing pulmonary conditions, these sequelae can compound the already abnormal lung mechanics and gas exchange evident in these patients.
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Diaphragm dysfunction:
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Impaired force production and endurance capacity due to :
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Direct injury to diaphragm or phrenic nerve
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Lengthening contraction-induced muscle injury
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Impaired force due to prolonged mechanical ventilation
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Altered chest wall/lung compliance with increased work of breathing
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Reduced shortening fraction of the diaphragm
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Reduced central drive (reflex; opioids)
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Contiguous inflammatory process
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Sepsis
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Metabolic derangements
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Diaphragm dysfunction can last several weeks
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Diaphragm dysfunction is similar with thoracotomy and with video-assisted thorascopic surgery (VATS), except that recovery time is shorter with VATS
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Abnormal lung function
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In early postoperative period, FEV1 and forced vital capacity (FVC) reduced about 35 to 50%. From those predicted values according to extent of resection.
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Slightly greater decrement in FVC with thoracotomy compared with VATS.
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By discharge, values approach 80% of predicted values according to extent of resection.
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Functional residual capacity (FRC) is reduced about 30% in the early postoperative period.
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It can take up to 3 to 4 months to approach postoperative predicted values.
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Gas exchange
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Microatelectasis contributes to hypoxemia (reduction in lung volumes; abnormal mucociliary clearance)
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Hypercapnia can occur due to central respiratory depression (opiate analgesia, residual effects of anesthetic agents), incomplete reversal of neuromuscular blockade, diaphragm dysfunction, splinting and abnormal rapid-shallow breathing pattern
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PULMONARY FUNCTION
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Definitions and determinants
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FVC (forced vital capacity): the amount of air that can be forcefully exhaled from total lung capacity to residual volume, in a single breath, is determined by several factors aside from height (positive correlation) and age (negative correlation).
Determinants are :
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Inspiratory muscle strength
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Elastic recoil forces of the lung
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Chest wall compliance
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Dynamic closure of airways (and thus the balance between lung recoil and airways resistance upstream of a flow limiting collapse point)
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Expiratory muscle strength
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Patient cooperation and ability
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FEV1 (forced expiratory volume in one second): the amount of air that can be forcefully exhaled in the first second of an FVC maneuver.
Determinants are:
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Factors determining flow, such as lung recoil and airways resistance upstream of a flow limiting collapse point
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Reduced in the presence of restriction of lung volume (in proportion to curtailment of FVC or increased in relation to FVC, in the presence of increased lung recoil)
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MVV (maximum ventilatory volume): the total volume of air that can be cycled during 1 min of maximum ventilation (extrapolated from a 12- or 15-second maneuver)
Determinants are:
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Elastic and flow resistive factors determining flow
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Respiratory muscle strength
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Respiratory system coordination
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Can be disproportionately reduced relative to the FEV1 (lower limit = FEV1 × 32.8) with neuromuscular weakness, upper airways obstruction, and poor effort
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DLCO: single breath diffusing capacity for carbon monoxide (also termed transfer factor)
Determinants are:
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Total surface area available for gas exchange
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Membrane thickness a minor factor
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Total capillary blood volume
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Hemoglobin concentration
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Maldistribution of gas
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Carboxyhemoglobin concentration
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VO2max: highest oxygen consumption achievable during maximal effort for an incremental exercise test and fails to increase further, i.e., plateaus. Usually we measure the maximum VO2, which is the highest VO2 achieved with a maximal effort (this may equal or be similar to VO2max, but not in all cases).
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Evaluation
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Essential before major lung resection
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Recommended for many patients undergoing esophagectomy
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Of little value in patients undergoing lesser operations unless respiratory status is tenuous
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Impaired pulmonary function is associated with
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Preoperative chemoradiotherapy
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Increased risk of pulmonary complications and mortality after major lung resection
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Increased risk of pulmonary complications after esophagectomy
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Assessment of pulmonary function prior to major lung resection
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Use of spirometric values in predicting risk of major lung resection
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Preoperative threshold values for increased risk:
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FEV1 less than 2 L or less than 60% predicted
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MVV <50% predicted
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Predicted postoperative (ppo) threshold values for increased risk
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ppoFEV1 less than 800 to 1000 mL
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ppoFEV1 less than 40%
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Estimates of ppo values calculated using percentage of functioning lung postoperatively based on :
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Percentage of functioning lung segments remaining after resection based on location of primary tumor
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Quantitative ventilation/perfusion scan
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Quantitative computed tomography (CT) densitometry
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Oxygen exchange/consumption in predicting risk of major lung resection
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Some assessment should be performed routinely, not just in patients with impaired spirometry
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Lowest cost technique is measurement of oxygen saturation during two-flight stair climb
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Maintenance of saturation in normal range indicates of low risk
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Desaturation or inability to complete stair climb indicates high risk
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Inability to complete stair climb test indicates of prohibitive risk
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A moderate-cost , high-accuracy technique is DLCO; DLCO predicts operative outcomes even in patients with normal spirometry ; high risk is associated with
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DLCO less than 60%
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ppoDLCO less than 40%
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Highest cost , high-accuracy assessment is measurement of VO2max :
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Normal risk VO2max: higher than 15 to 20 mL/kg/min (>60% to 70% predicted)
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High risk VO2max: 10 to 15 mL/kg/min (50% to 60% predicted)
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Prohibitive risk VO2max: less than 10 mL/kg.min [less than 40% to 50% predicted]
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An algorithm for assessing pulmonary status before major lung resection is shown in Figure 3-1
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