For example, the risk of pulmonary complications is predicted by spirometry in patients undergoing esophagectomy, and operative mortality after esophagectomy may similarly be related to preoperative pulmonary disease.
Risk Factors Specic risk factors for major thoracic surgery related to pulmonary function include chronic pulmonary disease emphysema, chronic bronchitis, asthma and any condition that limits lung volume, including a large pleural effusion, a large diaphragmatic hernia, and prior major lung resection.
Interstitial lung disease that interferes with gas exchange may be associated with hypoxia. Induction chemotherapy and radiotherapy result in measurable decrements in lung function.
Similarly, distant prior radiotherapy to the lung or mediastinum can cause considerable impairment of pulmonary function as well as decreasing chest wall mobility and limiting mediastinal motion. In addition to these conditions, many of which cause chronic changes in lung function, performance of a thoracotomy has acute detrimental effects on spirometry that persist for up to 8 to 12 weeks postoperatively. Sixty percent decreases in forced vital capacity FVC and forced expiratory volume in 1 second FEV1 also occur during this period.
Furthermore, these reductions persist because of permanent loss of lung volume and are sometimes associated with impaired exercise capacity, particularly in patients who have undergone pneumonectomy.
In order to properly select patients who can be shepherded through the acute recovery period after major lung resection and some other types of thoracic surgery, a careful preoperative assessment of lung function and estimation of expected postoperative function is essential in the evaluation of the lung resection candidate.
Spirometry Spirometry has been used to assess operative risk in lung resection candidates for more than 5 decades. FVC was. Calculation of a predicted postoperative value for FEV1 ppoFEV1 has proved to be very useful in estimating a patients postoperative risk. However, this parameter is strongly dependent on patient effort and therefore is subject to tremendous variability. Traditional cutoff values for FVC and FEV1 that are used to differentiate between low and high risk for major pulmonary resection are relatively inaccurate at the extremes of the body mass spectrum.
In consideration of this fact, spirometric values expressed as a percentage of the predicted value based on age, gender, and height have more commonly been used to assess operative risk. The calculation of predicted postoperative values is sometimes challenging.
In patients with normal lung function who do not often need major lung resection , the simplest method is to multiply the preoperative spirometric value by the fraction of functional lung segments expected to remain postoperatively. The calculation becomes more important in patients with marginal lung function, especially those who have areas of functional heterogeneity, and in patients who have undergone prior lung resection.
Lung segments that are obstructed are eliminated from calculations in order to more accurately. DLco, diffusing capacity of the lung for carbon monoxide; FEV1, forced expiratory volume in 1 second; ppo, predicted postoperative. Lobes that are affected by emphysema to a greater extent than the remaining lung are not considered fully functional for purposes of calculating estimated postoperative function.
Several techniques are available that enable renement of the calculation of estimated postoperative function. Quantitative pulmonary scintigraphy, using the perfusion phase of the examination as the best estimate of regional function, effectively estimates regional lung function assessed per quadrant or per lung.
A newer method, quantitative computed tomography CT , provides similar or greater accuracy through measurement of relative lung density as an estimate of pulmonary vasculature Bolliger et al, In addition to the utility of spirometry in estimating postoperative risk after major lung resection, it is also effective in predicting the risk of pulmonary complications after esophagectomy.
Rather, spirometry may be appropriate to perform in patients who have clinical evidence of underlying lung dysfunction as a means to estimate the risk of postoperative pulmonary complications.
If that risk is high, interventions such as preoperative cardiopulmonary rehabilitation may be appropriate, and a more accurate informed discussion can take place with the patient. Diffusing Capacity Until the late s, the only reliable method of assessing lung function as a means for predicting complications in patients undergoing thoracic surgery was spirometry. The measured and postoperative estimated values failed to predict most pulmonary complications and postoperative mortality, particularly in patients undergoing major lung resection.
Subsequent studies identied diffusing capacity as an independent and important predictor of incremental risk of postoperative pulmonary morbidity and overall mortality after major lung resection. In the absence of severe pulmonary dysfunction, DLCO assessment in patients undergoing lesser lung operations is of questionable value; DLCO measurement in patients with severely compromised lung function may assist the physician in having an informed discussion with the patient about potential risks and outcomes.
In addition to its utility in assessing risk related to major lung resection and LVRS, the DLCO predicts the incremental risk of pulmonary complications in patients undergoing esophagectomy. Therefore, routine measurement of DLCO is not generally indicated in this patient population.
Exercise Capacity and Oxygen Consumption Another method of assessing operative risk for major lung resection is measurement of exercise capacity. This is accomplished with simple techniques such as the 6-minute walk distance, stair climbing ability, and assessment of arterial oxygen saturation PaO2 during walking on at ground or during stair climbing.
However, incremental risk is difcult to establish using these semiquantitative methods. It is often appropriate to further evaluate patients who are deemed to be at substantially increased risk for complications after major lung.
This technique is expensive and labor intensive, and its accuracy depends to some extent on the patients willingness to exercise to capacity and on the ability of the physician who is supervising the test to determine when the point of maximum exercise has been achieved. With these caveats in mind, the objective data that result from this test provide estimates of risk that are similar or greater in accuracy to those provided by more standard measurements such as spirometry and DLCO.
Efforts have been made to correlate risk with. Lung Function and Long-Term Outcomes In addition to the immediate postoperative risk of morbidity and mortality after major thoracic surgery, long-term QOL and overall survival must be considered when making surgical recommendations to patients. The inuence of pulmonary function on long-term outcomes has been best dened for patients undergoing major lung resection and often reects processes that are characteristic of a general population.
It has been known for centuries that life expectancy in the general population is inversely related to FVC, and insurance companies have recently begun to use spirometry as part of their actuarial analyses in setting life insurance rates.
Similarly, long-term survival in patients with lung cancer is related to the severity of chronic obstructive pulmonary disease LopezEncuentra et al, Weight this factor against the relative risk of death from recurrent cancer based on the type of lung resection performed.
As part of the initial evaluation of such patients, a careful history and a thorough physical examination are vitally important in identifying problems that portend an increased risk of postoperative cardiovascular complications, including stroke, myocardial infarction, and arrhythmia. In general, the risk of cardiovascular complications is much higher in patients undergoing major thoracic surgery than in those undergoing less stressful types of general surgical procedures.
Coronary Artery Disease Risk factors for postoperative coronary artery complications include ischemic heart disease, congestive heart failure, dia-. FIGURE An algorithm for assessing risk of mortality and postoperative complications based on pulmonary function in patients who are candidates for major lung resection. Box Factors Associated With Increased Risk of Cardiovascular Complications After Major Thoracic Surgery Major Unstable coronary syndromes Recent myocardial infarction with ongoing ischemic risk Unstable or severe angina Decompensated congestive heart failure Signicant arrhythmia Severe valvular disease Pulmonary hypertension Intermediate Mild angina pectoris Prior myocardial infarction by history or pathologic Q waves Compensated or prior congestive heart failure Diabetes mellitus Advanced age Low functional capacity e.
Chest SS, Patients who have unstable angina or recent myocardial infarction must undergo a thorough evaluation, and any elective surgery is postponed until such conditions are stabilized. An algorithm for managing patients with one or more risk factors is outlined in Figure Specic testing is performed when the clinical situation indicates that changes in management would occur if the test returned positive, suggesting that the algorithm is cost-effective.
Further testing is not performed if the results would not inuence a patients overall management strategy. The likelihood of perioperative complications in patients with these risk factors may be reduced through revasculariza-. Stenting requires administration of antiplatelet agents, including aspirin and clopidogrel, for a period of at least 4 to 12 weeks after stent placement and aspirin indenitely afterward. Performance of major surgery before the end of the 4- to week period leads to unacceptable risks of bleeding if antithrombotic agents are not discontinued or to myocardial infarction in those patients in whom antithrombotic agents are stopped preoperatively.
Some newer drug-eluting stents require intensive antithrombotic therapy for even longer periods before the risk of stent thrombosis is sufciently small to permit discontinuation of these medications preoperatively.
Both aspirin and clopidogrel must be discontinued for 5 to 7 days before major surgical intervention to reduce the risk of surgical bleeding. CABG before thoracic surgical intervention is appropriate in patients in whom important coronary artery disease is not amenable to percutaneous revascularization techniques. There is no specied interval that must be observed between successful coronary artery surgery and subsequent major thoracic surgery.
The surgeons clinical judgment about the patients condition and ability to withstand further major surgery is the best means for determining suitable timing. It remains to be seen whether the routine use of minimally invasive approaches to off-pump coronary artery bypass surgery can meaningfully decrease the necessary time interval between operations.
Of note, there is rarely an imperative to perform a major thoracic procedure under the same anesthesia used for CABG.
Extensive operations for lung resection are usually performed less thoroughly through a median sternotomy than they are through a transthoracic approach, which may potentially compromise the therapeutic efcacy of interventions for oncologic problems.
In addition, manipulations of tumor tissue before or during periods when patients are on cardiopulmonary bypass theoretically increase the risk of bloodborne distant metastatic disease.
Finally, the use of anticoagulation, which is frequently necessary for performing coronary artery bypass, increases the risk of bleeding from the thoracic surgical sites, and these sites may not be easy to identify or control if such bleeding occurs.
Additional medical management suitable for most patients with at least one risk factor includes administration of blockers in the perioperative period. The medication is begun 2 to 7 days preoperatively and is continued for at least 1 week postoperatively.
The dose is titrated to reduce resting heart rate to about 60 beats per minute. Risk Factors for Postoperative Arrhythmias Cardiac arrhythmias, particularly supraventricular arrhythmias, occur commonly after major thoracic surgery. Risk factors Ischemic heart disease Congestive heart failure Diabetes mellitus Renal insufficiency Poor performance status.
FIGURE An algorithm for evaluating and minimizing the risk of cardiovascular complications in patients undergoing thoracic surgical procedures. CABG, coronary artery bypass grafting. In efforts to prevent such complications, which develop most frequently after pneumonectomy and esophagectomy, prophylactic regimens are sometimes recommended for patients at increased risk.
Elevated risk is associated with advanced age, greater extent of lung resection, mediastinal surgery thymus, mediastinal tumor, esophagectomy , and possibly a low DLCO Vaporciyan et al, Systemic Anticoagulation in the Perioperative Period Conditions requiring preoperative anticoagulation are not uncommon among thoracic surgical patients.
Anticoagulation is necessitated most commonly by acute conditions, including venous thrombosis and pulmonary embolism, and by chronic conditions such as recurrent venous thrombosis, a mechanical heart valve, or atrial brillation.
In the setting of chronic conditions such as prior venous thrombosis, atrial brillation, or distant prior pulmonary embolism, anticoagulation is. In contrast, patients with mechanical articial valves or more acute thrombotic problems require anticoagulation until the day of the operation.
This is most easily achieved by using either IV heparin in an inpatient setting or enoxaparin injections until 8 to 12 hours before the planned incision time.
Anticoagulation therapy is resumed as soon as the risk of bleeding is substantially reduced, typically not until the day after surgery. In any case, assessment of the increased risks associated with diabetes enables the surgeon to have an informed discussion. Impaired renal function poses important challenges during the preoperative evaluation of thoracic surgical patients. Use of contrast material as part of staging studies is often contraindicated, reducing the accuracy of such studies and adding potential uncertainty to the outcome of any operation.
Perioperative management in such patients requires a careful review of medications to be used, with appropriate dose reduction or altered dose scheduling based on the degree of functional renal impairment. For patients who are undergoing hemodialysis, arrangements must be made for this to be performed on the day before surgery, so that dialysis on the day of surgery is avoided, reducing the risk of bleeding associated with heparin needed for hemodialysis.
Patients who are receiving peritoneal dialysis and who require a laparotomy must be converted for the short term to hemodialysis, usually through a temporary venous catheter rather than a shunt or stula. The presence of renal failure is associated with poorer outcomes for most important general thoracic procedures, including major lung resection,63,64 and it is appropriate that this be discussed as part of the informed consent process.
Hepatic insufciency presents considerable challenges for performing thoracic surgery, including increased risks of bleeding from coagulopathy, hemorrhage from esophageal varices, hepatic encephalopathy, and uncontrollable ascites.
Patients with suspected cirrhosis are evaluated according to standard systems such as the Child classication, which requires assessment of serum bilirubin and albumin, prothrombin time, degree of encephalopathy, and amount of ascites. Carefully selected patients in Childs group A or possibly group B may be candidates for major lung resection or esophagectomy, with the anticipation that their risks of operative complications are considerably increased.
General physical limitations sometimes become important in the preoperative evaluation of the thoracic surgery patient. Patients with lower extremity amputations e. Patients who cannot ambulate independently using a limb prosthesis must be assessed with regard to their ability to ambulate as part of their recovery from surgery. This may not be an important issue if a muscle-sparing thoracotomy is performed because this procedure preserves shoulder girdle musculature and function and does not affect the use of walking aids.
However, it may be a complicating factor if a sternotomy or transverse sternothoracotomy is performed because ambulation using a walker or crutches places unusual stresses on the reapproximated sternum, possibly leading to dehiscence and infection or simple malunion. Airway issues affect any patient who requires lung isolation as part of a thoracic surgical procedure.
Lung and esophageal cancers share common risk factors with head and neck cancer, and it is not uncommon for a patient to require surgery for more than one of these conditions over time. Patients who. This must be considered before major thoracic surgery is recommended.
The collective effect of comorbidities has an important inuence on both short-term and long-term outcomes after thoracic surgery. Higher comorbidity scores are associated with an increased risk of postoperative complications after major lung resection. Risk assessment tools in thoracic surgery are in their infancy, compared with the robust tools available for risk assessment in adult cardiac surgery. The use of such algorithms is potentially important in informing individual patients about risk levels, in determining the potential utility of preoperative interventions for lowering risk, and in assessing the need for enhanced resources during the postoperative care of such patients.
Various scoring systems have been used to provide a reasonably accurate quantitative estimate of risk for patient populations undergoing major lung resection and other operations. They are currently most useful for estimating outcomes in populations undergoing major lung resection that are stratied according to standard risk proles.
In making such recommendations, the goals of the surgeon and of the patient must be explicitly expressed and assessed; they are not always similar, and in many cases they are quite disparate. Patients tend to follow their self-interest by seeking procedures and outcomes that minimize discomfort and optimize QOL; death as an outcome of surgery does not pose nearly as great a concern as does permanent postoperative disability Cykert et al, Most risk factors described in this chapter are well understood and are indelibly etched into the minds of surgeons who deal with these patients on a daily basis.
The scoring. Potential methods to do this include the use of articial intelligence software to train a neural network based on actual outcomes. However, at present, a trained neural network is site specic, making its use feasible only in high-volume centers in which infrastructure is available to manage the network.
No current scoring or articial learning systems can provide insight into long-term outcomes, including QOL and longterm survival. In fact, the necessary tools to measure QOL in the specic context of thoracic surgical procedures have not yet been devised or validated.
Until such measures are developed, surgeons and their patients will not have the ability to make truly informed decisions about the utility of surgery. Decision analysis models are being developed as methods to appropriately weigh risks and benets for patients undergoing thoracic surgery. Some issues that have been assessed include the utility of various treatments surgical and nonsurgical for achalasia, whether to perform routine mediastinoscopy for staging of surgical candidates for lung cancer resection, and the choice between sleeve lobectomy or pneumonectomy for centrally located lung cancers.
Such models, using data relevant to individual patients, may prove very useful in providing patientspecic risk estimates and guidelines for recommendations. Despite the promising work that is being done on risk analysis and decision-making algorithms, the evaluation of potential thoracic surgical patients currently remains an art that ultimately is dependent on the experience and judgment of the surgeon.
The assessments outlined in this chapter provide useful algorithms for consideration of risks and outcomes in patient populations and in individual patients.
Use of these algorithms must be tempered by the surgeons knowledge of an individual patients risks, needs, and desires. It is unlikely that this vital judgment function will ever be completely subsumed by technological advances. One must try to establish a reliable patient prole low risk, high risk, prohibitive risk to ensure that no individual is denied surgery while minimizing postoperative morbidity.
Most importantly, the appreciation of such considerations allows the surgeon and other members of the team anesthetist, intensivist to use a number of prophylactic measures intended to decrease morbidity in high-risk patients.
Where indicated, pulmonary rehabilitation, smoking cessation, optimization of medical treatment of chronic obstructive pulmonary disease, and treatment of cardiac disease decrease the risks associated with pulmonary or esophageal resection.
Although scoring systems are available to predict operative risk, numbers do not tell everything, and nothing replaces good clinical judgment. Moreover, none of those systems has been validated with large numbers of patients, and none provides insight into long-term outcomes such as QOL and cardiorespiratory function 5 years after surgery.
In this excellent chapter by Doctor Ferguson, a number of risk factors for operative morbidity and mortality are analyzed. In general, advanced age 70 years or older and comorbidities are intimately related and act as dependent variables in increasing the risk of postoperative events, especially in patients undergoing pneumonectomy or esophagectomy. Indeed, older patients are more likely to lose their ability to cooperate postoperatively increased risk of delirium , a feature that may add signicantly to the operative risk.
No patient should have pulmonary surgery, no matter how limited, without preoperative pulmonary function testing. In many cases, a simple spirometric test provides enough information to determine that the pulmonary function is normal and that the patient can tolerate pneumonectomy if necessary.
Exercise testing measurements. A PaCO2 that rises on minimal exercise, for example, is a strong indicator of inadequate reserve, and such patients must be looked at very carefully before surgery. Indeed, several authors have shown that exercise testing is the only objective measurement of cardiopulmonary reserve to demonstrate a statistically signicant difference between patients with benign postoperative courses and those with cardiorespiratory complications.
For most patients undergoing thoracotomy, the greatest cardiac risk arises from the presence of coronary artery disease. Similar risks have been identied for patients with angina. For these reasons, an accurate cardiac history and evaluation are of utmost importance. A screening exercise test is recommended for all patients who are smokers and older than 45 years of age, and for those with signicant other risk factors for coronary artery disease.
Overall, it is important to remember that, in the practice of thoracic surgery, technical misadventures do occur but seldom account for signicant postoperative morbidity. On the other hand, the majority. Ann Thorac Surg , Baldi S, Rufni E, Harari S, et al: Does lobectomy for lung cancer in patients with chronic obstructive pulmonary disease affect lung function?
A multicenter national study. J Thorac Cardiovasc Surg , Eur J Cardiothorac Surg , Bolliger CT, Guckel C, Engel H, et al: Prediction of functional reserves after lung resection: comparison between quantitative computed. Respiration , Cykert S, Kissling G, Hansen CJ: Patient preferences regarding possible outcomes of lung resection: What outcomes should preoperative evaluations target? Chest , N Engl J Med , Outcomes and quality of life before and after surgery. Sciurba Steve H. Salzman Key Points.
Other pulmonary function tests include maximal voluntary ventilation, maximal respiratory pressures, and lung compliance. Cardiopulmonary exercise testing not only delineates the reserve of each of the contributing subcomponents of the process of respiration but also allows us to integrate the effects of a myriad of measurable and unmeasurable system subcomponents to assess functional status through measurements of maximal power output and oxygen consumption.
The physiologic role of the lung is to maintain homeostasis of the arterial pH, PCO2, and PO2 under varying conditions of oxygen consumption and carbon dioxide production, a goal that is dependent on the lungs properties both as a mechanical structure and as a gas-exchanging surface. Clinical pulmonary function tests PFTs provide practical assessment of the integrity of the components of the respiratory system. Such testing provides a key ingredient in the diagnosis and assessment of severity of lung disease and is critical in the determination of perioperative risk.
Cardiopulmonary exercise testing CPET may offer further diagnostic and prognostic advantages over resting assessment of the respiratory system because it measures physiologic reserve and integrated functional capacity that can only be inferred from resting measurements.
It is imperative that the thoracic surgeon be competent not only in the application of lung function indices but also in the assessment of the techniques and quality of the data provided.
In this chapter we offer a practical approach to the assessment of lung function and exercise physiology. The role of these tests in preoperative risk assessment is discussed in Chapter 2.
Other indications are highlighted in Table PFTs, although essential to the proper assessment of the respiratory system, rarely provide a specic diagnosis in the absence of complementary clinical and radiographic data.
Tests of lung function can be broadly separated into those that evaluate the mechanical properties volumes, ows,.
Various lung diseases, or individual variation within a given disease, may result in discordant impairment between various mechanical properties or between mechanical and gas exchange properties. Thus, a combination of tests to evaluate lung mechanics and gas exchange will provide the most comprehensive understanding. This test measures the volume and ow rate of air that leaves the lungs how much and how fast. Traditionally, exhaled volume is measured as a function of time using a volume-displacement spirometer with ow rates calculated by dividing volume into timed segments.
It is now more common for systems to primarily measure ow, with real-time integration of ow over time to obtain volume, owing to the development of less expensive and more compact and accurate ow-sensing devices and fast microprocessors. The total volume exhaled from a full inspiration total lung capacity [TLC] to a full expiration residual volume [RV] is termed the vital capacity VC.
The maneuver can be performed using a forced complete exhalation, referred to as forced vital capacity FVC , or during a slow complete exhalation, dened as slow vital capacity SVC. Forced exhalation is necessary to assess expiratory ow rates, including peak expiratory ow PEF and the volume exhaled in the rst second FEV1 as well as other less commonly used timed volumes e. Slow vital capacity maneuvers are used to assess other static lung volumes and capacities such as inspiratory capacity IC and expiratory reserve volume ERV and, because spirometry cannot measure the air remaining in the lung after a complete exhalation, are often linked to tests of lung volume Fig.
A, Good duration of effort is seen on the volume-time curve by the plateau of volume change over time. In a normal ow-volume loop, good early effort is shown by the rapid upstroke to a slightly rounded sharp peak ow. Good duration of effort is illustrated by the upward concavity at the end of exhalation, indicating slowing of airow near residual volume. Patients with obstructive lung disease have deeper, upward concavity throughout exhalation on the ow-volume loop.
Objective assessment of pulmonary symptoms Documentation of abnormality Disability assessment Documentation of progression of disease Chronic obstructive pulmonary disease Neuromuscular disease Documentation of the patients response to therapy Asthma control Lung volume reduction surgery Sarcoidosis Preoperative assessment Lung cancer resection operability Nonthoracic surgery Timing of lung transplantation Screening for subclinical disease Emphysema in a tobacco smoker Occupational risk Diseases associated with pulmonary abnormalities.
Technique and Specic Methodology The forced maneuver consists of three distinct phases Miller et al, 1: 1. Maximal inspiration 2. A blast of exhalation 3. Continued complete exhalation to the end of test until no more air can be exhaled but maintaining an upright posture. It is then followed by a rapid inhalation back to full inspiration.
Enthusiastic coaching by the technician, including appropriate body language and phrases, is necessary to get full effort from the patient. The technician rst explains and demonstrates the technique, instructs the patient to inhale rapidly and completely with minimal pause at full inspiration only s , then instructs the subject to blast the air from the lung and keep going, keep going, keep going until the patient has fully exhaled. An unacceptable pause e. Patients can be standing or sitting during the test, and this is recorded on the report.
Sitting is generally preferred over standing for safety reasons because equivalent results are obtained in normal-weight individuals for either position. Obese subjects will frequently obtain a deeper inspiration in the standing position, resulting in higher expiratory volumes and ows Miller et al, b.
Acceptability and Repeatability Criteria Clinicians using parameters derived from these maneuvers need to become familiar with acceptable quality control standards, particularly when one is faced with deciding whether to utilize results provided from unfamiliar laboratories. In general, acceptable inspiratory and expiratory efforts are also reproducible. Ideally, both the FVL and V-t curve are reviewed when assessing test quality. The FVL graphs ow versus volume, resulting in relative expansion of the graphic data for the rst second, whereas the V-t curve gives equal spacing for each second and allows better resolution of the events marking the end of the test.
Coughing or glottic closure is more easily recognized on the FVL because the rapid transients of ow result in large up and down spikes in the curve Fig. Submaximal effort is recognized graphically on the FVL by a slow rise to the peak ow or by a rounding and broadening of the normal shape at the peak ow. Submaximal early effort, resulting in a slow upswing in the V-t curve, is. Eur Respir J , The spirometry standards have been met when three acceptable FVC efforts have been obtained, with the best and second best meeting between-maneuver acceptability criteria, also referred to as repeatiblilty Miller et al, a.
With the exceptions of maneuvers that contain a cough or glottic closure in the rst second or excessive volume of extrapolation, the use of data from maneuvers with poor repeatability or that fail to meet end-of-test criteria is left to the discretion of the interpreter Miller et al, a.
Final Report Data The report comments on the test quality, referring to the test components that were not reliable. A suboptimal test can be reported at the discretion of the interpreting physician in an appropriate clinical context as long as the report is specic in describing the likely direction and magnitude of errors Miller et al, a.
Other ow parameters come from this same curve. Two separate methodologies used to quantitate these volumesbody plethysmography and gas dilutionare discussed. Inspiratory reserve volume IRV is the maximum volume of gas that can be inhaled from the end-inspiratory level during tidal breathing. Residual volume RV refers to the volume of gas remaining in the lung after maximal exhalation regardless of the lung volume at which exhalation was started.
Expiratory reserve volume ERV is the volume of gas that can be maximally exhaled from the end-expiratory level during tidal breathing i. Vital capacity VC is the volume change at the mouth between the positions of full inspiration and complete expiration. Thoracic gas volume TGV or VTG , a term that still appears on many pulmonary function reports, is the absolute volume of gas in the thorax at any point and a term often used in body plethysmography when measuring FRC.
Body Plethysmography Plethysmographic techniques have become the gold standard for measurement of lung volumes. The patient sits in a large, air-tight, glass-enclosed box and breathes through a mouthpiece Fig. During the test an electronic shutter temporarily occludes the mouthpiece and the patient continues to pant against the closed shutter.
FRC is chosen as the starting point because the chest wall is in a relaxed state and it thus tends to be a very reproducible value. During an inspiratory pant against the closed airway the chest expands slightly, creating a negative pressure swing at the alveolus that can be measured at the mouth. Plethysmographic technique assumes that mouth and alveolar pressures are equal, whereas there is no ow as the subject pants against a closed shutter.
V is determined by applying Boyles law for a second time whereby the pressure change in the air-tight box Pbox is proportionate to the V of the chest wall. Intuitively, an individual with a small amount of air left in the lungs at end-expiration small FRC will have a higher mouth pressure change, when panting against a closed shutter, for a given change in thoracic volume reected in Pbox.
Mouth pressure Pm Change in mouth pressure Pm reflects change in alveolar pressure. In contrast, an individual with a large FRC will have a smaller mouth pressure change than a patient with a low FRC for a similar change in thoracic volume or Pbox.
Pitfalls in the measurement of lung volumes and its subcomponents related to improperly timed shutter closure are demonstrated in Figure Gas Dilution The helium dilution technique is a closed-circuit technique.
A spirometer is lled with a mixture of helium and oxygen. The amount of helium in the spirometer helium concentration C1 volume of spirometer [V1] is known at the beginning of the test. As the patient exhales to FRC, a valve switches the patient into a closed circuit breathing from the spirometer. Because the breathing circuit is closed assuming no leaks the total volume of helium in the system remains constant during the test. The total volume of nitrogen collected after complete washout is then in proportion to the FRC.
Technique and Specic Methodology In normal subjects, the same values for FRC and TLC will be obtained whether measured by gas dilution He dilution or N2 wash-out , plethysmography, or planimetry geometric measurement from a chest posteroanterior and lateral radiograph. On the other hand, gas dilution and wash-out techniques will underestimate FRC and therefore RV and TLC in patients who have severe inequality of the distribution of ventilation, such as those with severe airways disease.
Regions of lung with long-time constants directly proportional to resistance and compliance will equilibrate much more slowly than the length of a typical gas dilution test and so will not be seen by these techniques.
Conversely, plethysmographic techniques measure all intrathoracic gas, whether it communicates with the airways or not. Bullae are an extreme example of this poorly communicating lung. This difference between plethysmographic and gas dilution measurements of lung volume may have independent clinical meaning as trapped gas and has been shown to decrease after lung volume reduction surgery. Recent data indicate that FRC and therefore RV and TLC can be inaccurately overmeasured using plethysmographic techniques in patients with severe airow limitation.
In these cases, severe airow obstruction may result in phase. The SVC portion was well performed as demonstrated by the slowing of ow near full lung ination and near full exhalation demonstrating full inspiratory effort and full expiratory effort. The quiet tidal breathing portion left side of curve did not settle down a stable end-expiratory baseline for establishing FRC.
When the shutter closes in the body plethysmograph, the measurement of VLpleth thoracic gas volume during body box may be correct but the lack of a prior stable end-expiratory point to dene FRC will also result in incorrect values for FRC, and also ERV and IC, which are referenced to the point of FRC. Fortunately, this small error is in the direction that enhances the ability to recognize the underlying disease i.
As discussed earlier, plethysmographic measurements are combined with measurements derived from a VC maneuver, from which IC and ERV are also measured.
Combinations of the data from these two separate measurements are used to obtain the other lung volumes see Fig. A second recommended method, although not the preferred approach, utilizes a separate IC maneuver immediately after the FRC measurement to measure TLC.
This approach may be easier for some dyspneic patients. CO is so avidly bound to hemoglobin that, unlike oxygen, little back-pressure develops in the capillary to slow its transfer from alveolus to blood as a given volume of capillary blood makes its transit through the capillary bed.
CO is diffusion limited rather than perfusion limited and is thus ideal for assessing the lungs capacity to transfer gas. Consequently, its transfer is not dependent on cardiac output. It is dependent on the volume of the capillary bed exposed to alveolar surface and to the hemoglobin concentration because each increases the available mass of hemoglobin available for CO binding.
The transfer of CO also depends on the properties of the alveolar-capillary interstitium surface area and thickness. In addition, because little back-pressure of CO develops in the capillaries as a result of its transfer, the driving pressure for CO transfer can be measured from alveolar CO concentration alone without the measurement of blood CO except in the tobacco user. Technique and Specic Methodology The widely accepted technique used to measure DLCO, utilized in virtually all clinical laboratories, is the single-breath methodology, whereas historically, and still in research settings, other steady-state techniques are utilized.
In the singlebreath method, the subject exhales to RV and then rapidly inhales a gas mixture containing a minute concentration of CO commonly 0. After a second breath-hold at TLC, the patient rapidly exhales and, after a 0. Measurement of the initial inspired and nal concentration. To test maximal voluntary ventilation MVV the patient is instructed to breathe in and out as rapidly as possible for 12 seconds. The result is extrapolated to 1 minute and is expressed in liters per minute.
Disadvantages of this test are that results depend on motivation, and it is tiring for patients. In the past the MVV was recommended to assess respiratory muscle weakness; however, in general it has no advantages over VC. The mean of at least two acceptable tests that meet this repeatability requirement is reported.
No more than ve tests are performed because the resultant elevated carboxyhemoglobin COHb will affect the measurements. The absolute adjustment, and the adjustment per gram per deciliter of hemoglobin deviation from normal Maximal Respiratory Pressures The most specic tests to identify neuromuscular weakness as the cause of restriction are the maximal inspiratory pressure MIP and the maximal expiratory pressure MEP.
These parameters are also referred to as inspiratory pressure maximum PImax and expiratory pressure maximum PEmax. The MIP assesses the lowest pressure a patient can sustain for 1 to 2 seconds when inhaling from an occluded mouthpiece connected to a manometer Mueller maneuver.
The most negative pressure is obtained when the test is performed at or near RV because the diaphragm is at its longest precontraction length, the optimal position for force generation. Although simple tests, they are very effort dependent patient and tester.
A small leak is introduced to eliminate glottic and buccal occlusion and inadvertent measure of mouth pressures rather than intrathoracic pressures. Because of a learning curve, several trials are needed and careful instruction and encouragement are required. The reported value is the largest value that is reproducible and sustained for 1 second. Because they are very effortdependent tests, the MIP and MEP are better at ruling out respiratory muscle weakness than making a diagnosis. A low result may be due to lack of full effort.
MIP can be decreased in emphysema associated with lung hyperination and suboptimal respiratory muscle congurations. In this setting the low inspiratory pressures are independent of intrinsic muscle weakness. As such, measurements of MIP have been shown to improve after lung volume reduction surgery in concert with improvements in resting lung hyperination. Lung Compliance Although not a routine test in most laboratories, a more direct way of distinguishing parenchymal lung disease from chest wall disorders as a cause of restriction or low DLCO is to measure lung compliance.
These measurements require placement of esophageal balloon catheters to measure esophageal pressure, which reects pleural pressure across a compliant esophagus. Patients are asked to relax against a closed shutter attached to a manometer that measures mouth pressure at various lung volumes.
The difference between mouth and esophageal pressure represents the elastic recoil pressure of the lung, abbreviated PEL L. This low PEL L in chest wall restriction e. Assessment of Maximal Exercise Capacity In normal individuals and patients with cardiac abnormalities, exercise termination occurs at the maximal oxygen consumption VO2max due to overwhelming symptoms associated with metabolic demands at the limits of oxygen delivery and muscle oxidative capacity.
Another way of representing this value allows better recognition of the physiologic components that contribute to maximal oxygen delivery and oxygen extraction. The maximal values for each of these parameters depend on genetics, the level of conditioning, and the presence of disease. At rest, humans are capable of maintaining homeostasis under all but the most severe internal disease conditions or in the most extremes of physical environments, but abnormal reserves in any of the above physiologic attributes will commonly be exposed during exertion when the increased metabolic demands delineate the limits to the response.
VO2max is reported as a percentage of predicted normal or adjusted simply for weight in milliliters per kilogram per minute. Although there is considerable variability in the heart rate response to exertion in normal individuals, heart rate normally has a predictable slope relative to the increase in oxygen consumption see Fig.
At maximal exertion the normal heart rate response can be estimated simply as age in years. Increases in minute ventilation VE during exertion are necessary to maintain systemic blood gas and acid-base homeostasis. The formula describing the effect of changes in various factors on minute ventilation requirements is:. Compliance represents the slope of the pressure-volume curve. The level of minute ventilation required will depend on the central set point for PaCO2, which is inuenced by central drive, vagal afferents, and humoral input including pH and PaO2 , the CO2 production, and the dead space proportion.
Lactic acidosis associated with increasing exertion. The VE is commonly compared. This measure has been found to be a sensitive indicator of early disease, and dyspnea has been found to correlate closely with measurements of exercise EELV. The maneuver is based on the validated assumption that TLC, measured at rest, does not change during exertion. Improvement in dynamic hyperination has been documented after bronchodilator therapy and lung volume reduction surgery.
Impact of Exercise Protocol on Outcome It is important for laboratories performing exercise studies to understand the impact of variations in exercise protocol on exercise-derived indices. Author : F. Griffith Pearson,G. Pearson s Esophageal Surgery Author : F.
Griffith Pearson,Joel D. Chest Surgery Author : Hendrik C. Dienemann,Hans Hoffmann,Frank C. Pearson s Thoracic and Esophageal Surgery. Author : F. Pearson s Thoracic Esophageal Surgery Esophageal. Author : G. Pearson s Esophageal Surgery. Thoracic Surgery and Esophageal Surgery Package. Please see individual pages for full descriptions and contents of both titles: Thoracic Surgery 2e: Esophageal Surgery: Author : F.
Esophageal Surgery. Author : Joel D.
0コメント