|CURRICULUM ABSTRACT BIBLIOGRAFY|
Clinico-pathologic features of pulmonary emphysema include:
1. The reduction of the expiratory flow due to destruction of interalveolar septae, with attendant decrease of the elastic recoil and the alveolar expiratory driving pressure. In addition, there is a reduction of transmural pressure which is meant to maintain distal airways patency;
2. The pulmonary hyperinflation with air trapping, as a compensatory mechanism aimed at limiting the obstruction to the expiratory flow. Hyperinflation creates an increased end-expiratory positive pressure (PEEP) which, in turn, makes the inspiratory muscles operating at a disadvantageous length/tension relationship. Furthermore, the effort per single breath increases due to the reduced neuromechanical coupling, i.e., more nervous impulses need to be conducted to the osteomuscular structures to obtain the same muscular response and the same ventilatory capacity. The clinical counterpart is an increased dyspnea.3. The diaphragmatic flattening yields the shortening of the diaphragmatic fibers (mechanical disadvantage) and reduces the zone of apposition with the thoracoabdominal wall with a resulting diminished pressure gradient generated between the chest and the abdomen;
Typical x-ray in pulmonary emphysema
4. The dynamic hyperinflation with the auto-PEEP phenomenon resulting from the reduction of the expiratory time, especially with exercise. The ensuing dynamic hyperinflation creates a compression of the distal airways with an attendant increase of the work of breathing. The incomplete expiration of the emphysematous patient yields a further increase of intraalveolar PEEP and makes the inspiratory muscles operating at a worsened mechanical disadvantage;
5. The cardiovascular consequences, resulting from the hyperinflation and the auto-PEEP, are related to the increased pulmonary resistance, the reduced venous return to the right heart (mostly for the reduction or the inversion of the thoraco
abdominal pressure gradient), and, the ventilation-perfusion mismatch observed in these patients.
Preoperative work-up includes a careful history and physical examination, routine blood tests, inclusive of the alfa 1 antitrypsin titer, and, chest x-ray - in the postero-anterior and lateral views . Of additional contribution are a high definition computed tomographic evaluation of the chest (HRCT) and a ventilation/perfusion scintiscan which allow for the identification of the target areas to be surgically removed. The cardio-respiratory reserve is assessed through static and dynamic spirome
tric tests, the DLCO, the analysis of blood gases and the maximum oxygen consumption with exercise. The 6-minute walking test, the echo cardiogram and exercise stress test are needed to complete the functional evaluation. Similar importance is given to subjective measurements of the quality of life of the emphysematous patients, such as the dyspnea score.
Selection criteria are three-fold, namely, general criteria, anatomical, and functional. General criteria include patient's compliance to the rehabilitation program without psychological sequelae, smoking cessation dating six months prior to the operation, and less than 75 years of age. Anatomical criteria include the presence of a remarkable alveolar hyperinflation and of heterogeneous emphysema, i.e., emphysematous areas (target areas) irregularly distributed in the lung, interspersed with relatively normally appearing parenchyma.Functional criteria include an FEV1 less than 35% of predicted, an RV greater than 220%, a TLC greater than 120%, and, a DLCO less than 50% of predicted. Ideal candidates for this procedure should have a PaCO2<\<> 55 mmHg, and, a PaO2>55-60 mmHg. The latter can be obtained through oxygen-administration via nasal cannulas.
These patients should not have any cardiac disease possibly impairing the cardiovascular response, and, particularly, should not have pulmonary hypertension (PAP>35 mmHg). An acceptable candidate for LVRS should present an optimal nutritional (with a body weight ranging between 70 and 130% of predicted) and psychological profile. The latter is especially important being panick attacks among the most significant predictors of postoperative morbidity and poor postsurgical outcome. More recently, expanded indications for LVRS have included ventilator-dependent patients and patients with homogeneous emphysema or an associated
suspected lesion in the lung. The operative technique is aimed at resecting between 20% and 30% of each lung. The surgical approach may be through a median sternotomy, single or sequential anterior thoracotomies or through a mono or bilateral video-assisted thoracoscopies. Independent of the approach, which is basically surgeon's preference, LVRS can be conducted on both lungs in the same operative session, starting with the most compromised. One lung ventilation allows for the sequential exclusion of the two lungs and the intraoperative identification of the most diseased areas of the lung, which remain hyperinflated.
Top, a three-dimensional view image of a normal lung profusion. The image above shows the lungs of a patient with severe emphysema, with no profusions seen in the upper portions of both lungs. This strongly heterogeneous pattern of emphysema occurs in approximately 20 percent of patients with emphysema, and is the optimal pattern of emphysema for LVRS. Once introduced, the procedure generated a great deal of excitement in the medical community.
These target areas are resected with staplers reinforced by bovine pericardial or PTFE strips in order to seal the bites produced by of the staples on the diseased parenchyma. The potential for postoperative morbidity with prolonged hospitalization from persistent air leaks is substantial and will be discussed later. Centrolobular emphysema, commonly found in COPD patients, affects predominantly the upper lobes. Here, the line of resection on the peripheral lung is placed following the curvilinear contour of the lobes according to an upside-down U shape (Lung shaving, as LVRS was denominated at the beginning of this experience). Other pulmonary lobes, such as the middle and the lower lobes, may be involved by emphysematous changes as in panacinar emphysema, which is commonly found in patients with alfa1-antitrypsin deficiency. Postoperative care is focused on early extubation, chest tube removal, and, patient's mobilization. The latter is aimed at achieving muscle reconditioning which, in turn, may improve exercise tolerance.
Additional goals are weaning from oxygen therapy and reduction of steroid dependency, both to be obtained over a longer period of time. Postsurgical results are heterogeneous but, overall, converge in demonstrating an FEV1 improve
ment in the range of 50 to 60% compared to basal values at 30 months from the operation. This improvement is more remarkable if one considers only the first 12 months after LVRS, to slowly decline in time to the aforementioned rates. The beneficial effects of LVRS on lung hyperinflation are showed by the postoperative decrement of total lung capacity (TLC) and residual volume (RV). Likewise, exercise tolerance impro ves possibly because of the restora tion of the diaphragmatic geometric configuration and function. Accordingly, the thoraco-abdominal pressure gradient goes back to normal, thus augmenting the venous return to the right heart.
As far as oxygen dependency, it has been observed by some investigators that up to 68% of the patients were oxy
gen-free within 6 months of LVRS. A parallel decrease in steroid use was seen in 85% of the patients subjected to this procedure. More over, a definite improvement in terms of dyspnea and quality of life is commonly reported in most series. The operative mortality (i.e., deaths occurring within 30 days of operation) ranges between 4 and 10%. As previously stated, the most common complication is prolonged air leaks which are found in about 50% of the patients and cause delayed dismissal from the hospital. Other complica tions include pneumo nia, gastro intestinal bleeding, and, cardio vascular ac cidents.The varia bi lity of the selection criteria, operative indications, and postsur gical results reported in the li te ra ture make LVRS still an expe rimental procedure. More specifically, the type of relationship existing between LVRS and lung trans plantation, with the latter being restrained by donor shortage, side-effects of prolonged immunosup pression, elevated costs, and, 3-year survival rates of only 60%, needs to be determined. In this setting, it seems obvious that LVRS may represent a viable alter native to lung transplan tation. In light of cost containment policies, future efforts will be aimed at determining the precise encoding for this operation with the attendant reimbursement fee paid by govern ment organizations which serve as health care provider to the majority of the patients with advanced emphy sema.
Claude DeschampsSezione di Chirurgia Toracica Generale Mayo Clinic,
Divisione di Chirurgia Toracica A. O. "E. Morelli"
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