Anesthesia for Lung Resection: Preoperative Considerations

Anesthesia for Lung Resection

PREOPERATIVE CONSIDERATIONS

Lung resections are usually carried out for the diag-nosis and treatment of pulmonary tumors, and, less commonly, for complications of necrotizing pulmo-nary infections and bronchiectasis.

1. Tumors

Pulmonary tumors can be either benign or malig-nant, and, with the widespread use of bronchoscopic sampling, the diagnosis is usually available prior to surgery. Hamartomas account for 90% of benign pulmonary tumors; they are usually peripheral pul-monary lesions and represent disorganized normal pulmonary tissue. Bronchial adenomas are usually central pulmonary lesions that are typically benign, but occasionally may be locally invasive and rarely metastasize. These tumors include pulmonary car-cinoids, cylindromas, and mucoepidermoid adeno-mas. They often obstruct the bronchial lumen and cause recurrent pneumonia distal to the obstruction in the same area. Primary pulmonary carcinoids may secrete multiple hormones, including adrenocortico-tropic hormone (ACTH) and arginine vasopressin; however, manifestations of the carcinoid syndrome are uncommon and are more likely with metastases.Malignant pulmonary tumors are divided into small (“oat”) cell and non–small cell carcinomas.The latter group includes squamous cell (epider-moid) tumors, adenocarcinomas, and large cell (anaplastic) carcinomas. All types are more com-monly encountered in smokers, but more “never smokers” die of lung cancer each year in the United States than the total number of people who die of ovarian cancer. Epidermoid and small cell carcino-mas usually present as central masses with bronchial lesions; adenocarcinoma and large cell carcinomas are more typically peripheral lesions that often involve the pleura.

Clinical Manifestations

Symptoms may include cough, hemoptysis, wheez-ing, weight loss, productive sputum, dyspnea, or fever. Pleuritic chest pain or pleural effusion sug-gests pleural extension. Involvement of mediastinal structures is suggested by hoarseness that results from compression of the recurrent laryngeal nerve, Horner’s syndrome caused by involvement of the sympathetic chain, an elevated hemidiaphragm caused by compression of the phrenic nerve, dys-phagia caused by compression of the esophagus, or the superior vena cava syndrome caused by compression or invasion of the superior vena cava. Pericardial effusion or cardiomegaly suggests car-diac involvement. Extension of apical (superior sulcus) tumors can result in either shoulder or arm pain, or both, because of involvement of the C7–T2 roots of the brachial plexus (Pancoast syndrome). Distant metastases most commonly involve the brain, bone, liver, and adrenal glands.

Treatment

Surgery is the treatment of choice to reduce the tumor burden in nonmetastatic lung cancer. Various chemotherapy and radiation treatments are likewise employed, but there is wide variation among tis-sue types in their sensitivity to chemotherapy and radiation.

Resectability & Operability

Resectability is determined by the anatomic stage of the tumor, whereas operability is dependent on the interaction between the extent of the procedure required for cure and the physiological status of the patient. Anatomic staging is accomplished using chest radiography, computed tomography (CT) or magnetic resonance imaging (MRI), bronchoscopy, and (sometimes) mediastinoscopy. The extent of the surgery should maximize the chances for a cure but still allow for adequate residual pulmonary function postoperatively. Lobectomy via a posterior thora-cotomy, through the fifth or sixth intercostal space, or thorough video assisted thoracoscopic surgery (VATS), is the procedure of choice for most lesions. Segmental or wedge resections may be performed in patients with small peripheral lesions and poor pul-monary reserve. Pneumonectomy is necessary for curative treatment of lesions involving the left or right main bronchus or when the tumor extends toward the hilum. A sleeve resection may be employed for patients with proximal lesions and limited pulmonary reserve as an alternative to pneumonectomy; in such instances, the involved lobar bronchus, together with part of the right or left main bronchus, is resected, and the distal bronchus is reanastomosed to the proximal bronchus or the trachea. Sleeve pneumonectomy may be considered for tumors involving the trachea.

The incidence of pulmonary complications after thoracotomy and lung resection is about 30% and is related not only to the amount of lung tis-sue resected, but also to the disruption of chest wall mechanics due to the thoracotomy. Postoperative pulmonary dysfunction seems to be less after VATS than “open” thoracotomy. The mortality rate for pneumonectomy is generally more than twice that of for a lobectomy. Mortality is greater for right-sided than left-sided pneumonectomy, possibly because of greater loss of lung tissue.

Evaluation for Lung Resection

A comprehensive preoperative pulmonary assess-ment is necessary to assess the operative risk, minimize perioperative complications, and achieve better outcomes. Preoperative assessment of respi-ratory function includes determinations of respira-tory mechanics, gas exchange, and cardiorespiratory interaction.Respiratory mechanics are assessed by pulmo-nary function tests. Of these parameters, the most useful is the predicted postoperative forced expira-tory volume in one sec (FEV₁), which is calculated as follows:

Postoperative FEV₁ = preoperative FEV₁ × (1 – the percentage of functional lung tissue removed divided by 100)

Removal of extensively diseased lung (nonven-tilated but perfused) does not necessarily adversely affect pulmonary function and may actually improve oxygenation. Mortality and morbidity are signifi-cantly increased if postoperative FEV₁ is less than 40% of normative FEV₁, and patients with predicted postoperative FEV₁ of less than 30% may need post-operative mechanical ventilatory support.Gas exchange will sometimes be characterized by diffusion lung capacity for carbon monoxide (DLCO). DLCO correlates with the total function-ing surface area of the alveolar–capillary interface. Predictive postoperative DLCO can be calculated in the same fashion as postoperative FEV₁. A predicted postoperative DLCO of less than 40% also corre-lates with increased postoperative respiratory and cardiac complications. Adequacy of gas exchange is more commonly assessed by arterialblood gas data such as Pao2 >60 mm Hg and· a Pa·co2 <45 mm Hg.

Ventilation-perfusion(V/Q)scintigraphy pro-vides the relative contribution of each lobe to over-all pulmonary function and may further refine the assessment of predicted postoperative lung function, in patients where pneumonectomy is the indicated surgical procedure and there is concern whether a single lung will be adequate to support life.

Patients considered at greater risk of periop-erative complications based on standard spirometry testing and calculation of postoperative function should undergo exercise testing for evaluation of

cardiopulmonary interaction. Stair climbing is the easiest way to assess exercise capacity and cardio-pulmonary reserve. Patients capable of climbing two or three flights of stairs have decreased mortal-ity and morbidity. On the other hand, the ability to climb less than two flights of stairs is associated with increased perioperative risk. The gold standard for evaluating cardiopulmonary interaction is by labo-ratory exercise testing and measurement of maximal minute oxygen consumption. A V˙o₂>20 mL/kg is not associated with a significant increase in peri-operative mortality or morbidity, whereas a minute consumption of less than 10 mL/kg is associated with an increased perioperative risk.

A combination of tests to evaluate the three components of the respiratory function (ie, respira-tory mechanics, gas exchange, and cardiopulmonary interaction) has been summarized in the so-called “three-legged” stool of respiratory assessment (Figure25–10).

2. Infection

Pulmonary infections may present as a solitary nod-ule or cavitary lesion (necrotizing pneumonitis). An exploratory thoracotomy may be carried out to exclude malignancy and diagnose the infectious agent. Lung resection is also indicated for cavitary lesions that are refractory to antibiotic treatment, are associated with refractory empyema, or result inmassive hemoptysis. Responsible organisms include both bacteria and fungi.

3. Bronchiectasis

Bronchiectasis is a permanent dilation of bronchi. It is usually the end result of severe or recurrent inflammation and obstruction of bronchi. Causes include a variety of viral, bacterial, and fungal patho-gens, as well as inhalation of toxic gases, aspiration of gastric acid, and defective mucociliary clearance (cystic fibrosis and disorders of ciliary dysfunction). Bronchial muscle and elastic tissue are typically replaced by very vascular fibrous tissue. The lat-ter predisposes to bouts of hemoptysis. Pulmonary resection is usually indicated for massive hemopty-sis when conservative measures have failed and the disease is localized. Patients with diffuse bronchiec-tasis have a chronic obstructive ventilatory defect.