Thoracic Anesthesia

PART 1

The Principles of Thoracic Anesthesia


CHAPTERS


8
Anatomy, Imaging and Practical Management of Selected Thoracic Surgical Procedures

Betty C. Tong
Thomas A. D’Amico

ANATOMY

Chest Wall and Surface Anatomy

The thoracic viscera are protected by the chest wall and sternum. The bony framework of the chest wall is composed of 12 thoracic vertebrae, intervertebral discs, 12 pairs of ribs with corresponding cartilages, and the sternum. The thoracic vertebrae and intervertebral discs are positioned in the posterior midline; the spinous processes are relatively easy to identify as landmarks. The scapula overlies a portion of the first seven pairs of ribs posteriorly. With the arm abducted, the (vertebral) medial border of the scapula is parallel to the oblique fissure of the underlying lung.1

The sternum lies in the anterior midline and has three components: manubrium, body, and xiphoid process. The sternal notch, or superior border of the manubrium, is easily located between the clavicular heads. The junction of the manubrium and body of the sternum is called the sternal angle, or angle of Louis. This is an important landmark, corresponding to the level where the second costal cartilages articulate with the sternum. Since the first rib may be partially or completely obscured by the clavicle, accurate counting of ribs may commence at the sternal angle. This landmark is also important for deeper thoracic structures, marking the level of the tracheal bifurcation (carina) as well as the aortic arch.2

The upper seven pairs of ribs are considered to be true ribs because they form a complete circle between the sternum and vertebrae. The costal cartilages connect the ribs to the sternum anteriorly. In contrast to those of the first seven pairs of ribs, the costal cartilages of the 8th, 9th, and 10th ribs attach to the cartilage of the preceding rib. The 10th costal cartilage marks the most inferior point of the costal margin.1 Aside from their vertebral attachments, the 11th and 12th ribs do not have other skeletal attachments and are considered to be “floating ribs.”

The blood supply to the chest wall comes from the subclavian artery and aorta. The subclavian artery gives rise to the internal thoracic artery, also known as the internal mammary artery, as well as the first two intercostal arteries. Together, these vessels supply the anterior chest wall. The lateral and posterior areas of the chest wall are supplied by the remaining intercostal arteries, which arise as direct branches from the aorta posteriorly. Importantly, the intercostal bundle, consisting of the intercostal artery, vein and nerve, runs along the inferior aspect of each rib and is subject to injury during procedures such as thoracotomy or even thoracostomy tube placement.

The extrathoracic muscles of the chest wall provide both anatomic landmarks as well as substrate for surgical reconstruction of chest wall defects. The latissimus dorsi provides a large and versatile myocutaneous flap. Supplied by the thoracodorsal artery, nerve and vein, it is used most frequently for reconstruction of anterior and lateral chest wall defects. The pectoralis major is often used for anterior and midline chest wall defects, and is especially useful for coverage of sternal wounds. The rectus abdominus, external oblique and trapezius muscles may also be used for reconstruction of chest wall defects. When intrathoracic muscle flaps are needed (eg, coverage of bronchial stumps, filling a post-pneumonectomy space), the intercostal muscles and serratus anterior muscle are most frequently utilized.

AIRWAY AND LUNGS

Trachea

The trachea, palpable in the anterior neck, enters the chest just posterior to the manubrium and serves as the ventilatory conduit between the larynx and mainstem bronchi. It spans from the inferior border of the cricoid cartilage, the only complete cartilaginous ring in the airway, to the carina. There, the airway divides into the right and left mainstem bronchi. The trachea is comprised of 14 to 19 C-shaped incomplete cartilaginous rings and elastic membranous tissue.3 During childhood, the cross-sectional area of the trachea is circular. With growth and development, it becomes elliptical in shape with its transverse length slightly longer than the anteroposterior length. However, normal anatomic variation among adults occurs frequently, and includes both circular and triangular cross-sectional shapes.4 The average tracheal length in an adult ranges from 10 to 15 cm; in general, tracheal dimensions are slightly larger in men than women.

The posterior membranous trachea is composed of smooth muscle and respiratory epithelium, with ciliated pseudostratified columnar epithelium and mucus-producing goblet cells. The intercartilaginous tissue between the tracheal rings also contains muscle. It is this muscular tissue that is responsible for dynamic changes in tracheal size and luminal diameter.

The blood supply to the trachea is segmental, and closely related to that of the esophagus. The inferior thyroid artery arises from the thyrocervical trunk of the subclavian artery and supplies blood to both the proximal trachea and esophagus. Branches of the bronchial arteries, which arise directly from the aorta, supply the lower trachea, carina and bronchi. These arterial branches enter the tracheoesophageal groove and further divide into primary tracheal and esophageal branches. The primary tracheal branches further divide into lateral longitudinal vessels, which join together and run parallel to the longitudinal axis of the trachea, and transverse intercartilaginous arteries, which supply blood in a circumferential manner. Extensive circumferential dissection of the trachea and airways is to be avoided in order to prevent bronchial stump dehiscence or anastomotic disruption.

Bronchopulmonary Anatomy

At the carina, the trachea divides into the right and left mainstem bronchi. The lungs are divided into lobes and segments. The first branch off the right main bronchus is the right upper lobe bronchus. The ongoing airway, called bronchus intermedius, then divides into the right middle and lower lobe bronchi. The three lobes of the right lung are further divided into 10 segments (Table 8–1). The right upper lobe bronchus gives rise to the apical, anterior and posterior segments, while the right middle lobe contains the medial and lateral segments. The right lower lobe is composed of the superior segment and four basilar segments: anterior, posterior, medial and lateral.

Table 8–1. Lobar and Segmental Anatomy of the Lungs

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The left lung is slightly smaller than the right lung, and has only two lobes (upper and lower) and eight segments. The lingula, the inferior portion of the left upper lobe, is anatomically analogous to the right middle lobe. From the carina, the left main bronchus gives rise to the left upper and lower lobe bronchi. The left upper lobe contains the apicoposterior and anterior segments in addition to the superior and inferior lingular segments. The left lower lobe is comprised of the superior segment, in addition to three basilar segments: anteromedial, lateral, and posterior.

The arterial blood supply to the lungs follows the segmental bronchial anatomy. The main pulmonary artery arises from the heart and divides into the left and right pulmonary artery trunks. Branches of the right main pulmonary artery include the truncus arteriosus and posterior ascending artery, which supply the right upper lobe. The right middle lobe branch supplies its namesake, and the right lower lobe is supplied by a superior segmental artery branch as well as by branches of the basilar trunk. Similarly, the left main pulmonary artery gives rise to apical, anterior, posterior and lingular branches, which supply the left upper lobe. The superior segmental artery and common basal trunk supply the left lower lobe.

Paired pulmonary veins, superior and inferior, provide venous drainage from the lungs to the right atrium of the heart. The right superior pulmonary vein drains the right upper and middle lobes, and the right inferior pulmonary vein drains the right lower lobe. Similarly, on the left side, the superior pulmonary vein drains blood from the left upper lobe and the inferior pulmonary vein drains the left lower lobe. Rarely do the pulmonary vein branches join to form a single vessel or “common vein.” However, this must be recognized during pulmonary resection in order to avoid division of the entire venous drainage from the lung, which would necessitate pneumonectomy.

ESOPHAGUS

The esophagus serves as a conduit for food and drink between the hypopharynx and stomach, and traverses three anatomic regions: the neck, thorax, and abdomen. The cervical esophagus measures approximately 5 cm in length and is located between the trachea and vertebral column. Proximally, the esophagus begins in the neck at the cricopharyngeus, or upper esophageal sphincter. Of the three areas of normal anatomic narrowing of the esophagus, the cricopharyngeus is narrowest and the most common site of iatrogenic perforation. Upon swallowing, the cricopharyngeus relaxes to accommodate the bolus traveling from the pharynx to the esophagus. The right and left recurrent laryngeal nerves reside in their respective tracheo-esophageal grooves and are at risk for injury during dissection of either the trachea or esophagus in this region.

The thoracic esophagus measures approximately 20 cm in length. From its entry at the thoracic inlet to the tracheal bifurcation, the esophagus maintains its close anatomic relationship with the posterior tracheal wall and the prevertebral fascia. Another area of normal anatomic narrowing occurs at the level of the aortic arch, where an indentation in the left lateral esophageal wall is often seen on both endoscopic examination and contrast esophagography. From this point on, the esophagus continues anterior and often slightly left of the vertebral column until it reaches the diaphragmatic hiatus, the third site of normal anatomic narrowing.

The abdominal portion of the esophagus measures 1.25 to 2 cm in length and includes part of the lower esophageal sphincter. As the esophagus traverses the diaphragmatic hiatus, it is surrounded by the phrenoesophageal membrane, a fibroelastic ligament arising from the subdiaphragmatic fascia as a continuation of the transversalis fascia of the abdomen. The lower limit of this membrane blends with the serosa of the stomach; a prominent anterior fat pad marks its end, which also marks the approximate location of the gastroesophageal junction.

The blood supply to the esophagus varies by anatomic location. Branches of the inferior thyroid artery are responsible for blood supply to the cervical esophagus. Bronchial arteries supply the thoracic esophagus. Approximately 75% of individuals have one right-sided and one- or two left-sided branches, which arise directly from the aorta. The abdominal portion of the esophagus receives arterial blood supply from branches of the inferior phrenic and left gastric arteries. One unique feature of the esophagus is the extensive collateral network of vessels in the muscular and submucosal layers. Upon entry to the esophageal wall, the arteries divide to form longitudinal anastomoses. As a result, the esophagus can undergo extensive mobilization with nominal risk of devascularization or ischemic necrosis.

Venous drainage of the esophagus occurs through a submucosal venous plexus, which then flows into a periesophageal venous plexus. The esophageal veins originate from the periesophageal venous plexus. Further drainage of the esophageal veins varies by region: in the neck, the esophageal veins drain into the inferior thyroid vein; in the thorax, esophageal veins drain into the bronchial, hemiazygos and azygos veins; and in the abdomen, drainage is into the coronary vein.

MEDIASTINUM

The mediastinum is the area of the thorax that resides between the pleural spaces, extending from the thoracic inlet to the diaphragm. It is divided into the superior and inferior mediastinum by a plane passing through the sternal angle and the fourth thoracic vertebra. There are three anatomic subdivisions of the inferior mediastinal space: anterior, middle, and posterior. The anterior mediastinum contains the internal mammary arteries and veins, lymph nodes, thymus gland, connective tissue and fat. Ectopic parathyroid or thyroid gland tissue may also be found in the anterior mediastinal compartment.

The middle mediastinum is also called the visceral compartment. It contains the pericardium, heart, great vessels, trachea and proximal mainstem bronchi, and esophagus. In addition, lymphatics, the right and left vagus and phrenic nerves, thoracic duct, connective tissue and fat are also contained within the middle mediastinum.

The posterior mediastinum includes the paravertebral sulci, or potential spaces located along each side of the vertebral column. Neurogenic structures such as the ventral ramus, thoracic spinal ganglia, and sympathetic trunk are found in the paravertebral sulci. The proximal portions of the intercostal arteries and veins, connective tissue and lymphatics are also located within the posterior mediastinum.

DIAGNOSTIC IMAGING MODALITIES

Imaging of the Lungs

Several different imaging modalities are used in the evaluation of pulmonary disorders. Plain chest radiography, done in the primary care or emergency room setting, often provides the first indication of pulmonary pathology. A standard chest radiograph consists of two images: one taken in the posterioranterior (PA) projection and the other from the left lateral erect position (Figure 8–1). These images provide visualization of the pulmonary parenchyma, mediastinum, bony structures and diaphragm. Lateral decubitus films are often employed to evaluate the mobility of pleural effusions seen on plain films.

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Figure 8–1. PA and lateral chest x-ray demonstrating left-sided pleural effusion. The presence of sternal wires indicates prior median sternotomy.

Computed tomography (CT) studies provide excellent anatomic detail and characterization of abnormalities or lesions detected on plain radiographs of the chest. Important features that may raise or lower the suspicion of malignancy include the following: location, appearance (cavitary vs solid, spiculated vs well-defined), involvement of adjacent structures such as chest wall or great vessels. Enlarged mediastinal lymph nodes (> 1 cm in long axis) may suggest the presence of metastatic disease and therefore warrant further evaluation. CT may also provide additional information regarding mediastinal or hilar lymphadenopathy, chest wall lesions, and diseases of the lung parenchyma such as bronchiectasis or pulmonary fibrosis (Figure 8–2). Currently, contrast-enhanced CT angiography is widely used for diagnosis of acute pulmonary embolism. With a sensitivity over 80%, it has advantages over traditional ventilation-perfusion scans, including speed, detection of venous thrombosis, and characterization of nonvascular structures.5 However, patients with impaired renal function may not be candidates for use of intravenous contrast and in these cases, the ventilation-perfusion scan may be preferred.

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Figure 8–2. A. Diffuse mediastinal adenopathy demonstrated on chest CT. B. CT with coronal reconstruction demonstrating pleural thickening consistent with mesothelioma. C. Bone windows of CT scan demonstrating a lesion of the right 3rd rib (arrow). D. Non-contrast CT scan of the chest demonstrating thymic mass in anterior mediastinum (arrow). E. CT scan of the chest demonstrating the presence of left-sided giant bullous disease.

In addition to CT, positron emission tomography (PET) imaging is very useful in further characterizing potentially malignant lesions. The technique uses a radiolabeled glucose (18-fluorodeoxyglucose [18FDG]) to identify tissues with increased metabolic activity, such as malignant or infectious processes. In a recent meta-analysis, the sensitivity of18FDG-PET for identifying malignant lesions was 96.8% and the specificity was 77.8%.6 However, one limitation of PET is that its resolution is limited in tumors less than 1 cm in size, and accuracy is decreased in these smaller lesions.7

Integrated PET/CT (Figure 8–3) and PET/CT fusion (Figure 8–4) studies combine the advantages of both modalities, providing excellent anatomic detail in addition to information regarding metabolic activity. As compared to PET alone and CT alone, integrated and fusion PET/CT studies have greater sensitivity, specificity, negative predictive value and overall accuracy for staging of mediastinal lymph nodes.8,9 PET/CT can also be used for re-staging of the mediastinal lymph nodes following neoadjuvant therapy; however, the sensitivity of both standalone PET and integrated PET/CT are both lower after induction therapy.10

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Figure 8–3. A. Left lower lobe lesion demonstrated on CT images. B. PET images of left lower lobe mass (arrow). C. Integrated PET/CT images of hypermetabolic left lower lobe mass.

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Figure 8–4. PET/CT fusion of hypermetabolic left hilar mass.

For evaluation of suspected superior sulcus (Pancoast) tumors, MRI is often used and preferred. It is superior to CT for evaluating tumor involvement of the brachial plexus, subclavian vessels and vertebral bodies.11 Involvement of these structures may alter surgical management or even render the patient unresectable, thereby changing the course of recommended therapy.

The ventilation-perfusion (V/Q) scan has several uses. Historically, it was most often used in the diagnostic evaluation of suspected pulmonary embolus. More recently, however, CT angiography has supplanted the V/Q scan for patients with suspected pulmonary embolus. Nevertheless, the quantitative V/Q scan is often used to estimate the contribution of the upper, middle, and lower lung zones to overall lung perfusion. Patients with marginal pulmonary function may be able to tolerate resection of a lobe or segment in which there is nominal perfusion as demonstrated by the quantitative V/Q scan.

Imaging of the Mediastinum

The plain chest radiograph is often the most common initial diagnostic imaging study for mediastinal abnormalities. The posteroanterior and lateral radiograph can reveal the presence of a mediastinal mass and its location (anterior vs posterior), as well as mediastinal widening. Further evaluation is usually done with CT imaging, which provides excellent anatomic detail with regard to size and location as well as proximity to and involvement of surrounding structures and great vessels. At present, CT angiography is the test of choice for imaging the great vessels in a hemodynamically stable patient with suspected aortic dissection. In a recent study comparing helical CT and surgical findings, CT demonstrated 100% accuracy in diagnosing Type A aortic dissections and intramural hematomas.12 For hemodynamically unstable patients, however, transesophageal echocardiography is preferred. MRI, while not used routinely, may provide improved characterization of soft tissues relative to CT and may also be used to characterize vascular structures without the need for intravenous contrast.

Esophageal Diagnostic Modalities

Barium swallow (Figure 8–5) is often one of the first tests done when esophageal pathology is suspected. Usually done under videofluoroscopy, the patient swallows a bolus of radio-opaque barium, which opacifies the esophageal lumen during its transit to the stomach. With this technique, abnormal esophageal motility as well as structural changes in the esophageal lumen (eg, strictures, masses, filling defects) can be observed.

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Figure 8–5. Barium swallow demonstrating tortuous esophagus with distal bird’s beak deformity consistent with achalasia.

CT is also useful for evaluating the esophagus. The presence of paraesophageal fat helps to distinguish the normal esophagus from surrounding vessels, airway and other structures. Hiatal hernias, esophageal tumors, and even esophageal perforation may be diagnosed using contrast-enhanced CT.

As with other malignancies, PET and PET/CT are frequently used and recommended for the staging evaluation of esophageal cancer. While PET has a sensitivity of 91% to 95% for detecting primary esophageal tumors, accurate T staging is sometimes difficult.13 Similarly, the sensitivity and specificity of standalone PET for detecting locoregional lymph node involvement in esophageal cancer are 51% and 84%, respectively.14 However, PET and PET/CT are most useful for determining the presence of distant metastases.15 The presence of distant metastatic disease may, in turn, change the clinicians’ management strategy, as these patients are not candidates for surgical resection.

Endoscopic ultrasound (EUS) combines high-frequency ultrasonography with endoscopy, and is highly accurate in the locoregional staging of esophageal cancer. With the ultrasound probe, five layers of the esophagus are identified: superficial mucosa, deep mucosa, submucosa, muscularis propria and adventitia. The accuracy of predicting the depth of tumor penetration, or T stage, is approximately 85% to 90%.16 Similarly, EUS is used for evaluation of regional lymph nodes, with a sensitivity of 73% and specificity of 77% for predicting the pathologic status of regional lymph nodes.17 Characteristics of malignant lymph nodes include hypoechoic or homogeneous appearance, round shape, sharply demarcated borders, size > 1 cm and solitary appearance.18-20 Fine needle aspiration of suspicious lymph nodes or liver lesions can be performed through the EUS probe to aid in staging accuracy.

PRACTICAL MANAGEMENT OF THORACIC SURGICAL PROCEDURES

General Guidelines

The complete preoperative evaluation of the thoracic surgery patient is discussed in detail in Chapter 9. For patients proceeding to surgery, several general principles are relevant for the intraoperative management of the thoracic surgical patient. First, one-lung ventilation is preferred for the vast majority of thoracic procedures, including all types of lung resection as well as esophageal surgery. Lung isolation with ventilation of the nonoperative side provides room in the thoracic cavity for the surgeon to work and facilitates performance of the operation. In addition, for cases involving massive hemoptysis or bronchopleural fistula, lung isolation can help to prevent contamination of the noninvolved side by the contralateral lung. Several methods can be used to isolate the lungs: double-lumen endotracheal tubes, bronchial blockers placed through a single-lumen endotracheal tube, and selective intubation of the right or left mainstem bronchus using a single-lumen endotracheal tube. Specific techniques for placement of these tubes and devices are discussed in Chapters 5 and 22. For the minority of patients who cannot tolerate single lung isolation, some procedures may be done with short periods of apnea and both lungs otherwise ventilated.

Patients who have had previous chemotherapy and/or radiation therapy merit special anesthetic consideration. Several chemotherapeutic agents, including those routinely used to treat lung and esophageal cancer, have been associated with pulmonary toxicity and are listed in Table 8–2. Bleomycin, most often used for patients with germ cell tumors and lymphoma, is the most studied. Oxygen administration is a recognized risk factor for bleomycin-induced pneumonitis; other risk factors include age, smoking, renal dysfunction, and history of mediastinal radiation.21 Currently, there is no documented “safe” FiO2 level for patients with a history of bleomycin exposure; thus, the lowest possible FiO2 that enables the anesthesiologist to adequately oxygenate the patient is desired. Similarly, patients who have undergone mediastinal or chest radiotherapy are at risk for developing radiation pneumonitis. In lung cancer patients, the incidence of radiation pneumonitis is 5% to 15%; the proportion of breast cancer and Hodgkin’s lymphoma patients who develop radiation pneumonitis is lower.21,22 The risk of radiation pneumonitis may be increased with concomitant administration of chemotherapy, previous irradiation, total radiation dose and number of daily fractions, and recent withdrawal of steroids. Again, adequate oxygenation with the lowest possible FiO2 is preferable for these patients.

Table 8–2. Chemotherapeutic Agents Associated with Pulmonary Toxicity

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Most thoracic surgical resections can be accomplished with two large bore peripheral intravenous lines and arterial line monitoring. However, central access may be desirable for cases such as standard pneumonectomy, extrapleural pneumonectomy, and resection of mediastinal tumors. If a central line is to be placed for administration of fluids and/or central venous monitoring, it should be placed on the ipsilateral side of the planned resection. In addition, for patients with complex mediastinal tumors who may require resection and reconstruction of the superior vena cava, preoperative placement of a femoral central venous line is advised.

The majority of lung resections and esophageal operations are conducted with the patient in the lateral decubitus position. Following the induction of general anesthesia and intubation, the patient is turned to the lateral decubitus position and secured to the operating table with ample padding under pressure points. Potential neurovascular injuries resulting from improper attention to the lateral decubitus position warrant discussion. The brachial plexus of the dependent arm is subject to compression injury if there is inadequate padding under the dependent thorax. Careful placement of this padding is of the utmost importance, as migration into the axilla can also result in injury. The use of the bean bag has improved the ability both to stabilize the patient and to protect the axilla and the brachial plexus. The nondependent arm is also subject to brachial plexus injury; this is usually a stretch injury caused by excessive abduction of the nondependent arm, or lateral bending of the cervical spine.23 Table 8–3 lists other patient positions and incisions for common thoracic surgical procedures.

Table 8–3. Common Patient Positions and Associated Thoracic Surgical Procedures

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Prevention of deep venous thrombosis (DVT) and subsequent pulmonary embolism begins in the operating room. Nearly all patients undergoing thoracic surgical procedures should be provided with measures to prevent perioperative DVT. The incidence of DVT following pulmonary resection increases with the extent of resection and ranges from 7.4% to 14% for patients undergoing pneumonectomy.24,25 Intraoperative DVT prophylaxis usually includes intermittent calf compression with compression stockings and/or sequential compression devices (SCDs). Postoperative DVT prophylaxis includes compression stockings and SCDs in addition to the subcutaneous administration of unfractionated or low-molecular weight heparin.

Judicious fluid management is also extremely important in thoracic surgery, especially with one-lung ventilation. The incidence of acute lung injury (ALI) and adult respiratory distress syndrome (ARDS) is approximately 1% following lobectomy and 2% to 4% following pneumonectomy.26 However, respiratory complications account for the majority of mortalities following lung resection.27 With excessive administration of intravenous fluids, increased shunting can occur, leading to pulmonary edema of the dependent lung. Increasing perioperative fluid administration has been identified as an independent risk factor for lung injury following lung resection.28 General guidelines also dictate that crystalloid administration does not exceed 3 L in the first 24 hours for an average adult patient; it is not necessary to ensure a urine output of > 0.5 mg/kg/h; and no fluids should be administered for “third space” losses during pulmonary resection.23 If greater tissue perfusion is desired, invasive monitoring and administration of inotropes or vasopressors should be considered rather than additional intravenous fluid administration.

One specific intraoperative condition deserves mention here. With the patient in the lateral decubitus position, the acute onset of hypotension, hypoxia and high airway pressures can herald the onset of a spontaneous pneumothorax in the “down” or ventilated lung. This condition must be recognized and remedied quickly. Treatment includes the immediate return to dual-lung ventilation and placement of a thoracostomy tube into the nonoperative side to evacuate the pneumothorax. Temporary evacuation of the pneumothorax may be achieved intraoperatively by opening the contralateral pleura, either anterior to the pericardium or just anterior to the esophagus and aorta at the level of the inferior pulmonary ligament. Detection of a downside tension pneumothorax is facilitated by routine use of an esophageal stethoscope (see Chapter 13).

Maintaining normothermia can also be a challenge during thoracic surgery. However, hypothermia inhibits many of the body’s normal physiologic functions, and must be avoided intraoperatively. Techniques to prevent hypothermia include use of patient warming devices, increasing the ambient room temperature, and use of fluid warmers.

Effective perioperative analgesia is mandatory for all patients undergoing lung resection, regardless of operative approach. For patients undergoing lung resection, thoracic epidural analgesia has been associated with decreased risk of postoperative pulmonary complications as well as decreased odds of postoperative death.29,30 This is due to increased mean lung volumes resulting from improved respiratory mechanics and increased activity levels, which are effective in decreasing postoperative pulmonary complications.31

Selected Thoracic Surgical Procedures

MEDIASTINOSCOPY (SEE ALSO CHAPTER 10)

Mediastinoscopy is most often used for surgical staging of the mediastinal lymph nodes in patients with non-small cell lung cancer (NSCLC). It can also be used to obtain tissue diagnosis in patients with anterior mediastinal masses, such as lymphoma. Mediastinoscopy and associated procedures are discussed in detail in Chapter 10. In the procedure, a 1.5 to 2 cm low transverse cervical incision is made and the soft tissues are dissected to the trachea. The pretracheal fascial plane is dissected, and the mediastinoscope is inserted to facilitate biopsy of the mediastinal lymph nodes. While the overall complication rate from this procedure is only 1.07% in recent published series, both surgeon and anesthesiologist must be prepared for potential life-threatening complications such as major hemorrhage from injury to the great vessels (0.32% incidence).32 Other potential complications from mediastinoscopy include vocal cord dysfunction due to injury of the recurrent laryngeal nerve, tracheal injury and pneumothorax.

For the procedure, only a single-lumen endotracheal tube is necessary. Standard monitoring includes pulse oximetry and blood pressure monitoring via a right radial arterial line. The right side is preferred because inadvertent compression of the innominate artery, which supplies the right common carotid and right subclavian arteries, can occur during the procedure. Patients with few cerebral collaterals may experience ischemia if this is not detected.

If severe hemorrhage is encountered, a number of maneuvers should be performed immediately. The surgeon should pack the wound to allow for hemodynamic stabilization as well as to potentially tamponade the bleeding source. Large-bore intravenous access should be obtained, if not done so already. In addition, blood products should be made immediately available to the anesthesiologist; blood and fluid warmers and infusers should also be brought into the operating room for use. If time permits and the surgeon believes that thoracotomy is indicated for repair of the injury, lung isolation should be obtained either using a bronchial blocker or exchange of endotracheal tubes to a double lumen tube. Once the patient has achieved hemodynamic stability, the cervical wound can potentially be re-explored; however, another approach (thoracotomy or sternotomy) to identify and repair the injury is likely more prudent.

PULMONARY RESECTION (SEE ALSO CHAPTER 13)

The most frequent indications for pulmonary resection are documented malignancy, either primary lung cancer or metastasis from an extrapulmonary site, and solitary pulmonary nodule with suspicion of primary lung cancer. Regardless of incision or approach, several oncologic principles dictate the extent of resection for lung cancer. First, the tumor should be completely resected with negative operative margins. For tumors involving the chest wall, diaphragm or other resectable surrounding structures, en bloc resection should be completed without tumor spillage. In addition to resection of the primary tumor, mediastinal lymph node sampling or dissection is done to ensure accurate pathologic staging.

Anesthetic management for patients undergoing pulmonary resection is discussed in detail in Chapter 13. In general, intraoperative management includes standard monitoring, large bore intravenous access and an arterial line. As discussed, one-lung ventilation is preferred for all pulmonary resections. For any thoracoscopic procedure, a tidal volume less than 300 cc is preferred, as higher tidal volumes can result in excessive movement of the mediastinum, which can make the surgical dissection more difficult. Patients should be kept normothermic and normotensive throughout the procedure. Ideally, all patients undergoing pulmonary resection are extubated and spontaneously breathing in the operating room prior to transfer to the postanesthesia care unit.

SUBLOBAR RESECTIONS: WEDGE RESECTION AND SEGMENTECTOMY

A wedge resection is a nonanatomic resection most often used for metastasectomy or for diagnostic purposes. It involves resection of the nodule or other focal abnormality with a margin of surrounding normal lung tissue. Segmentectomy requires anatomic dissection of one or more bronchopulmonary segments and separate division of the associated arterial and venous blood supply. This approach is most often used for management of patients who have small primary lung cancers but do not have the physiologic reserve to tolerate a lobectomy. For management of lung cancer, one advantage of segmentectomy over wedge resection is that the anatomic dissection also includes the associated lymphatics, which is desirable from an oncologic standpoint.

LOBECTOMY

The most common and standard operation for a primary lung cancer is lobectomy, an anatomic resection in which the lobar bronchus, pulmonary artery branches and pulmonary vein branch(es) are individually dissected and divided. This operation has been the mainstay of lung cancer resection since 1995, when the Lung Cancer Study Group compared limited resection (either wedge resection or segmentectomy) to lobectomy for peripheral T1 lesions.33 Patients in the lobectomy group had significantly lower rates of local recurrence as well as a trend toward improved disease-free and overall survival.

Since the early 1990s, thoracoscopic or video-assisted thoracoscopic surgery (VATS) lobectomy has been shown to be an effective alternative to traditional thoracotomy for resection of early stage lung cancer. Relative to thoracotomy, advantages for thoracoscopic lobectomy include decreased acute postoperative pain, shorter chest tube duration, shorter hospital length of stay, and fewer overall postoperative (particularly pulmonary) complications.34 Moreover, patients who have undergone VATS lobectomy and require adjuvant chemotherapy are able to initiate therapy sooner and have fewer reduced doses than thoracotomy patients.35 VATS lobectomy is also cost effective.36 While there are higher operating room costs associated with VATS lobectomy, these are counterbalanced by both shorter hospital stays and overall lower morbidity.

BILOBECTOMY, PNEUMONECTOMY, AND SLEEVE RESECTIONS

Bilobectomy or pneumonectomy may be required for complete extirpation of centrally located tumors. Bilobectomy involves the en bloc resection of the right middle and lower lobes for lesions located near or within the bronchus intermedius. For pneumonectomy, division of the mainstem bronchus, main pulmonary artery and both pulmonary vein branches is undertaken.

If pneumonectomy is considered for a centrally located lesion, then a parenchymal-sparing sleeve resection should also be contemplated. The sleeve resection involves resection of the involved lobe with removal of a segment of the adjacent bronchus. A bronchial-bronchial anastomosis is then constructed to restore bronchial continuity. While technically a more complex operation, sleeve resection offers several advantages over pneumonectomy, including preserved pulmonary function, avoidance of post-pneumonectomy complications, and improved patient quality of life.37

Proper fluid management is essential for patients undergoing pneumonectomy and extrapleural pneumonectomy. The sequelae of postoperative acute lung injury and pulmonary edema can be lethal, with mortality rates up to 50%.23 Management of hypotension should include consideration of vasopressor and/or inotropes in lieu of additional intravenous fluids, once blood losses are accounted for by the anesthesiologist. In addition, adequate pain management, usually in the form of a thoracic epidural catheter, helps to avoid respiratory compromise and postoperative pneumonia.

EXTRAPLEURAL PNEUMONECTOMY (SEE ALSO CHAPTER 14)

Extrapleural pneumonectomy is most often performed for treatment of malignant mesothelioma, a relatively uncommon but highly lethal disease associated with smoking and asbestos exposure. The operation requires extrapleural dissection of the lung with en bloc resection of the lung, pericardium and diaphragm. The pericardium and diaphragm are subsequently reconstructed, usually with gore-tex. Malignant mesothelioma, its treatment options and anesthetic implications are discussed in detail in Chapter 14.

TRACHEAL AND CARINAL RESECTIONS

Communication between the surgeon and anesthesiologist is critical for the patient undergoing tracheal and carinal resection. For patients with near-obstructing lesions, an inhalational induction technique with maintenance of spontaneous breathing is preferred, as positive pressure ventilation may result in complete obstruction.38,39 Patients without critical stenoses may be maintained with intravenous anesthesia, which allows for prompt reversal and extubation following the procedure. Sterile anesthetic tubing and connectors should be available in the operating room for these procedures. In addition, resections involving the lower trachea and carina may require the use of an extra long, armored endotracheal tube, which can be placed into one of the mainstem bronchi using bronchoscopic guidance for ventilation during construction of the anastomosis. At the conclusion of the procedure, the orotracheal tube is replaced and the armored tube removed.

ESOPHAGEAL RESECTIONS (SEE ALSO CHAPTER 17)

Esophagogastrectomy is indicated for the treatment of esophageal cancer and for end-stage benign esophageal disease. Chapter 17 provides an in-depth review of the topic. In summary, the procedure includes resection of the esophagus, resection of periesophageal lymph nodes for accurate staging purposes, and restoration of enteric continuity. The esophageal reconstruction is usually performed using the stomach as an esophageal conduit; if the stomach is not available, other options include a pedicled segment of right or left colon, or jejunum (either pedicled or free). There are several accepted and described techniques for esophageal resection, including transhiatal, transthoracic (Ivor Lewis), 3-incision (McKeown), or minimally invasive esophagogastrectomy (MIE). The specific technique employed depends somewhat on tumor location as well as surgeon and patient preference. The specific incisions employed and some of the advantages and disadvantages to each technique are described in Table 8–4.

Table 8–4. Summary of Esophageal Resection Procedures

image

Anesthetic management of patients undergoing these procedures includes standard monitors, large bore or central venous access, and arterial line monitoring. For procedures involving anastomosis in the left neck, central venous access (if necessary) should be accomplished through the right internal jugular vein. The Ivor Lewis, McKeown and MIE procedures require one-lung ventilation to facilitate the dissection and mobilization of the esophagus.

The transhiatal esophagogastrectomy is accomplished through a laparotomy with anastomosis in the neck. Dissection of the intrathoracic esophagus is accomplished bluntly through the esophageal hiatus; the presence of the surgeon’s hand in the mediastinum may compromise venous return, resulting in transient hemodynamic instability. Good communication between the surgeon and anesthesiologist is especially important during this portion of the operation. Normal fascial planes may be disrupted due to the presence of the tumor. As such, the transhiatal esophagogastrectomy is not suitable for mid-esophageal tumors, where the airway (adjacent to the esophagus) is at risk for injury during the blunt dissection. If an airway injury is detected during the procedure, advancing the endotracheal tube past the injury will provide a temporary means of ventilation until the defect can be repaired.

The Ivor Lewis esophagogastrectomy is a two-part operation. First, a laparotomy is performed for gastric mobilization and lymphadenectomy. Then, the patient is turned to the left lateral decubitus position and right thoracotomy is performed. There, under one-lung ventilation, the intrathoracic esophagus is mobilized and thoracic lymphadenectomy is completed. The esophagogastric anastomosis is constructed in the chest. While all anastomoses are at risk for leak, the leak rate for intrathoracic anastomoses is lower than for those constructed in the neck.40,41 However, the morbidity and mortality associated with an intrathoracic leak is significantly higher as compared to that following cervical anastomosis.42

The McKeown esophagogastrectomy is a three-part operation that first utilizes a right thoracotomy or thoracoscopy with one-lung ventilation for dissection and mobilization of the esophagus. Once the chest is closed, the patient is returned to the supine position with the head turned toward the right. A laparotomy is performed for gastric mobilization and lymphadenectomy. Finally, the gastric conduit is passed through the chest and the esophagogastric anastomosis is constructed in the left neck. Again, central venous access through the left internal jugular vein should be avoided.

A minimally invasive Ivor Lewis esophagogastrectomy employs both laparoscopy for gastric mobilization and thoracoscopy or limited thoracotomy for intrathoracic esophageal mobilization. During laparoscopy, the peritoneal space is insufflated with carbon dioxide; active ventilatory management is necessary to control the patient’s PaCO2. One-lung ventilation is necessary to complete the intrathoracic portion of the procedure. Depending on the surgeon’s experience with this procedure, operative times may be longer than that for an open operation. However, advantages to this technique include lower blood loss, less pain and shorter length of hospital stay.43

SUMMARY

The successful management of patients undergoing thoracic surgery requires an understanding of each patient’s anatomy and physiology, the past medical and surgical history, as well as the planned operative procedure. Anticipation and management of potential intraoperative and postoperative complications will help to reduce their incidence. Clear communication between surgeon and anesthesiologist both before and during the procedure facilitates optimal patient care.

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