Thoracic Anesthesia

PART 2

Thoracic Anesthesia Practice


CHAPTERS


 

10
Bronchoscopy, Mediastinoscopy, and Chamberlain Procedure

Frederick W. Lombard
Jorn Karhausen


Key Points

• Diagnostic bronchoscopy is now usually performed using flexible equipment, whereas therapeutic bronchoscopy may be conducted with both flexible and rigid equipment. A thorough appreciation of both is essential for safe anesthetic management in the bronchoscopy suite.

• Unexpected massive bleeding is always possible during cervical mediastinoscopy, and thus anesthesiologists should be prepared to administer large volume resuscitation at a moment’s notice.

• Right radial artery cannulation is preferred in order to alert the surgeon to innominate artery compression with risk of cerebral ischemia.



Case Vignette


A 75-year-old male presented with a three-month history of cough. He has been treated with two courses of antibiotic therapy after which a chest radiograph revealed a suspicious left upper lobe lesion. He is now referred for staging bronchoscopy and mediastinoscopy following a computed tomography (CT) scan, which confirmed the 3.5 × 3 cm mass, and also showed enlarged subaortic lymph nodes. He has hypertension and chronic obstructive pulmonary disease due to a 40-pack year smoking history. Medications include furosemide and aspirin.

Vital signs: BP 175/85, HR 72, room air SpO2 95%. Laboratory examination is normal except for a BUN of 25, creatinine of 1.8 and potassium of 3.2. His CXR is notable for the left upper lobe mass and mild centrilobular emphysema.


With the growing use of computed tomographic (CT) scanning, pulmonary lesions are being diagnosed with increasing frequency. In fact, incidental lesions found on chest x-ray (CXR) or CT have become the most common manifestation of lung cancer.1 A lesion larger than 3 cm in diameter is considered a mass, and as such has a greater likelihood of being malignant.1 A single pulmonary lesion that is less than 3 cm in diameter, completely surrounded by pulmonary parenchyma, and is not associated with atelectasis or adenopathy is defined as a solitary pulmonary nodule (SPN).1 While as many as one-third of SPNs represent primary malignancies, and nearly one quarter may be solitary metastases, the differential diagnosis of an SPN is broad and includes vascular diseases, infections, inflammatory conditions, congenital abnormalities and benign tumors.1

In managing patients with suspected lung cancer, the goals are to determine an accurate histological diagnosis and stage the disease, if the lesion is malignant. This information is critical, not only to predict resectability, but also to avoid unnecessary surgery and provide the patient with prognostic information. Flexible fiberoptic bronchoscopy (FOB) and mediastinoscopy are the standard methods used for staging non-small cell lung cancer (NSCLC), the most prevalent type of lung cancer.

FLEXIBLE FIBEROPTIC BRONCHOSCOPY

Flexible fiberoptic bronchoscopy (FOB) is utilized extensively in the initial evaluation of patients suspected of having lung carcinoma. FOB enables direct visualization of the bronchial mucosa down to the level of the segmental and proximal subsegmental bronchi. At these levels direct visually guided biopsy is possible. FOB also enables endobronchial brushing and bronchoalveolar lavage (BAL) of disease beyond direct visualization.

Since its introduction into clinical practice in the early 1970s, FOB technology has undergone continuous improvement and innovation. Transbronchial needle aspiration (TBNA) was added in the early 1980s, a technique that has now been refined by the addition of image guidance, such as endobronchial ultrasound (EBUS), to enhance diagnostic precision. EBUS can be used for diagnostic aspiration of both mediastinal lymph nodes and central parenchymal lung lesions, not visible during routine bronchoscopy.2 The more recent addition of fluorescence-reflectance bronchoscopy may also increase sensitivity in detecting early endobronchial lesions, such as moderate or severe dysplasia, carcinoma in situ and microinvasive cancer.2

The role of FOB in the evaluation of patients with lung cancer is twofold: (1) to confirm the diagnosis of cancer and determine the histology, and (2) to rule out the presence of endobronchial tumor in the proximal airways, ie, tumor staging.

In patients with clinical or radiographic evidence of endobronchial disease, such as hemoptysis or lobar atelectasis, FOB has a high yield, and FOB may provide a histologic diagnosis of lung cancer in up to 90% of cases. However, in patients with SPN the yield is much lower, and the level of evidence supporting bronchoscopy in this population is therefore lower. Nevertheless, almost 10% of patients with SPN may have evidence of an endobronchial lesion, and these lesions are best diagnosed using bronchoscopy.3

Indications for Flexible Fiberoptic Bronchoscopy

The utility of FOB extends well beyond its role in lung cancer. The diagnostic and therapeutic indications for FOB are summarized in Table 10–1.

Table 10–1. Indications for Flexible Fiberoptic Bronchoscopy

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Procedural Complications

Flexible bronchoscopy, even when combined with biopsy, TBNA or BAL, is a very safe procedure. Reported mortality rates are 0.02% to 0.04%4,5 and major complications occur in 0.12% to 0.5% of patients during simple bronchoscopies. However, when combined with TBNA complications have been reported in up to 6.8%.4,5

HYPOXEMIA

Hypoxemia is common during flexible bronchoscopy, especially when additional procedures such as BAL are performed, during which substantial decreases in arterial oxygen tension (PaO2) may occur. Hypoventilation, the most frequent cause of hypoxemia during bronchoscopy, may result from respiratory depression due to sedation, increased airway resistance or airway circuit leaks. Oxygen supplementation is therefore required during the procedure and often following the procedure, depending on the patient’s pulmonary function and degree of residual sedation.

CARDIAC ARRHYTHMIAS

Both brady- and tachy-arrhythmias have been reported during fiberoptic bronchoscopy. Arrhythmias most commonly occur as a result of autonomic stimulation due to passing the endoscope through the vocal cords, or during procedures such as TBNA or BAL. Physiological derangements such as hypoxia or hypercarbia should be ruled out as potential contributing factors.

BRONCHOSPASM

Bronchospasm seldom complicates FOB in the general population, but may be more common in patients with reactive airways disease.6 Nevertheless, even in patients with more severe reactive airways disease (forced expiratory volume in 1 second image bronchoscopy, BAL and biopsy are generally well tolerated. Premedication with a bronchodilator may prevent decreases in postoperative FEV1 and is recommended in patients with reactive airways disease.7

BLEEDING

While FOB is rarely complicated by significant hemorrhage, TBNA may result in substantial bleeding in 1.6% to 4.4% of cases.8,9 Patient risk factors for bleeding include immunosuppression, uremia, pulmonary hypertension, liver disease, coagulation disorders, and thrombocytopenia. Patients with superior vena cava syndrome have a further increased risk for bleeding due to venous engorgement.

PNEUMOTHORAX

Although uncommon, pneumothorax requiring pleural drainage may complicate approximately 3.5% of cases where TBNA is performed.10 Positive pressure ventilation increases the risk for pneumothorax during TBNA.11 While the signs and symptoms of pneumothorax may be delayed after TBNA, it is very uncommon for a pneumothorax to develop more than 1 hour after the procedure.12,13 It is therefore recommended to obtain a CXR at least 1 hour after TBNA to exclude this complication.

FEVER

Fever is common following FOB and may occur in up to 18.2% of patients. When combined with BAL the incidence further increases from 37% to 52.5%.14,15 Bacteremia rates however are lower, occurring in 6.5% of patients following bronchoscopy with BAL.16 This rate compares favorably to rates of 2.3% to 11.8% following direct laryngoscopy and intubation,17,18 and no association with infectious sequelae has been established. Pro-inflammatory cytokines from alveolar macrophages are thought to play a role in the observed febrile reaction.19 Therefore, unless the procedure involves incision of the respiratory tract mucosa, or drainage of an abscess or empyema, published guidelines do not recommend antibiotic prophylaxis against endocarditis.20

Anesthetic Management for Fiberoptic Bronchoscopy Procedures

PREOPERATIVE ASSESSMENT

Most patients with lung cancer have a history of smoking and therefore have some degree of chronic obstructive pulmonary disease. The preoperative assessment should identify reversible reactive airway disease, which warrants preoperative bronchodilator therapy.6,7 A history of chemo or radiation therapy should alert the anesthesiologist to the possible risk of pulmonary oxygen toxicity, in which case the lowest possible inspired oxygen partial pressures (FiO2) should be used.

MONITORING

FOB can be performed in awake patients under local anesthesia or under general anesthesia. Regardless of the anesthetic approach, standard monitoring should include ECG, pulse oximetry, and noninvasive blood pressure monitoring.

AWAKE BRONCHOSCOPY

When performed in the awake patient, adequate local anesthesia is the most important component of the anesthetic. Relying on heavy sedation to suppress laryngeal and airway reflexes could result in hypoventilation and hypoxemia, especially in patients with limited respiratory reserve. Multiple topical nasal and oral applications of any commercially available local anesthetic preparation for this use usually suffice. Blocking individual nerves or transtracheal injections of a local anesthetic solution are rarely required. A topical vasoconstrictor (such as oxymetazoline) and a systemic antisialagogue (such as glycopyrrolate) are usually administered as well. Supplemental oxygen therapy should be administered routinely.

BRONCHOSCOPY UNDER GENERAL ANESTHESIA

When FOB is scheduled in addition to surgical procedures that require general anesthesia, general endotracheal anesthesia with positive pressure ventilation is the preferred technique. Either an inhalational or intravenous anesthetic approach, combined with a short-acting muscle relaxant, would be acceptable. The endotracheal tube should be secured with the tip of the tube well above the carina to allow an unobstructed view of the carina. It is important to use an endotracheal tube with an internal diameter of at least 8.0 mm to diminish the detrimental effects of the functional reduction in internal diameter. A 5.7 mm bronchoscope will occupy only 10% to 15% of the cross-sectional area of the trachea, but 40% of a 9.0 mm tube and 66% of a 7.0 mm endotracheal tube.7 The endotracheal tube could be trimmed in length to further reduce resistance, but this is seldom required. Additionally, PEEP should be avoided and ventilator settings should allow sufficient time for expiration. Failing to do so may result in distal air trapping.

Spontaneous ventilation should be avoided due to the increase in effective airway resistance and work of breathing. An endotracheal tube connector with a perforated diaphragm, designed to minimize circuit leaks, allows the use of positive pressure ventilation during bronchoscopy. Nevertheless, circuit leaks often render tidal volume monitoring unreliable, and ventilation should be monitored by paying attention to chest wall movement and capnography. Ventilation could be adjusted by adjusting the inspiratory pressure and respiratory rate. However, because the FOB procedure is of short duration, hypercapnia could be tolerated, and attention should rather be focused on maintaining arterial oxygen saturation and avoiding lung injury due to air trapping. Should arterial desaturation occur despite a high FiO2, the bronchoscope should be removed and the lungs manually ventilated until oxygenation has been restored. Even though pneumothorax is rare, this complication should be ruled out if arterial desaturation does not resolve readily, or is associated with hypotension.

Some centers employ laryngeal mask airways for FOB, with either controlled ventilation (if the peak airway pressure can be maintained <25 cm H2O) or spontaneous ventilation. Injection of local anesthetic down the suction channel of the bronchoscope facilitates passage of the instrument, and this approach permits examination of the glottis and immediate subglottic trachea. It also reduces the number of direct laryngos-copies if the case immediately precedes a lung resection.

RIGID BRONCHOSCOPY

While routine rigid bronchoscopy has been supplanted by FOB for most cases, it is still widely used and has even experienced a resurgence with the introduction of laser airway surgery and the advent of airway stents over the past 2 decades.21 The rigid bronchoscope is a straight hollow metal tube through which direct access to the central airways can be obtained (Figure 10–1). It has a blunted distal opening, which is beveled to facilitate lifting of the epiglottis and atraumatic intubation of the airway. The distal end of the bronchoscope has side vents, which enables ventilation of the opposite lung when the distal opening is advanced into a main stem bronchus. These side vents may result in an air-leak into the pharynx during positive pressure ventilation when not advanced beyond the vocal cords. The proximal opening is adapted to accommodate attachments, provide side port ventilation, and permit insertion of surgical instruments.

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Figure 10–1. A and B. Standard rigid bronchoscopy equipment.

Indications for Rigid Bronchoscopy

The advantages of rigid bronchoscopy over FOB are that it permits continuous assisted ventilation while simultaneously permitting access for a variety of surgical and diagnostic instruments (including FOB to inspect airways distal to the central airways). The specific indications are listed in Table 10–2.

Table 10–2. Indications for Rigid Bronchoscopy

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Procedural Complications

Rigid bronchoscopy could lead to the same potential complications seen following FOB, but is associated with more trauma than with FOB.22 Insertion of the rigid bronchoscope can result in dental damage or laceration of the mucosa of the oropharynx, larynx, or bronchial tree. In patients with cervical spine disease, hyperextension could lead to spinal injuries or even cerebral ischemia due to vertebral artery occlusion.

Anesthetic Management for Rigid Bronchoscopy Procedurres

MONITORING

Invasive arterial pressure monitoring should be considered in addition to routine monitoring. Rigid bronchoscopy is an extremely stimulating procedure, and invasive arterial pressure monitoring enables swift detection of hemodynamic changes and the response to pharmacological intervention. It also enables monitoring of arterial carbon dioxide partial pressure (PaCO2) during jet or apneic ventilation. Continuous quantitative neuromuscular monitoring should be performed to ensure adequate relaxation during the procedure and the return of normal neuromuscular function prior to emergence by assessing train-of-four (TOF) ratio. The use of bispectral index (BIS) or entropy monitoring is strongly recommended, because rigid bronchoscopy is a high-risk procedure for intraoperative awareness.

INDUCTION AND MAINTENANCE

Rigid bronchoscopy is now always performed under general anesthesia. Neuromuscular blockade facilitates atraumatic intubation and prevents sudden movement or coughing, which could result in serious airway injury. The anesthetic plan should allow for rapid emergence and extubation following completion of the surgical procedure. A routine intravenous induction can be used and mask ventilation with 100% oxygen should be established until the patient is fully paralyzed, at which time the airway is handed over to the surgeon. The choice of drugs depends on patient factors and the expected duration of the procedure. When jet ventilation is used during bronchoscopy, a total intravenous anesthetic approach, such as a propofol infusion, is required. Since surgical stimulation can be profound but postoperative pain generally minimal, remifentanil is commonly used during rigid bronchoscopy. The choice of muscle relaxant depends on the expected duration of the procedure.

VENTILATION

Ventilation can be managed by connecting the standard anesthesia circuit to the bronchoscope (ventilating bronchoscope) or by using a jet ventilator. When using a ventilating bronchoscope, positive pressure ventilation can only be applied as long as the eyepiece is closed over the bronchoscope. Ventilation must therefore be interrupted when suction catheters and surgical instruments are passed through the scope. In the absence of ventilation, adequate oxygenation can be maintained for several minutes (apneic oxygenation), especially when preceded by a period of hyperventilation with 100% oxygen to achieve hypocapnia and denitrogenation. Provided hypercapnia and respiratory acidosis can be tolerated, oxygen insufflation through a small catheter in the trachea can maintain oxygenation. Arterial PCO2can be expected to rise by 6 to 10 mm Hg during the first minute of apnea, and at a rate of 3 to 5 mm Hg/min thereafter. Ventilation should therefore be resumed after about 8 to 10 minutes, unless required earlier due to hypoxemia.

For prolonged rigid bronchoscopy jet ventilation is recommended (see Figure 10–1). The intermittent high-velocity oxygen jet entrains air into the bronchoscope, resulting in expansion of the lungs. Jet systems can be divided into manually triggered systems (Sanders’ type) or those with automatic timing. Jet ventilation is initiated at a low frequency, using a lower driving pressure (20 psi), which is then gradually increased until adequate chest rise and breath sounds are observed. High-frequency jet ventilation (HFJV), using ventilatory rates of 150 to 300 breaths/min, will result in lower mean airway pressure and less movement in the bronchial tree, which might be desirable during laser treatment. However, low frequency jet ventilation might result in less air trapping in patients with bronchial stenoses, or improved ventilation in the opposite lung through the bronchoscope side vents during endobronchial intubation.23

EMERGENCE

Once the bronchoscope is removed, the patient should be intubated with an endotracheal tube prior to reversal of neuromuscular blockade and emergence. A laryngeal mask airway or face mask with or without an oral airway may also be considered, provided airway resistance and pulmonary compliance permits adequate ventilation with airway pressures less than 15 to 20 cm H2O.24 Full return of neuromuscular function (TOF ratio > 90%) should be confirmed prior to emergence, to enable a strong cough for clearing secretions or blood.

MEDIASTINOSCOPY

Indications

Mediastinoscopy is an invasive diagnostic procedure used to biopsy lymph nodes and masses in the mediastinum. In NSCLC, the most common indication for mediastinoscopy, the level of nodal involvement has significant prognostic importance. In general, positive mediastinal findings on CT or PET need to be confirmed histologically. Compared to less invasive diagnostic modalities, such as transbronchial fine needle aspiration and tracheal endoscopic ultrasound needle aspiration, mediastinoscopy remains the gold standard due to its superior sensitivity (>80%) and specificity (100%).25Mediastinoscopy also plays an important role in the diagnostic workup of other diseases presenting with mediastinal lymphadenopathy, such as sarcoidosis or lymphoma. Cervical mediastinoscopy, the most conventional form of mediastinoscopy, is used to evaluate the superior and middle mediastinal compartments. Other approaches have been devised to gain access to lymph nodes and masses that are not accessible through the cervical approach and will be described later.

Absolute contraindications to cervical mediastinoscopy are rare. Where technically not feasible, due to extreme kyphosis or previous radical laryngectomy, this procedure should not be attempted. Conditions such as superior vena cava syndrome, enlarged goiter, or previous mediastinoscopy, sternotomy, or radiation therapy do not necessarily preclude cervical mediastinoscopy. However, due to adhesions and fibrosis the procedure may be challenging under these conditions.

Anatomy

The mediastinum is anatomically one of the most complex regions of the human body. It lies between the two pleural cavities, is bounded by the sternum anteriorly and the vertebral column posteriorly, and extends from the thoracic inlet down to the diaphragm. For purposes of description, the mediastinum is divided into two parts by the transverse thoracic plane (Figure 10–2). This slightly oblique plane extends posteriorly from the sternomanubrial angle to the junction of the 4th and 5th thoracic vertebra. The inferior mediastinum is further divided into the posterior (behind the pericardium), middle (containing the pericardium and its contents) and anterior (in front of the pericardium) compartments. Apart from the lungs, all the thoracic viscera are contained within the mediastinum, surrounded by loose connective tissue.

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Figure 10–2. Anatomical compartments of the mediastinum.

The mediastinum is rich in lymph nodes, which run in parallel with the major vessels that transgress this space. Inflammatory disease, primary lymphatic tumors and metastatic disease may affect mediastinal lymph nodes. The prognostic importance of the level and extent of nodal involvement in NSCLC has led to the development of the Mountain–Dressler lymph node map (Figure 10–3).

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Figure 10–3A. The Mountain–Dressler lymph node map showing nodal sections used in the staging of non-small cell lung cancer. Station 1 nodes are located above the sternal notch and not routinely accessible through cervical mediastinoscopy. Station 3 nodes are not seen in this view (see Figure 10-3B). (From De Leyn P, Lerut T. Conventional mediastinoscopy. Multimedia Man Cardiothorac Surg 2005. doi:10.1510/mmcts.2004.000158. Schematic 2. Copyright © 2005 European Association for Cardio-thoracic Surgery, with permission.)

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Figure 10–3B. Station 3 nodes are also not accessible by conventional cervical mediastinoscopy. Station 3A lymph nodes are anterior to the vena cava; 3P lymph nodes are reside above the tracheal bifurcation, in the upper paraesophageal region. (From De Leyn P, Lerut T. Conventional mediastinoscopy. Multimedia Man Cardiothorac Surg 2005. doi:10.1510/mmcts.2004.000158. Schematic 5. Copyright © 2005 European Association for Cardio-thoracic Surgery, with permission.)

Surgical Approaches and Considerations

A range of techniques have been developed to provide surgical access to the different regions of the mediastinum for staging mediastinoscopy. Standard cervical mediastinoscopy remains the gold standard for staging the superior mediastinal lymph nodes, but it cannot reach the subaortic (station 5) and para-aortic (station 6) nodal stations. Bronchogenic carcinoma of the left lung may metastasize to these lymph nodes, especially those tumors located in the upper lobe and hilum. Therefore, surgical staging of bronchogenic carcinoma of the left lung may require the combination of standard cervical mediastinoscopy with other surgical techniques, such as left parasternal mediastinotomy (Chamberlain’s procedure), left thoracoscopy, or extended cervical mediastinoscopy to explore the subaortic and para-aortic nodal stations.

Modifications to the conventional mediastinoscope have been introduced since the 1990s. Newer devices include integrated optics that connect to a video system, and have greatly aided in the standardization and training of this procedure. A self-supported, two-bladed spreadable video-mediastinoscope developed by Linder and Dahan in 1992 allows increased exposure of mediastinal structures and bimanual dissection. This device has facilitated the development of new minimally invasive surgical techniques for the mediastinum. The best documented method is video-assisted mediastinoscopic lymphadenectomy (VAMLA), which may improve accuracy for lung cancer staging and allow definitive mediastinal surgery in selected cases.26-28

Cervical Mediastinoscopy

The great majority of mediastinoscopies are performed through a small cervical incision just above the suprasternal notch, as first reported by Carlens in 1959. This technique allows evaluation and sampling of upper paratracheal (station 2L and 2R), lower paratracheal (station 4L and 4R), and subcarinal (station 7) lymph nodes. The 2003 American College of Chest Physicians guidelines on lung cancer staging recommend that these five nodal stations be routinely examined and that at least one node be sampled from each location unless none is present.29 The surgical procedure involves sharp dissection to expose the pretracheal muscles, which are then separated in the midline to reach the pretracheal fascia. Following incision of the pretracheal fascia, blunt dissection is then performed along the anterior surface of the trachea to develop the tissue plane down to the level of the carina (Figure 10–4). The rigid mediastinoscope is then passed along this tissue plane, posterior to the innominate artery and aorta. Through the mediastinoscope, lymph nodes are first mobilized using a blunt suction device, and then biopsied using a biopsy forceps.

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Figure 10–4. Cervical mediastinoscopy. Note the position of the mediastinoscope in relation to the anatomic structures of the mediastinum. The innominate artery is being partially occluded (“pinched”) by the instrument in this example. (From: Longnecker DE, Brown DL, Newman MF, Zapol WM. Longnecker’s Anesthesiology. Chapter 53, Thoracic Anesthesia, Figure 53-30. McGraw-Hill, Inc.: 2008, with permission.)

Anterior Mediastinotomy (Chamberlain Procedure)

Anterior parasternal mediastinotomy was introduced by McNeill and Chamberlain in 1966 to access the subaortic and para-aortic stations. The traditional anterior approach is through a mediastinotomy, requiring a parasternal incision and resection of costal cartilage. However, adequate node sampling can usually be obtained through a smaller mediastinoscopy incision in the second intercostal space, through which the mediastinoscope is inserted following blunt digital dissection. The side of the incision depends on the side of the pathology. Anterior mediastinotomy and bidigital palpation of the aortopulmonary region may be performed in conjunction with cervical mediastinoscopy to locate diseased lymph nodes (see Figure 10–3). In the event of negative biopsy results, or when the nodes or the mass cannot be safely reached, the incision can be extended and the target tissue may be biopsied from inside the pleural space by creating an anterior thoracotomy. However, anterior thoracotomy, and to some extent anterior mediastinotomy, have largely been supplanted by video-assisted thoracoscopic (VATS) exploration of the mediastinum. The advantage of anterior mediastinotomy over VATS is that the pleural space is seldom entered, obviating the need for a pleural drain, and allowing patients to be discharged on the day of surgery.

Extended Cervical Mediastinoscopy

Extended cervical mediastinoscopy provides yet another approach for staging of subaortic and para-aortic stations. This procedure is more technically challenging, but does not require an additional skin incision following the completion of standard cervical medimediastinoscopy. It is best reserved for patients with enlarged subaortic or para-aortic nodes on CT scan. Similar to anterior mediastinotomy, it is only performed when standard cervical mediastinoscopy fails to reveal involvement of superior mediastinal lymph nodes that would make the patient inoperable. The procedure should not be performed in patients with a dilated aortic arch, excessive calcification in the aortic arch or previous median sternotomy.

For extended cervical mediastinoscopy a passage is first created using digital dissection. The mediastinoscope is then advanced over the aortic arch between the innominate artery and the left carotid artery, under the left innominate vein. (see Figure 10–4). Complications related to this technique are infrequent and some authors suggest that extended cervical mediastinoscopy has less postoperative morbidity than anterior mediastinotomy or VATS. In contrast to VATS, patients can be discharged on the day of surgery.

Video-Assisted Thoracoscopy (VATS)

Thoracoscopic exploration of the mediastinum has developed into an additional minimally invasive diagnostic staging modality. In addition to allowing access to the subaortic or para-aortic lymph node stations, it also permits access to the para-esophageal (level 8) and pulmonary ligament (level 9) stations, while also providing complete visualization of the pleural space. VATS may also provide an alternative approach when there are concerns with the alternatives, such as the presence of anatomic abnormalities, previous extensive neck surgery, sternotomy or radiotherapy.

Surgical Complications

Mediastinoscopy is well-tolerated by almost all patients with a reported complication rate of 0.6% to 3% and a mortality rate of 0% to 0.05%.25,30-34 At least part of the reason for this is likely related to the fact that mediastinoscopy does not impair respiratory capacity. Only 0.1% to 0.5% of the reported complications are considered major, but the potential for catastrophic events is clear, given the close proximity to important anatomical structures. One of the most important considerations in avoiding complications is surgical experience. Video mediastinoscopy has enhanced surgeons’ ability to teach this procedure safely. The potential complications are listed in Table 10–3.

Table 10–3. Potential Complications Following Mediastinoscopy

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BLEEDING

The most feared complication, major bleeding, occurs at a rate of 0.1% to 0.4%. The vessels at risk for injury are the innominate artery, aorta, azygos vein, superior vena cava, and the pulmonary artery. Minor bleeding is common, and can safely be managed by electrocoagulation and packing. Temporary packing, endoscopic clipping, or repair via thoracotomy or sternotomy may be required occasionally. Most cases of major bleeding will require sternotomy, although right thoracotomy may be indicated when bleeding is from the first branch of the right pulmonary artery or from the azygos vein.

PNEUMOTHORAX

Pneumothorax is also rare, but reportedly 0.08% to 0.23% of patients may require chest tube placement at the end of the procedure due to a pleural tear and trauma to the lung tissue. A small pneumothorax, detected on routine postoperative chest x-ray, can be managed conservatively in asymptomatic patients.

Tracheal laceration can lead to mediastinal emphysema and decreased ventilation. In the presence of mediastinal emphysema, FOB should be performed to rule out tracheal laceration, which may warrant operative repair.

STROKE

Compression of the innominate artery during mediastinoscopy is common, and may result in transient cerebral hypoperfusion and ischemia, in particular in patients with cerebrovascular disease and inadequate collateral blood flow. Innominate artery compression can be detected in the right arm by pulse oximetry or digital palpation of an arterial pulse, but is most reliably detected by invasive arterial pressure monitoring. Hyperextension of the cervical spine could also result in vertebral artery compression, and care should be taken to avoid or limit hyperextension in patients with a history of vertebrobasilar insufficiency. The risk of stroke appears to be highest with extended cervical mediastinoscopy, and as such appears to be related to manipulation of the innominate artery and the aorta.35Stroke or transient postoperative hemiparesis are most likely caused by either atherosclerotic embolization or cerebral hypoperfusion due to prolonged compression of the innominate artery.

Bradycardia, hypotension or even asystole may result from stretching of the vagus, trachea, or great vessels, and should be managed by repositioning the mediastinoscope. Persistent bradycardia may require the administration of anticholinergic drugs such as atropine.

Anesthetic Management for Mediastinoscopy Procedures

PREOPERATIVE ASSESSMENT

The preoperative assessment should identify the presence of ischemic heart disease, cardiac arrhythmias, and cerebrovascular disease. Factors that might make the surgical procedure challenging, such as limited neck extension or superior vena cava obstruction, should also be identified. When mediastinoscopy is performed in a patient with a mediastinal mass, the preoperative assessment should also include identifying associated airway, vascular or cardiac compression.

MONITORING

Apart from standard anesthetic monitoring, right radial arterial pressure monitoring will enable accurate and immediate detection of innominate artery compression. The pulse oximeter should be placed on the right side when not using invasive arterial pressure monitoring. In both instances noninvasive blood pressure monitoring should be performed on the left. Quantitative neuromuscular monitoring should be used to ensure adequate depth of neuromuscular blockade during the procedure and complete reversal prior to emergence from anesthesia.

INTRAOPERATIVE MANAGEMENT

General anesthesia with intermittent positive pressure ventilation is the anesthetic of choice for staging mediastinoscopy. The anesthetic plan should permit rapid emergence and extubation at the end of the procedure. Because mediastinoscopy is usually combined with staging bronchoscopy, an endotracheal tube with an internal diameter of 8.0 mm or greater should be used. The endotracheal tube should be directed away from the surgical field and secured on the side toward the anesthetic machine. Connections should be secure to avoid inadvertent disconnection. Neuromuscular blockade should be maintained to prevent any sudden movement or coughing during the procedure, which may result in injury or increase the risk for bleeding due to venous engorgement. Because of the risk of intraoperative bleeding, large-bore intravenous access should be secured preoperatively and blood should be immediately available.

The patient should be positioned with the head maximally extended, with a shoulder role in place to facilitate insertion of the mediastinoscope. The anterior chest should be prepped into the field to enable immediate access for emergency median sternotomy in case of massive bleeding.

During the procedure, the primary role of the anesthesiologist should be to closely observe the patient for signs of potential surgical complications. Mediastinoscopy causes significant surgical stimulation, but this is generally of short duration and results in minimal postoperative discomfort.

POSTOPERATIVE CARE

Patients should be closely observed for airway or respiratory compromise in the immediate postoperative period. They should be recovered with the head in an elevated position to improve venous drainage and reduce the risk for airway edema. Pneumothorax should be excluded in all patients by chest x-ray. In patients with suspected recurrent laryngeal nerve injury, the vocal cords should be assessed by fiberoptic laryngoscopy.

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