|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Mediastinoscopy is commonly performed before thoracotomy to establish a diagnosis or to determine the resectability of a lung carcinoma (or both). After a suprasternal notch incision, a tunnel is created (through the pretracheal fascia) by blunt dissection along the anterior and lateral walls of the trachea into the mediastinum, behind (posterior to) the aortic arch down to the subcarinal area ( Fig. 49-34 ). This procedure allows for direct inspection and biopsy of the superior mediastinal lymph nodes, which lie posterior to the aortic arch (the anterior and lateral para-main stem bronchial, anterior subcarinal, anterior and lateral paratracheal lymph nodes) (see Fig. 49-34 ). Tumors of the thymus and anterior mediastinum are not examined by the usual diagnostic mediastinoscopic approach because they are anterior to the great vessels; thus, anterior mediastinotomy is required to examine this area (this procedure uses a parasternal second-inner space incision and is a less complicated procedure than mediastinoscopy). Previous mediastinoscopy is a nearly absolute contraindication to
Figure 49-34
Schematic diagram showing placement of a mediastinoscope
into the superior mediastinum. The mediastinoscope passes anterior to the trachea
but behind the thoracic aorta. This location allows for sampling of the anterior
and lateral para-main stem bronchial lymph nodes, anterior subcarinal lymph nodes,
and anterior and lateral paratracheal lymph nodes. Anatomic structures that can
be compressed by the mediastinoscope (see areas marked by asterisks)
and result in major complications are the thoracic aorta (rupture, reflex bradycardia),
innominate artery (decreased right carotid blood flow can cause cerebrovascular symptoms,
and decreased right subclavian flow can cause loss of the right radial pulse), trachea
(inability to ventilate, stimulus to cough), and vena cava (risk of hemorrhage with
superior vena cava syndrome).
In addition to the usual preanesthetic evaluation of patients, one should specifically look for the signs and symptoms of relative contraindications to mediastinoscopy, such as obstruction or distortion of the upper airway and obstruction of the superior vena cava, signs and symptoms of impaired cerebral circulation (which may be compounded during mediastinoscopy by compression of the innominate artery), and evidence of myasthenic syndrome from lung carcinoma. Because of the potential risk of hemorrhage, a large-bore intravenous catheter should be inserted, and blood should be immediately available during the procedure. If the superior vena cava is obstructed, a lower extremity intravenous catheter is mandatory.
Although mediastinoscopy can be performed under local anesthesia, [484] [485] general anesthesia with controlled positive-pressure ventilation is preferred because it allows the surgeon more flexibility in dissection, minimizes the potential for air embolism (see later), and facilitates the management of major complications such as massive hemorrhage.[486] However, local anesthesia may be considered in patients with active cerebrovascular disease to continuously monitor cerebral function in the awake state.
After the intravenous induction of general anesthesia and paralysis with either succinylcholine, atracurium, or vecuronium, lidocaine is sprayed directly on the trachea and given intravenously to minimize coughing during orotracheal intubation and the procedure itself. Use of a nonkinking tube should be considered in cases in which tracheomalacia is a possibility. Neuromuscular blockade is also performed during the procedure to prevent coughing, venous engorgement from straining, and movement during the procedure. The head-up position minimizes venous engorgement but maximizes the potential for venous air embolism. During mediastinoscopy, the anesthesiologist's attention is primarily focused on detecting the occurrence of complications of the procedure by monitoring right upper extremity blood pressure (the vessels most commonly compressed are the innominate and the right subclavian and carotid arteries) and by observing for reflex bradycardia (compression of the aorta), arrhythmias (mechanical stimulation of the aorta), hypovolemia, tension pneumothorax, and compression of the trachea (see later). Blood pressure and oxygen saturation should be measured in the left arm; if an arterial line is placed, the right wrist may be preferable
Although overall mortality from this procedure is low (0.1%)[487] and one institution has even undertaken the performance of ambulatory (outpatient) mediastinoscopy in a hospital-based surgical suite,[488] serious complications can occur and the anesthesiologist must be prepared to diagnose and treat them. In a series of 6490 patients undergoing mediastinoscopy, the major complications reported (number of patients in parentheses) consisted of hemorrhage (48), pneumothorax (43), recurrent laryngeal nerve injury (22), infection (22), tumor implantation in the wound (8), phrenic nerve injury (3), esophageal injury (1), chylothorax (1), air embolism (1), and transient hemiparesis (1).[487] The overall complication rate in various studies has been 1.5% to 3.0%.[487] [488] [489] [490] [491] [492] [493] [494] At the time of occurrence, most of the complications listed required a specific anesthetic management response.
Significant (occasionally massive) hemorrhage has been the most frequent major problem encountered during mediastinoscopy. If it occurs, thoracotomy must be performed immediately. While preparations for median sternotomy are in progress, the surgeon should attempt to control hemorrhage by compressing the bleeding site with a sponge forceps or a small pack, although the relative inaccessibility of the operative field may make this maneuver difficult or ineffective. The anesthesiologist should (1) rapidly begin volume replacement thorough one or more large-bore intravenous cannulas that have been placed before induction of anesthesia, (2) send for blood that was reserved for the patient preoperatively, (3) support the circulation pharmacologically until volume replacement is achieved, (4) ensure adequate oxygenation and ventilation, (5) administer atropine for reflex bradycardia from aortic compression (if it occurs), and (6) discontinue or reduce the dose of all anesthetic drugs until normovolemia is reestablished. Rarely, it may be necessary to induce deliberate hypotension to control bleeding in this setting.[490] If hemorrhage originates from a tear in the superior vena cava, volume replacement and drug treatment may be lost into the surgical field unless they are administered through a peripheral intravenous line placed rapidly in the lower extremity.[490]
Pneumothorax is another relatively frequently encountered complication of mediastinoscopy. It is not usually apparent until the postoperative period, and most patients do not require chest tube decompression. All patients should be monitored for signs of pneumothorax in the postoperative period and a chest radiograph obtained when doubt exists. Pneumothorax that occurs intraoperatively, as evidenced by increased peak inspiratory pressure, tracheal shift, distant breath sounds, hypotension, and cyanosis, requires immediate treatment by chest tube decompression.[495]
When mediastinoscopy causes injury to the recurrent laryngeal nerve (see Fig. 49-34 ), it is permanent in approximately 50% of patients.[487] If injury to the recurrent laryngeal nerve is suspected, the vocal cords should be visualized while the patient is spontaneously breathing (usually at the time of extubation). If the vocal cords are not moving or are in a midline position (or both), consideration has to be given to the problem of postoperative laryngeal obstruction.
During mediastinoscopy, the tip of the mediastinoscope is located intrathoracically and therefore directly exposed to pleural pressure. Venous air embolism (when venous bleeding is present) can occur much more easily if patients are breathing spontaneously because of the development of negative intrathoracic pressure during inspiration; therefore, controlled positive-pressure ventilation during this procedure minimizes the risk of air embolism.
As noted, the mediastinoscope can exert pressure against the innominate artery and cause diminished blood flow to the right carotid and right subclavian arteries (see Fig. 49-34 ). This phenomenon may be of special significance in patients with preexisting compromised cerebral circulation. Compression of the right carotid artery has been proposed as the cause of left hemiparesis that occurred in one patient and subsequently cleared 48 hours after the procedure.[487] In another patient, compression of the right subclavian artery caused loss of the pulse and blood pressure in the right arm and was misdiagnosed as an intraoperative cardiac arrest.[496] In another study, blood pressure in the right arm was significantly decreased from 15 to 360 seconds in four of seven patients who underwent mediastinoscopy.[497] This last report therefore recommended that blood pressure be measured in the left arm and the right radial artery be continuously monitored by palpation or finger plethysmography during mediastinoscopy. A right radial arterial line would, of course, very sensitively and continuously monitor the occurrence of innominate or right subclavian artery compression. An oxygen saturation monitor would do this task less sensitively. Any decrease in right radial artery pressure requires repositioning of the mediastinoscope, especially in patients with cerebral vascular insufficiency. Preventing excessive extension of the neck, which might contribute to pinching of neck vessels, is also important in this group of patients.
Autonomic reflexes may result from compression or stretching of the trachea, vagus nerve, or great vessels. Sudden changes in pulse or blood pressure, or both, during mediastinoscopy may initially be empirically treated by repositioning the mediastinoscope. Atropine is given for persistent bradycardia.
The anesthetic considerations for anterior mediastinotomy are similar to those for mediastinoscopy except that the incision is larger, the incidence of complications is lower because structures can be visualized and controlled more readily, the position of the head is unimportant, and blood pressure can be measured in either arm because there is little chance of compression of the innominate artery.
Diagnostic thoracoscopy (pleuroscopy) permits examination of the intrathoracic cavity and is most commonly performed to aid in the diagnosis of pleural and parenchymal disease, to help establish the staging of suspected neoplasms, and to determine the etiology of recurrent pleural effusions.[498] [499] [500] [501] [502] It is most often performed after thoracocentesis or closed-chest pleural or lung biopsy has been performed and a diagnosis has still not been established.
The development of endoscopic video systems and instrumentation (stapling devices, dissectors, coagulators, autotyping sutures, and the neodymium:yttrium-aluminum-garnet [Nd:YAG] laser) has permitted therapeutic thoracoscopy for a wide variety of major thoracic procedures. These procedures include biopsy of many intrathoracic structures, peripheral wedge and sublobar resection, lobectomy, removal of mediastinal cysts, closure of persistent or recurrent pneumothoraces and leaking blebs, pleurodesis, dorsal thoracic sympathectomy, drainage of spinal abscesses, resection of posterior mediastinal neurogenic tumor, retrieval of intrathoracic (pleural) foreign bodies, definitive treatment of postpneumonectomy chylothorax, and facilitation of pericardectomy. [503] [504] [505] [506] [507] [508] Thoracoscopy is performed by making a small incision in the lateral thoracic wall (usually at the level of the sixth intercostal space) and then introducing a thoracoscope, laparoscope, or mediastinoscope into the pleural cavity. The procedure allows for complete inspection of the pleural space of a hemithorax. Fluid and biopsy specimens can usually be obtained easily through the incision, although many surgeons prefer to use a separate incision for additional instruments such as biopsy forceps.
Thoracoscopy can be performed under either local, regional, or general anesthesia with one-lung ventilation. Local anesthetic infiltration of the lateral thoracic wall and parietal pleura is the simplest way to provide anesthesia, [509] although some patients may experience considerable discomfort when this method is used. Partial collapse of the lung on the operated side occurs when air enters the pleural cavity. This technique allows for good visualization of the pleural space by the surgeon. It is both hazardous and unnecessary to insufflate gases under pressure into the hemithorax under examination to increase visualization of the pleural space. Surprisingly, even though many of these patients suffer from advanced pulmonary disease, changes in PaO2 , PaCO2 , and cardiac rhythm are usually minimal during the procedure when it is performed under local anesthesia and the patient is breathing spontaneously.[510] [511] However, it is prudent to use a high FIO2 to overcome the loss in lung volume caused by the unavoidable pneumothorax.
Intercostal nerve blocks performed at the level of the incision and for two interspaces above and below may provide more complete analgesia for thoracoscopy, especially if they are placed far enough posteriorly to anesthetize the parietal pleura. The addition of an ipsilateral stellate ganglion block helps prevent the cough reflex that is sometimes elicited during visualization and manipulation of the hilum.
When thoracoscopy is performed under general anesthesia, a DLT should be used. Positive-pressure ventilation seriously interferes with visualization of the thoracic contents, and thoracoscopy is therefore a relatively strong indication for one-lung ventilation. If the procedure is short and the ipsilateral lung needs to be deflated for only a brief period, blood gases are not routinely monitored during the procedure. However, for patients with marginal pulmonary status in whom the period of one-lung ventilation lasts for more than a few minutes, the usual monitoring precautions should be taken.
Complications are rare during this simple procedure, although it is possible that any structure that the surgeon has to manipulate may be damaged. A few critically ill spontaneously breathing patients may experience impaired gas exchange during the procedure. Some air may transiently remain in the pleural space after the procedure, and this situation may require insertion of a chest tube.
|
|
|
|
|
|
|
|
|
|
|
|
|
