1. ANESTHESIA FOR THORACIC SURGERY
Dr Abdollahi
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2. The major challenges in anesthesia for thoracic surgery
are establishing:
Adequate separation of the lungs,
Maintaining gas exchange,
Ensuring circulatory stability during one-lung anesthesia.
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3. One-lung anesthesia involves lung separation and deliberate ventilation of the dependent lung by isolating its bronchus from that of the nondependent lung (the operative site) with specially designed endotracheal tubes.
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4. In addition, thoracic surgery often involves thoracotomy incisions, which are associated with severe pain and potentially deleterious changes in cardiopulmonary physiology after surgery. Some of these physiologic changes can be minimized by thoracic epidural analgesia for effective postoperative pain management .
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5. Preoperative evaluation and preparation
Patients undergoing thoracic surgery are at high risk for
postoperative pulmonary complications, particularly if
coexisting chronic pulmonary disease is present. Risk
factors associated with increased pcrioperative morbidity
and mortality include:
The extent of lung resection (pneumonectomy>
lobectomy> wedge resection),
Age older than 70 years,
Inexperience of the operating surgeon
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6. In patients with anatomically resectable lung cancer, pulmonary function testing, lung perfusion scanning, and exercise testing to measure maximum oxygen consumption may also predict postoperative pulmonary function, as well as increased mortality .
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7. A decrease in FEV1, to less than 70% of predicted and a reduction in diffusing capacity to less than 60% of predicted should prompt further testing with a quantitative lung perfusion scan.
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8. If postoperative FEV1, or DLCO are less than 40% as predicted by lung scan, an exercise study should be obtained. A significant decrease in oxygen consumption « 10 mL/kg/min) as measured by exercise testing predicts a postoperative mortality of 25% to 50% and should prompt discussion of alternatives to surgical resection.
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9. DISCONTINUATION OF SMOKING
Smoking increases airway irritability and secretions, decreases mucociliary transport, and increases the incidence of postoperative pulmonary complications. Cessation of smoking for 12 to 24 hours before surgery decreases the level of carboxyhemoglobin, shifts the oxyhemoglobin dissociation curve to the right, and increases the oxygen available to tissues.
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10. In contrast to these short-term effects improvement in mucociliary transport and small airway function and decreases in sputum production require prolonged abstinence (8 to 12 weeks) from smoking. The incidence of postoperative pulmonary complications decreases with abstinence from cigarette smoking for more than 8 weeks in patients undergoing coronary artery bypass surgery and more than 4 weeks in patients undergoing pulmonary surgery.
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12. Nevertheless, it is useful to encourage smoking abstinence in the perioperative period, especially because smoking shortly before surgery may be associated with an increased incidence of ST-segment depression on the electrocardiogram.
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13. Management of Anesthesia
The five goals of anesthesia in thoracic surgery are to (1) produce controlled levels of narcosis and analgesia, (2) suppress cough and reflex airway activity, (3) Minimize interference with protective reflexes such as hypoxic pulmonary vasoconstriction, (4) maintain satisfactory blood gas exchange and cardiovascular stability, (5) permit rapid recovery from anesthesia to avoid postoperative respiratory depression.
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14. A practical approach is to induce general anesthesia with intravenous propofol and maintain it with a potent volatile anesthetic supplemented with intravenous opioids and controlled ventilation of the patient's lungs. Depression of airway reflexes and rapid elimination allowing for rapid recovery are important benefits of volatile anesthetics
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15. In addition, volatile anesthetics do not seem to inhibit regional hypoxic pulmonary vasoconstriction and thus aid in the maintenance of arterial oxygenation during one-lung anesthesia
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16. If nitrous oxide is administered, the inhaled concentration is often limited to 50% until the adequacy of oxygenation can be confirmed by pulse oximetry or measurement of Pao2 .Caution must be used in patients with increased PVR because the addition of nitrous oxide to volatile anesthetics may exacerbate increased resistance of the pulmonary vasculature.
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17. In addition, nitrous oxide is contraindicated in situations in which it has the potential to expand within a closed air space, such as during closure of a thoracotomy after pneumonectomy when there is no thoracostomy drain.
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18. To decrease requirements for volatile anesthetics and facilitate controlled ventilation of the lungs, a nondepolarizing neuromuscular blocking drug is usually administered; these drugs also improve surgical exposure by maximizing mechanical separation of the ribs.
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19. Ketamine may likewise be useful for induction of anesthesia in patients undergoing emergency thoracotomy associated with hypovolemia (blunt trauma, gunshot wounds, and stab wounds).
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20. For effective postoperative pain control, a thoracic epidural catheter is placed preoperatively while the patient is sedated but conscious. Patients undergoing thoracotomy usually have an intra-arterial catheter in place to permit continuous monitoring of systemic blood pressure and periodic measurement of arterial blood gases and pH. A central venous catheter may be helpful for guiding intravenous fluid replacement.
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21. Transesophageal echocardiography is also a useful intraoperative monitor for myocardial wall function, cardiac valve function, and any myocardial wall motion abnormalities that may reflect myocardial ischemia. A catheter should be inserted into the bladder of patients who are expected to undergo long operations associated with alterations in blood volume and thus the infusion of large amounts of intravenous fluids.
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22. Separation of the Lungs (One-Lung Anesthesia)
Separation of the lungs is perhaps the most important anesthetic procedure in patients undergoing thoracic surgery . Separation of the lungs permits intraoperative one- lung ventilation, which greatly facilitates the surgical procedure. Double-lumen endobronchial tubes (DLTs) and bronchial blockers (BBs) with single lumen endotracheal tubes enable anatomic isolation of the lungs and facilitate lung separation.
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24. ANATOMIC CONSIDERATIONS
The tracheobronchial anatomy should first be assessed by reviewing preoperative radiologic studies. In addition, bronchoscopy is helpful immediately before surgery for detecting abnormal anatomy that may complicate lung separation. For example, a markedly distorted carina or a proximal endobronchial tumor may necessitate fiberoptic guided endobronchial intubation.
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25. Tracheobronchial dimensions in general are approximately 20% larger in men than women. The right main bronchus diverges from the trachea at an angle of 25 degrees, whereas the left main bronchus diverges at 45 degrees. The right main bronchus is shorter but wider than the Left.
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26. Tracheobronchial anatomy. (Right main-stem bronchus length, 1. 8 ±0
Tracheobronchial anatomy. (Right main-stem bronchus length, 1.8 ±0.8 cm; width, 1.6 ±0.2 cm. Left mainstem bronchus length, 4.8 :I:0.8 cm; width, 1.3 :I:0.2 cm.)
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27. Although there is variation in tracheal and bronchial width in the population, within individual patients a significant correlation between tracheal and bronchial width has been determined (bronchial diameter is predicted to be 0.68 of tracheal diameter).
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28. Based on these dimensional relationships, a left-sided DLT is preferred because uniform ventilation to all lobes will most likely be achieved, and measurement of tracheal width from a posteroanterior chest roentgenogram can help select the size of a left-sided DLl
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29. LEFT-SIDED DOUBLE-LUMEN TUBE
Placement of a left-sided DLT is the most reliable and widely used approach for endobronchial intubation in one-lung ventilation . Several manufacturers such as Mallinckrodt, Rusch, and Sheridan produce clear, disposable polyvinyl chloride tubes with high-volume, low pressure tracheal and bronchial cuffs. In general, a 35- or 37-French tube can be used for most women and a 39- French tube for most men.
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31. Insertion Technique for Placement of a Left-Sided Double-Lumen Tube
Endobronchial intubation is usually accomplished by direct laryngoscopy after induction of general anesthesia and neuromuscular blockade. The left-sided DLT tube is held so that the distal curve faces anteriorly while the proximal curve is to the right. The bronchial cuff is inserted through the vocal cords, and the stylet is removed. Next, the tube is rotated 90 degrees to the left (directing the bronchial lumen to the left main stem bronchus). The tube is advanced until moderate resistance to further passage is encountered.
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32. Force should never be used during advancement of the tube; resistance usually indicates impingement within the main stem bronchus. An estimate of the appropriate depth of placement of the DLT can be based on the patient's height.
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33. The average depth of insertion referenced to the corner of the mouth is 29 cm for patients 170 cm tall, and for each 10-cm increase or decrease in height, the average depth of placement correspondingly changes by 1 cm. Correct DLT position must be confirmed by fiberoptic bronchoscopy .
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35. Dependence on physical examination to confirm proper position of a left-sided DLT is not reliable, with fiberoptic assessment showing mal positioning in 20% to 48% of placements considered to be appropriate on the basis of auscultation.
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36. Fiberoptic Visualization of a Left-Sided Double-Lumen Tube
A 3.6-mm fiberscope is initially passed through the tracheal lumen. Correct position of the DLT is confirmed by visualization of the carina, a nonobstructed view of the right main stem bronchus, and the blue bronchial cuff below the carina
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38. In addition, the line encircling the tube should be visualized
In addition, the line encircling the tube should be visualized. This line is 4 cm from the distal lumen, and it should ideally be positioned at or slightly above the carina. Fiberoptic visualization through the bronchial lumen reveals the bronchial carina and the left lower and upper lobes .
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40. Tube Malpositioned Left-Sided Double-Lumen
A malpositioned left-sided DLT may occur during initial placement, after surgical positioning, or during surgery. A mal positioned tube is usually detected by clinical signs and changes in lung mechanics. During initiation of onelung ventilation, peak inspiratory airway pressure should increase by approximately 50% when compared with two lung ventilation at the same tidal volume.
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41. when the DLT is malpositioned, peak inspiratory airway pressure will increase by approximately 75%. Two algorithms define three types of mal positioned left- sided DLTs .
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43. RIGHT-SIDED DOUBLE-LUMEN TUBE
The short and variable distance of the right upper lobe orifice from the carina makes the use of a right-sided DLT undesirable for most procedures requiring lung separation. A small change in the position of the tube results in inadequate lung separation or collapse of the right upper lobe, or both.
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44. Nevertheless, in some situations it is best to avoid intubation of the left main stem bronchus (obstructed by tumor, disrupted after trauma, distorted secondary to a thoracic aortic aneurysm). Right-sided DLTs aredesigned to incorporate a separate opening in the bronchial lumen to allow ventilation of the right upper lobe .
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46. Confirmation of correct right-sided DLT position by physical examination alone results in a 90% chance of malposition, with most being too deep. Proper positioning of a right-sided OLT must include fiberoptic guidance.
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47. Bronchial Blockers
Lung separation can also be effectively achieved with a single-lumen endotracheal tube and fiberoptically guided placement of a BB.The BB technique can be useful if postoperative ventilation will be required because it eliminates the need to exchange the DLT for a single-lumen tube. Using a BB is especially helpful when managing a difficult airway.
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48. For example, in patients requiring an awake, fiberoptic intubation where DLT placement may be impossible, use of a BB may be the only practical approach to lung separation. Confirmation of proper BB position should include fiberoptic bronchoscopy.
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49. UNIVENT BRONCHIAL BLOCKER TUBE
The Univent BB tube has two compartments: a large, main lumen for conventional air passage and a small lumen embedded in the anterior wall of the endotracheal tube that permits passage of the movable BB .
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51. The BB is a relatively stiff catheter that has an internal channel measuring 2 mm through which oxygen may be insufflated. After tracheal intubation with the BB retracted, initial positioning is accomplished by the tube rotation method. Rotating the tube to the right or left positions the BB so that it may be advanced into the corresponding main stem bronchus.
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52. Fiberoptic visualization should be used to confirm appropriate main stem intubation and to guide the depth of insertion. For right sided placement, the BB should be positioned so that inflation of the cuff will cause partial herniation into the right upper lobe . .
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54. For left-sided placement, the BB should be inserted deep into the main stem bronchus to minimize dislodgment into the trachea with surgical manipulation .
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56. GAS EXCHANGE DURING THORACOTOMY AND ONE-LUNG VENTILATION
The intrapulmonary distribution of blood flow is regulated by gravity, lung volume, and regional PVR. As a result, in the lateral decubitus position, the dependent lung receives a greater proportion of the cardiac output (about 60%).
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57. During thoracotomy and mechanical ventilation, the proportion of tidal ventilation to the operated (nondependent) lung increases because lung and thorax compliance in this hemithorax is greater once the chest is opened.
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58. In contrast, the dependent lung has low compliance and low ventilation per unit lung volume. Furthermore, the dependent lung is compressed because of pressure from the abdominal contents and the weight of the mediastinum, which is no longer offset by the subatmospheric pressure in the non dependent hemithorax. These factors, combined with the inhalation of soluble gases, promote atelectasis in the dependent lung.
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59. Thus, the nondependent lung is well ventilated but poorly perfused (high ventilation-to-perfusion [V/Q] ratio), and the dependent lung is well perfused but poorly ventilated (low V/Q ratio). These V/Q imbalances lead to altered pulmonary gas exchange.
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60. Disadvantages of One-Lung Anesthesia
The major disadvantage of one-lung anesthesia is the introduction of an iatrogenic right-to-Ieft intrapulmonary shunt by the continued perfusion of both lungs while only one lung, the dependent lung in the lateral decubitus position, is ventilated. After the initiation of one-lung ventilation, Pao2 decreases progressively during the first 20 minutes and remains relatively constant thereafter.
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61. MANAGEMENT OF ONE-LUNG VENTILATION
An FI02 of nearly 1.0 is recommended during one-lung ventilation; nevertheless, arterial hypoxemia cannot be completely prevented .
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63. In approximately 25% of patients, Pa02 is ≤80 mm Hg, and in 10% of patients, ≤60 mm Hg.The dependent lung should be ventilated with tidal volumes of 8 to 10 mL/kg. Ventilation with tidal volumes of 5 to 7 mL/kg may promote atelectasis in the dependent lung.
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64. The respiratory frequency is adjusted to maintain minute ventilation at the same level as during two-lung ventilation; Paco2 will be maintained at similar or slightly lower levels than those observed during two- lung ventilation
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65. Approaches to Improve Oxygenation during One-Lung Ventilation
Proper positioning of the DLT should be confirmed with the fiberscope because dislodgment of the tube is not uncommon after positioning of the patient for surgery and again after surgical manipulation. The most effective approach to improve oxygenation is the application of 5 to 10 cm H20 continuous positive airway pressure (CPAP) to the nondependent lung.
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66. This level of CPAP results in minimal lung inflation and generally does not interfere with surgery. Nevertheless, discontinuing CPAP before lung stapling may be required to minimize postoperative air leaks. CPAP applied to the operative lung may not be helpful in certain conditions, such as thoracoscopy, bronchopleural fistula, sleeve resection, or massive pulmonary hemorrhage.
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67. Because atelectasis in the dependent lung is an important factor causing arterial hypoxemia during one lung ventilation, ventilation strategies applied to the dependent lung are often intended to improve arterial oxygenation. Initially, an alveolar recruitment maneuver (sustained increase in peak pressure [40 cm H20] for 5 to 10 breaths) may result in increased Pao2 because of recruitment and expansion of atelectatic alveoli.
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68. If the improvement in Pao2 is not sustained, selective application of PEEP to the dependent lung is then initiated. In many circumstances, PEEP applied to the dependent lung may result in decreased Pao2 because of the increased PVR of the dependent lung, which then diverts blood flow to the nondependent and atelectatic lung.
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69. CONCLUSION OF SURGERY
Hyperinflation of the lungs is an important maneuver to remove air from the pleural space at the conclusion of thoracic surgery. Furthermore, alveoli incised during segmental resection of the lungs continue to leak air into the pleural space, thus necessitating placement of chest tubes to minimize the air leak and promote continued expansion of the lung.
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70. Chest tubes should be set to continuous suction and must not be allowed to kink because sudden increases in intrathoracic pressure, as with coughing, may increase the air leak and cause tension pneumothorax if air cannot escape.
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71. . Excessive negative pressure can cause hypotension by shifting the mediastinum and compromising cardiac output.
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72. The trachea may be extubated when adequacy of spontaneous ventilation is confirmed and protective upper airway reflexes have returned. In otherwise healthy patients, extubation of the trachea may be performed at the conclusion of surgery, especially if pain relief (thoracic epidural analgesia) has been instituted
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73. If mechanical ventilation of the lungs must be continuedIf mechanical ventilation of the lungs must be continued into the postoperative period, it will be necessary to replace the DLT with a single-lumen tube.
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74. POSTOPERATIVE PULMONARY COMPLICATIONS
Postoperative pulmonary complications after thoracic surgery are often characterized by atelectasis, followed by pneumonia and arterial hypoxemia.The severity of these complications parallels the magnitude of decrease in vital capacity and functional residual capacity. Presumably, decreases in these lung volumes interfere with the generation of an effective cough, as well as contribute to atelectasis.
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75. The net effect is decreased clearance of secretions from the airways and lungs leading to pneumonia and arterial hypoxemia. In addition, thoracotomy is known to produce intense postoperative pain as a result of skeletal muscle transection and rib removal during surgery.
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76. Pain Management
Pain decreases respiratory effort, which results in atelectasis, contributes to development of the stress response with increased sympathetic nervous system activity, and increases cardiac morbidity. Thoracic epidural analgesia offers a unique opportunity for the anesthesiologist to improve postoperative recovery after thoracotomy.
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77. By delivering local anesthetics and opioids to a limited dermatomal distribution, thoracic epidural analgesia results in profound segmental analgesia, improved pulmonary function, earlier extubation of the trachea, and prompt mobility in the postoperative period. In addition, in patients with coronary artery disease, thoracic epidural analgesia may provide myocardial protection as a result of decreased sympathetic nervous system activity.
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78. MEDIASTINOSCOPY
Mediastinoscopy is often performed before thoracotomy to establish the diagnosis or resectability of lung carcinoma. Hemorrhage and pneumothorax are the most frequently encountered complications of this procedure. If a thoracotomy is not subsequently performed, it is important to maintain a high index of suspicion for pneumothorax in the immediate postoperative period.
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79. Positive-pressure ventilation of the lungs during mediastinoscopy is recommended to minimize the risk for venous air embolism. The mediastinoscope can also exert pressure against the right subclavian artery and cause loss of a pulse distal to the site of compression and an erroneous diagnosis of cardiac arrest
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80. Likewise, unrecognized compression of the right carotid artery has been proposed as an explanation for the postoperative neurologic deficits that may occur after this procedure.
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81. Bradycardia may occur during mediastinoscopy and is due to stretching of the vagus nerve or trachea by the mediastinoscope. It is treated by repositioning the mediastinoscope, followed by the intravenous administration of atropine if the bradycardia persists
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82. THORACOSCOPY
Thoracoscopy is the insertion of an endoscope (thoracoscope) into the thoracic cavity and pleural space for the purpose of obtaining a lung biopsy and for the diagnosis of pleural disease. This procedure may be performed with local anesthetic infiltration or intercostal nerve blocks which also anesthetize the parietal pleura.
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83. The addition of a stellate ganglion block helps suppress the cough refle. If general anesthesia is used, lung separation with a DIT is preferred because positive-pressure ventilation that includes both lungs would interfere with visualization.
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