ETT, endotracheal tube, FFB, flexible bronchoscope, HFJV, high-frequency jet ventilation
Symptomatic obstruction of the central airways (trachea, carina, main bronchi) can be the result of a variety of benign and malignant processes (Table 1).
Bronchoscopic interventions to relieve central-airway obstruction include surgical resection or core-out, Nd-YAG laser ablation, balloon dilation, brachytherapy, cryotherapy, photodynamic therapy, and airway stenting. 1 This review focuses on airway management during bronchoscopic procedures for central-airway obstruction.
ANESTHESIA FOR BRONCHOSCOPIC PROCEDURES
Every patient must have a full preoperative medical assessment. Pertinent information is obtained from the medical history, physical examination, discussions with the endoscopist, diagnostic imaging studies, and pulmonary function testing. The foremost concern is the nature and degree of the airway disease. Many patients have had serial procedures, and past medical records can provide information about airway access, previous anesthetic management strategies, and complications. It is important to note what size endotracheal tube (ETT) and bronchoscope have been used for prior procedures.
Patients may be experiencing respiratory distress with dyspnea, coughing, and wheezing. Inspiratory stridor suggests extrathoracic airway obstruction whereas expiratory stridor may be the result of intrathoracic obstruction. Many patients also have underlying acute and chronic pulmonary disease. Bronchospasm and other reversible lung conditions should be treated before bronchoscopy.
Potential problems with tracheal intubation must be evaluated. No single test is completely accurate in predicting intubation difficulties. Many attempts have been made to identify risk factors. 2,3 Patients in whom the posterior pharyngeal wall cannot be visualized below the soft palate and who have a short neck are usually more difficult to intubate than patients with normal anatomy. 4 The ability to open the mouth adequately and to extend the neck fully may also determine the ease of tracheal intubation and whether a rigid bronchoscope or a flexible bronchoscope (FFB) can be used for the procedure.
The location, size, and extent of the mass and/or the degree of airway obstruction should be established accurately preoperatively if possible. Conventional radiography may not be accurate. Chest computed tomography and/or magnetic resonance studies should be performed. 5 This information can help determine what size ETT to use, how far that tube may be safely advanced, or whether an ETT can be used at all.
A dynamic flow–volume loop study can differentiate between variable or fixed intra-and extrathoracic airway obstructions . With a variable extrathoracic obstruction there is flow limitation and a plateau during inspiration, whereas with a variable intrathoracic obstruction the reverse occurs and there is limitation of airflow during expiration. 6 With a fixed intra-or extrathoracic obstruction (e.g., tracheal stenosis), the plateau and limitation of airflow is seen in both the expiratory and inspiratory flow–volume loops. This information is important to the anesthesiologist because the nature of the airway obstruction may determine the method of anesthesia induction and airway management.
Spirometric testing may also be helpful in assessing pulmonary function as well as the ability to reverse bronchospasm pharmacologically. If possible, an arterial blood gas reading with the patient breathing room air should be obtained. The presence of arterial hypoxemia and hypercarbia increases the likelihood of anesthetic management problems during or after the procedure.
Many patients with a malignancy may have undergone chemotherapy or radiation therapy. These therapies may be associated with systemic toxicity, cardiomyopathy, pulmonary damage, and additional alteration of airway anatomy.
Sedative premedication should only be considered for the very anxious patient because of the potential for hypoventilation and additional airway compromise. Patients with marked airway obstruction should not be sedated or left alone in an unmonitored environment.
An anticholinergic drying agent (atropine, glycopyrrolate) may be helpful, especially in the presence of excessive airway secretions which can impair the effectiveness of topical anesthesia. A drying agent reduces the need for frequent suctioning during the procedure. This is important because suctioning may interfere with gas exchange, causing hypoxemia.
Whenever bronchoscopy is performed under general, regional, or monitored anesthetic care, the American Society of Anesthesiologists standards require that qualified anesthesia personnel be present to monitor continuously oxygenation, ventilation, circulation, and temperature (Table 2).
The method of achieving airway control depends on the nature of the patient's airway disease. One can proceed with an “awake” intubation under topical anesthesia, an inhalation anesthetic induction preserving spontaneous ventilation, or a routine induction using intravenous agents and a muscle relaxant to facilitate ETT placement.
One must always be careful when advancing the ETT down the trachea because it can cause bleeding and aggravate an intraluminal obstruction. Fiberoptic intubation and placement of the ETT under direct vision is the technique of choice for many patients with central airway lesions.
An inhalation anesthetic induction with the patient breathing sevoflurane can avoid the need for a muscle relaxant and is indicated in patients with a variable intrathoracic obstruction caused by an anterior mediastinal mass. For fixed obstructions, an intravenous anesthetic induction using muscle relaxants is more appropriate. The special anesthetic considerations for patients with anterior mediastinal tumors are reviewed elsewhere. 7
Choice of Anesthetic
Bronchoscopy normally poses special problems for the anesthesiologist because the airway must be shared with the endoscopist. These problems are magnified in a patient with an obstructed airway. The endoscopist requires good visibility and adequate space for instruments, whereas the anesthesiologist is concerned about gas exchange and hemodynamic stability. The diversity of anesthetic techniques used for these procedures means that no single technique meets all requirements for all patients.
Local anesthesia plus intravenous sedation is often used but may be a poor choice if patient movement could jeopardize the procedure. Many procedures require an immobile field for precise airway measurement or for accurate direction of a laser beam. The need for the patient to be completely still mandates general anesthesia and often the use of a muscle relaxant. Short-acting neuromuscular relaxants (succinylcholine, mivacurium) should be used, and paralysis must be fully reversed before tracheal extubation. 8
Many general anesthetic techniques combine inhalational and intravenous agents. All commonly used inhalation anesthetic agents (halothane, isoflurane, sevoflurane, desflurane) have bronchodilatory effects that may be helpful because of the frequent presence of reactive airway disease. Intravenous agents (barbiturates, propofol, opioids, ketamine) can maintain anesthesia during suctioning, bronchial dilatation, or stenting when ventilation with an inhalational agent is interrupted. Whatever anesthetic technique is used, a fast-acting intravenous agent should be available in case the patient moves. Only short-acting opioids (remifentanil, alfentanil) should be used. Because there is minimal pain after these procedures and postoperative respiratory depression is dangerous, long-acting opioids (morphine, Dilaudid, meperidine) are avoided.
Once the trachea is intubated there is the possibility that the airway distal to the ETT can collapse or remain obstructed. A rigid bronchoscope should always be available to reestablish a patent airway.
Method of Ventilation
Several techniques can be used for ventilation during rigid and flexible bronchoscopy, including spontaneous breathing, intermittent positive-pressure ventilation, use of the Sanders injection system, and high-frequency jet ventilation (HFJV). 9 For FFB, intermittent positive-pressure ventilation through an ETT is the usual choice. The FFB is placed through the self-sealing diaphragm of a bronchoscope adaptor attached to the ETT. The FFB within the ETT reduces the available cross-sectional area and increases resistance to gas flow. An ETT with an internal diameter of at least 8.0 mm is required for adults.
The rigid ventilating bronchoscope incorporates a side-arm adaptor that is attached to the anesthetic breathing system. Occlusion of the proximal end of the bronchoscope with an eyepiece allows controlled ventilation through the lumen of the bronchoscope. There is always a gas leak around the bronchoscope, and ventilation is interrupted whenever the eyepiece is removed. Continued ventilation with an anesthetic agent while the eyepiece is removed will result in gas inhalation by the endoscopist.
HFJV allows uninterrupted ventilatory support during rigid bronchoscopy. High-frequency positive-pressure ventilation through catheters with internal diameters as small as 2.0 mm can provide safe levels of oxygenation as long as an adequate expiratory passage is present. 10 A technique using a 14-Fr nasal insufflation catheter with HFJV to avoid an ETT has been used for FFB placement of tracheal stents. 9 In cases of tracheal obstruction, the HFJV catheter is placed beyond the stenosis.
The Sanders technique uses the Venturi principle to deliver positive-pressure ventilation through an open rigid bronchoscope. Intermittent bursts of high-pressure oxygen are delivered through a cannula attached to the proximal end of the bronchoscope. The jet of oxygen entrains large volumes of room air, and adequate tidal volumes can be achieved. This technique is particularly useful because it allows the endoscopist to work through the open rigid bronchoscope without interruptions of ventilation. Paco2 levels are generally acceptable, and adequate oxygenation is maintained. 11
Bronchoscopic airway procedures require that the patient remain adequately anesthetized until the very end of the procedure. The time required for the return of airway reflexes, complete reversal of muscle relaxant, and emergence from anesthesia depends on the agents used and the duration of the anesthesia.
Airway patency may actually worsen as the patient recovers from anesthesia. Edema in the upper airway may manifest itself once the bronchoscope is removed. During emergence, coughing may increase bleeding. If a rigid bronchoscope has been used, a decision must be made whether to replace it with an ETT.
At the completion of the procedure the patient should be fully awake. If the patient is obtunded and not breathing adequately, or if the airway has been traumatized and airway patency is a concern, the trachea should remain intubated. A tube exchanger can be placed in the trachea through the rigid bronchoscope or the ETT before extubation. If reintubation becomes necessary, the tube changer is used as a guide for placement of a new ETT. 12
Although most patients have their trachea extubated at the completion of the bronchoscopic procedure, the anesthesiologist must be prepared for emergency reintubation and have all the necessary airway equipment available. The endoscopist and the bronchoscopic equipment should also be available until the patient has fully emerged from anesthesia and airway patency has been ensured.
All patients should receive supplemental oxygen after extubation, during transport to, and while in the postanesthesia care unit. Stridor after the procedure may require treatment with humidified oxygen, nebulized epinephrine, steroids, or even reintubation.
The anesthesiologist must be prepared to deal with complications while working in a confined, unfamiliar environment. The complication rate depends on the operator's skill, the method of bronchoscopy, the anesthetic technique, the condition of the patient, and the location and extent of the tumor. 13
Even in patients without airway pathology, pulmonary function is decreased immediately after bronchoscopy. The decrement in postoperative pulmonary function may be the result of premedication with antisialagogues and sedatives, the topical anesthetic, or the result of mechanical obstruction by the lesion. 14
Complications of bronchoscopy can include laryngeal and bronchial spasm. Damage to teeth is common. Direct trauma to the airway can cause bleeding, edema, and tumor fragmentation. Mucosal perforation or barotrauma may lead to subcutaneous emphysema and tension pneumothorax. There is always a possibility of massive hemorrhage with the need for emergency thoracotomy. 15 For procedures with a very high likelihood of serious complications, an operating room should be available and prepared even when the actual procedure is performed at a distant location such as the radiology suite.
Cardiovascular instability (hypertension, hypotension, arrhythmias) is common. Bradycardia occurs as a vagally mediated response to insertion of the bronchoscope but may be avoided with the use of an anticholinergic agent. Light anesthesia with the release of catecholamines, hypoxia, and hypercapnia all contribute to arrhythmias.
Complications associated with bronchoscopic relief of airway obstruction include hypoxemia, bleeding, bronchospasm, and perforation of the airway.
There may be marked resistance to ventilation from a misplaced stent or dislodged tumor material. 16 Aspiration of resected material is also a possibility. A postoperative chest radiograph should be obtained because airway instrumentation carries the risk of pneumothorax or segmental lung collapse. Delayed massive hemoptysis may occur after any of these therapies if pulmonary artery–bronchial fistulae develop. 17 A rigid bronchoscope and equipment for tracheostomy or cricothyroidotomy should be readily available for airway emergencies.
SPECIAL PROCEDURES FOR CENTRAL-AIRWAY OBSTRUCTION
A metal or silicone rubber stent in the trachea or bronchus can be an effective means of providing structural support for select patients with intraluminal obstructions, malacia, or extrinsic airway compression. 16 Successful stenting can provide immediate, symptomatic relief of life-threatening dyspnea.
Airway stents are particularly useful after pulmonary transplantation complicated with graft rejection or infection, 18 after tracheobronchial injury, 19 and for intrinsic tumors of the airways. 20 Stenting procedures can be performed in adults and children. 21 Although alternative therapies (balloon dilation, Nd-YAG laser ablation, brachytherapy, cryotherapy) can be used for intrinsic obstructions, only stenting is effective for malacia and extrinsic airway compression. Stents are also used for esophageal airway fistulae.
Most patients experience immediate symptomatic improvement. Mean forced vital capacity, mean peak expiratory flow, mean forced expiratory volume in 1 second, and Pao2 all increase after successful stent placement. 22,23 Patients with airway obstructions requiring ventilatory support can be separated from the ventilator and have their trachea extubated after the stenting procedure. 24,25
Expandable metal stents are easier to insert and have a wider internal lumen than silicone stents. Metal stents do not impair the drainage of sputum because ciliary movement is not interrupted. Expandable metal stents are indicated for unresectable malignant airway disease because, once placed, they are considered permanent. Because they are so difficult to remove they are also less likely than silicone stents to become displaced and migrate distally. 26 Their flexibility allows them to be bent so they conform better to tortuous airways than rigid silicone stents.
Over a period of just a few weeks the metal stent is incorporated into the airway wall and its mesh becomes covered with mucosa. Therefore, metal stents are only temporarily effective for transbronchial stenosis resulting from intraluminal tumor or granulation tissue because both can eventually grow between the wire mesh. 27
A metal stent can be placed under topical anesthesia with or without intravenous sedation. If an immobile patient is essential for airway measurement, dilation, and accurate stent positioning, then general anesthesia with or without a muscle relaxant is a better choice.
Tracheostomy may not be feasible through a metal tracheal stent. However, because the stainless steel stent is mesh with large spaces between the wires, cricothyroidotomy may be possible. Stent displacement, mucus impaction, and granulation tissue formation are potential long-term complications.
Silicone stents are inserted via a rigid bronchoscope under general anesthesia. They are not permanent and can be removed or displaced easily, thus they are used in situations when stenting is intended to be temporary. A silicone stent can be removed when the stenosing airway disease subsides, so they are indicated for obstruction resulting from inflammation and infection. 28 The anesthesiologist must be aware that the position of a previously placed silicone stent, especially one in the trachea, may change during subsequent tracheal intubation.
Nd-YAG Laser Therapy
Nd-YAG laser therapy is used for resection of airway malignancies 29 or granulation tissue. 30 The laser can tunnel through a complete obstruction or widen a narrowed lumen, providing immediate relief of symptoms. 31
The Nd-YAG laser is conducted through a flexible quartz monofilament that can be passed down either an FFB or a rigid bronchoscope. The laser penetrates deeply and destroys tissue by a coagulation–vaporization sequence. The Nd-YAG laser photocoagulates the margins of the tumor, and then sections of the devascularized tumor must be removed physically from the airway. A continuous 3-L/min flow of air is passed simultaneously through a co-axial Teflon sheath to cool the fiber tip and keep it free of debris.
A rigid bronchoscope is preferred because it provides better visibility and better suctioning conditions, and allows easier retrieval of blood, mucus, and tumor debris. 32 A rigid bronchoscope also maintains the patency of the airway. Unlike the FFB, a rigid metal bronchoscope is nonflammable. 33 However, the metal can reflect a laser beam, resulting in tissue damage.
An FFB can reach distal airways beyond the reach of a rigid bronchoscope. The Nd-YAG laser can be passed down an FFB directly into the airway in an awake but sedated patient. However, if the patient moves, the laser beam can be misdirected, resulting in serious complications.
General anesthesia including a muscle relaxant is usually a better choice than topical anesthesia and intravenous sedation. 34 For Nd-YAG therapy, a conventional plastic ETT with an internal diameter of at least 8.0 mm is needed to accommodate the FFB and still allow sufficient space to ventilate the lungs. The laser must be fired beyond the tip of the tube to avoid ignition of the tube material. Saline inflation of the airway's cuff may reduce the risk of fire from a misaimed laser.
It is important to avoid using nitrous oxide because that gas supports combustion. An air–oxygen mixture limiting the Fio2 to less than 0.4 should be used. The problems of oxygenating a patient with severe airway obstruction are compounded by this requirement to ventilate with such a low Fio2. A premixed helium–oxygen mixture (Heliox; 70%/30%) has been used to prevent combustion with the carbon dioxide laser. 35 In addition to protecting against fire, helium may improve ventilation beyond an obstructing airway lesion because its density is less than that of nitrogen. Helium is expensive, not readily available, and may interfere with oxygen analyzers in the system and give erroneous values.
Whichever anesthetic technique (sedation or general anesthesia) is used, there is usually an increase in Paco2 and a decrease in pH and Pao2 after Nd-YAG procedures. 36 Because the laser beam can pass through the cornea and cause retinal damage, special blue–green eyeglasses are required to protect the eyes. Some colored anesthesia monitor displays are difficult to read with these glasses. The patient's eyes should be covered with moist pads. 37 The windows of the operating room or bronchoscopy suite should be covered and there should be a sign on the outside of the door warning that a laser is in use. The plume (products of the tissue combustion) released during laser resection can be noxious to breathe or even hazardous to the health. 38,39 Effective smoke evacuation can help control deleterious effects.
With the Nd-YAG laser only the surface of the affected tissue is visibly changed, but underlying edema formation can result in additional obstruction or hemorrhage hours after laser therapy. 40 Prophylactic dexamethasone or methylprednisolone is sometimes recommended to reduce tissue swelling.
Bleeding usually is minimal and can be controlled by epinephrine-soaked gauze pledgets. However, if the laser strikes a vascular structure, severe hemorrhage can result. 41 Major bleeding complications occur most often when a main-stem bronchus is totally occluded. Because the direction of the lumen is unknown, perforation of the wall of the bronchus is more likely to occur with perforation of vessels. 42 Airway perforation may result in tracheo-or bronchoesophageal fistulae and pneumothorax. 43
Balloon Dilation of the Airway
Balloon dilation is a safe and effective palliative procedure for airway narrowing in adults, 44 and for congenital and acquired stenosis of the trachea and bronchi in children. 45 A balloon catheter is threaded over a guide wire and is positioned across the stenotic airway. 46,47 Under direct vision with an FFB or a rigid bronchoscope, the balloon is inflated for 30 to 120 seconds. Repeat inflation–deflation sequences are performed if airway narrowing persists. Usually there is immediate improvement, with an increase in airway dimensions and relief of symptoms. 47 However, improvement is usually temporary and many patients require serial dilatations, placement of an airway stent, or laser therapy. 46
The actual physical dilation is very stimulating, and the patient may cough vigorously. When performed under general anesthesia, either a short-acting muscle relaxant should be used or a rapid-acting intravenous anesthetic should be available to control coughing.
Cryotherapy is another bronchoscopic procedure for upper airway obstruction. Benign obstructions are first dilated with a balloon, followed by cryotherapy using nitrous oxide as a cryogen applied through an FFB.
As an alternative to the Nd-YAG laser, cryotherapy is inexpensive and safe for the operator and other members present. There is no danger of bronchial wall perforation or endobronchial fire. 48
Cryotherapy is usually performed under topical anesthesia and conscious sedation in a bronchoscopy suite without the presence of an anesthesiologist. The anesthesiologist may be called for an acute airway crisis.
Bronchoscopic brachytherapy is the direct application of a radioactive isotope into a tumor bed within the airway using a bronchoscope. A highly localized dose of radiation can be delivered to the tumor while sparing the surrounding healthy tissue. 49 Brachytherapy is effective as a palliative treatment of dyspnea, hemoptysis, intractable cough, postobstructive atelectasis, and pneumonia from tracheal and bronchial malignancies. 50 Brachytherapy has also been used to relieve benign airway obstruction from hyperplastic tissue when other interventions have failed. 51
Originally the radioactive source was applied directly to the tumor through a rigid bronchoscope. Intraluminal placement of the radioactive substance is now performed through a polyethylene after-loading catheter using an FFB. 52
Before commencing phototherapy, a hematoporphyrin derivative is administered intravenously 3 to 5 days before the start date. 53 When a laser light is shown through an FFB, target neoplastic tissue will fluoresce. In the presence of a sensitizer, selective photon absorption by the tumor occurs, and the concomitant use of a laser beam results in a chemical reaction that causes tumor cell death whereas normal tissue is not harmed.
Combustion is not a problem, so the lungs can be ventilated with 100% oxygen. Delayed complications associated with phototherapy include bleeding and airway obstruction from tissue necrosis.
The patient with central-airway obstruction undergoing an endoscopic procedure is a challenge to the anesthesiologist. One must be familiar with the basics of anesthesia for flexible and rigid bronchoscopy, and also with the special considerations of each of the different therapeutic interventions currently used in treating central-airway obstruction.
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