Airway Anatomy and Nomenclature

The basic pulmonary function of gas exchange occurs at the level of the alveolus, located in the distal acinus beyond respiratory bronchioles, but for the purpose of the bronchoscopist, it is more important to recognize the more proximal airway divisions. Distal to the trachea and the mainstem bronchi, the lobar bronchus defines the division of the lobes, and the segmental bronchi the pulmonary lobules (Fig. 75-1). There are thus three lobes in the right lung, with normally ten segmental lobules, although there may be some anatomic variants. In the left lung, the left upper lobar segments and the lingular subsegments come off the same left upper lobe bronchial division, which also explains why resection of the left upper lobe often requires inclusion of the lingular, and vice versa. Because of the anatomic divisions, the left lung is often divided into nine segmental lobules, although here again there are anomalies, and the bronchoscopist should be familiar with the variations. Because of the location of the heart, the right lung usually accounts for 55% to 60% of the total lung parenchyma, and the left lung the smaller remainder. This information becomes important in estimations of residual pulmonary function after a planned lobar resection or pneumonectomy.

Figure 75-1. Tracheobronchial schema. Gen, generation.

An additional source of frequent confusion in the naming of the segmental and subsegmental bronchi has to do with the frequent but incorrect interchange of the terms generation and order of the bronchial segments. Standard nomenclature of the human airways denotes the trachea as the zero-generation airway, with each of the right and left mainstem bronchi being the first generation, lobar bronchi the second generation, lobar segmental bronchi the third generation, and so forth. Conversely, order of airway segment refers to the retrograde counting from the “lobular bronchiole,” which is the first airway segment with a diameter of less than 0.7 mm. Hence, more central airways of a larger dimension actually have a higher order.^1,² However, given the uneven segmentation and subsequent diminution of airway calibers, there is far less uniformity of division of airway in the different lobes, and lobules narrow down to 0.7 mm. Hence, the standard textbook description of the 0.7-mm lobular bronchiole located in the 10th- to 14th-generation bronchi does not match the bronchoscopic findings of airways navigable by a bronchoscope significantly wider than 0.7 mm beyond the number of branchings described previously.²^–⁴ In summary, it is best to use the term generation in the description of sequential airway branching, starting from the trachea. Dr. Shigeto Ikeda,⁵ regarded as the founder of modern fiberoptic bronchoscopy, also developed a detailed system of naming segmental and subsegmental airways branchings, but that topic is beyond the scope of this chapter.

Indications and Preparations for Tracheobronchoscopy

Indications

Indications for tracheobronchoscopy include the evaluation of acute or chronic respiratory symptoms such as hemoptysis, nonresolving and worsening cough, and acute or worsening subacute dyspnea that may be accompanied by wheezing or stridor, pleurisy, chest pain, fever, or other symptoms suggestive of a pulmonary process (Box 75-1). Symptoms may be accompanied by radiographic abnormalities suggesting an endobronchial lesion, extrinsic compression of the airways by a mediastinal or lung mass, or presence of an infiltrate. Patients are often also referred for evaluation of asymptomatic lung or mediastinal masses and nonresolving parenchymal lung infiltrates. Pleural effusions usually lead to evaluation of the pleural fluid; however, effusions most often have an underlying parenchymal pulmonary cause, and a nonresolving effusion without an established cause after thoracentesis or thoracoscopy should prompt an examination for endobronchial obstruction. Bronchoscopy is helpful in assessing the placement of endotracheal tubes, especially in difficult intubation cases or when double-lumen tubes are required. A flexible fiberoptic bronchoscope (FOB) can be used to guide placement of an endotracheal (ET) tube in a difficult airway; in such cases, the ET tube is prepositioned and advanced over the bronchoscope. An FOB can also be used to guide percutaneous tracheostomy. Indications for tracheobronchoscopy in children include suspected foreign body, respiratory distress secondary to tracheomalacia or bronchomalacia, and evaluation of other congenital anomalies. Depending on the findings on radiography or during a diagnostic bronchoscopy, therapeutic interventions may be performed with an FOB to maintain airway patency and improve gas exchange.^6,⁷

Box 75-1 Indications for Tracheobronchoscopy

After consideration of the indication for the procedure, the next steps of planning should include the multimodality team of otolaryngologists, pulmonologists, radiologists, anesthesiologists, nurses, respiratory therapists, “backups” in thoracic surgery and interventional radiology if their services may be needed, and, not least, the patient and family for careful discussion and informed consent.

Radiology

Given the millimeter-range high-resolution and rapid multiplanar reconstruction of the airways achievable with multislice spiral computed tomography (CT) scanners, a preprocedural CT scan can help pinpoint the location and extent of disease and reduce the time spent on exploration in patients with limited cardiopulmonary reserve. A contrast-enhanced CT scan is especially useful to provide the spatial relationship between pathology and vasculature and, hence, to minimize the risk of accidental and potentially life-threatening vascular injury from interventions such as laser or mechanical débridement. Contrast-enhanced atelectatic lung parenchyma can often also indicate whether there is viable lung tissue beyond central obstruction. Three-dimensional measurements of airway stenosis length and diameter facilitate the preselection of balloons for bronchoplasty and of airway stents for maintaining patency in an obstructed airway segment. A thoracic surgeon or interventional radiologist should be consulted before the bronchoscopic investigation of massive hemoptysis, in case the bleeding source can only be identified—but not quelled—by bronchoscopic interventions.

Sedation and Airway Management

Maintaining gas exchange is critical during bronchoscopy, together with the desire of minimizing patient discomfort and anxiety. Some level of sedation, monitoring, and augmentation of oxygenation and ventilation is carried out with the assistance of an anesthesiologist or nursing personnel certified in sedation and airway management. Conscious sedation usually involves intravenous sedation with short-acting benzodiazepines (midazolam is most commonly used) or other anxiolytic agents plus a short-acting narcotic (e.g., fentanyl, meperidine, or morphine sulfate) to help suppress the cough reflex. My colleagues and I also find promethazine (Phenergan) useful in patients who are difficult to sedate or who have a strong gag reflex. The medications are given in measured, small boluses and the patient is appropriately monitored with hemodynamics, cardiac monitors, and pulse oximeters. Not yet routinely used but increasingly available is transcutaneous capnography. Deep sedation with propofol (Diprivan) provides for rapid on-and-off titration of sedation and can be very helpful in some patients who are difficult to sedate. General anesthesia with inhalational anesthetics with or without intravenous sedation provides the greatest control, but this would mandate the use of an ET tube, laryngeal mask airway (LMA) ventilation, rigid endoscopy with side-port ventilation, or a previously placed tracheostomy. It is also contingent on the presence of an anesthesiologist or a nurse anesthetist, who may not be readily available for bronchoscopies performed in endoscopy units separate from the operating rooms.

For patients undergoing bronchoscopy under conscious sedation, topical anesthetics are commonly used to reduce the amount of systemic sedative-narcotics needed to suppress cough, and also to diminish local discomfort in the nasopharynx during the passage of the bronchoscope. Lidocaine and its derivatives are most commonly used and applied topically as a gel to the nasal passage or as a spray to the posterior oropharynx. Solutions with concentrations between 1% and 4% are available, but the operator must pay attention to the total dosage applied because systemic lidocaine toxicities, including inadvertent deaths in healthy research subjects, have been reported when more than 500 to 1000 mg is delivered topically in a single session.⁸ Therefore, except for spraying to the posterior oropharynx, we limit the use of topical lidocaine injected via the operating channel of the bronchoscope onto the vocal cords and airway mucosa to less than 3 to 4 mg/kg total dosage (1% lidocaine has 10 mg of lidocaine per l mL solution). Cocaine is also a very effective topical anesthetic that has the advantage of vasoconstricting the nasal mucosa membrane; it is, however, not generally available for use in the average endoscopy suite.

Miscellaneous medications that can be used in bronchoscopy include atropine or glycopyrrolate in patients with excessive secretions. Chronic bronchitis patients with acute bronchitis and patients with preprocedural problems handling bronchial secretions may be good candidates for parasympathomimetic agents. Caution should be used because such agents can precipitate tachycardia.

Patient Positioning and Route of Bronchoscope Entry

In a patient under conscious sedation with or without a previously placed tracheostomy, a flexible bronchoscope can be introduced with the patient supine or in a sitting position. It is generally easier for the bronchoscopist to be standing at the head of the bed. If a nasal approach is chosen, a cotton swab soaked with a lidocaine solution or gel is used to determine which of the nares permits easier passage. Studies have found shorter and smaller patients to experience greater postprocedural nasal discomfort when the same-sized bronchoscope is used; hence, for such patients, an oral approach may be preferable. Conversely, because of the sharper angulation of the bronchoscope at the posterior oropharynx when introduced orally, patients tend to have a greater gag response; therefore, a more thorough application of topical anesthetics to the posterior oropharynx is recommended. Because of the risk of trauma to the teeth and the instrument being used, a properly secured bite block is mandatory in this approach. For rigid bronchoscopy, although the early pioneers performed the procedure on fully conscious patients placed in a sitting position, the procedure should be carried out with the patient supine and the neck extended. The patient is almost always fully anesthetized with paralysis to facilitate the passage of the rigid bronchoscope. The rigid bronchoscope can most easily be introduced via the oral route. The insertion and maneuvers of the rigid bronchoscope as well as the proper ventilation and anesthesia are discussed later.

Ventilation and oxygenation can be better maintained in a more upright patient under lighter sedation. With a flexible FOB, the approach is made from the front of the patient. The approach via the nares or an oral passage is similar, although the view on the monitor is inverted because of the position of the bronchoscope tip relative to the approach. Once past the vocal cords, the bronchoscope can easily be turned to regain the familiar view with the ventral or anterior surface of the body facing the top.

In patients under deep sedation or general anesthesia, either a flexible FOB or a rigid bronchoscope can be used to examine the airways. For a flexible FOB, gas exchange is maintained with either an ET tube or a laryngeal mask; the latter is usually sufficiently large such that bronchoscope size is not a factor in limiting adequate ventilation and oxygenation. Prior discussion with the anesthesiologist ensures that a sufficiently large ET tube is inserted to permit smooth passage of the bronchoscope. For therapeutic cases using bronchoscopes with a diameter of 6.0 mm or greater, an ET tube of at least 7.5 mm is needed. Additional options are (1) to perform direct suspension laryngoscopy with intermittent ventilation via an ET tube alternating with bronchoscopic examination and intervention and (2) to perform direct suspension laryngoscopy using spontaneous ventilation and passive oxygenation.

To facilitate passage of the flexible bronchoscope, water-soluble lubricants are applied to the sheath of the bronchoscope. Lubricant jelly has the disadvantage of drying rather quickly, leading to stiffness in maneuvering, especially when the scope is introduced nasally. Lidocaine jelly is a good alternative that also provides some local anesthesia. Newer compounds, such as Endo-Lube (Covidien, Mansfield, MA) provide excellent lubrication and are ideal when the bronchoscope has a tight fit through devices such as an ET tube. Its cost may be higher, and caution is necessary to prevent accidental dislodgement of the ET tube from the ventilator because the lubricant also makes the various connections between the ET tube and ventilator circuit slippery. Mineral oil should not be used if at all possible because of the potential of oil aspiration leading to a lipoid pneumonia.

Patient Discussion and Informed Consent

Well-informed and educated patients and families are more likely to be compliant with therapy. In the case of bronchoscopy, especially in patients undergoing conscious sedation, an explanation of the steps helps alleviate the anxiety over the coughing and gagging that can sometimes force premature termination of the procedure. Ancillary diagnostic and therapeutic procedures, especially on hyperemic inflamed or malignant tissue, often lead to bleeding and postprocedural hemoptysis that should taper off. Similarly, a substantial portion (25%-50%) of patients may experience transient postprocedural fever during the first 24 hours. The cause need not be infectious and may be more common after bronchoalveolar lavage (BAL), which can result in surfactant washout. Informing patients of these two possible minor complications can obviate anxious midnight calls to the physician after a procedure. Conversely, patients should also be warned about prolonged bleeding and delayed pneumothoraces that may not be detected immediately after the procedure. Persistent or high spiking fevers, hemoptysis, and worsening dyspnea should prompt the patient to immediately contact a physician, who may perform a reevaluation with radiograph, physical examination, and other laboratory tests, as indicated.

Rigid Bronchoscopy

Rigid bronchoscopy retains certain important advantages over flexible fiberoptic bronchoscopy, including the much larger lumen that affords access to larger instruments, which may be necessary to remove foreign bodies, to provide adequate suction in brisk hemoptysis, to place noncompressible polymeric silicone (Silastic) airway stents, and to use the bronchoscope itself to core out tumors and provide direct tamponade to a bleeding source. Rigid bronchoscopy today is performed almost exclusively in patients under general anesthesia, and rarely with the use of only topical anesthesia and conscious sedation without paralytics. More commonly, intravenous deep sedation, with or without inhalational anesthetics, is used. A variety of ventilatory strategies are used, from intermittent apneic ventilation to spontaneous/assisted ventilation. Oxygenation and ventilation can be provided by tidal volume through a closed system or via an open system with side-port Venturi jet ventilation.

Before insertion of the rigid bronchoscope, either alone or with a telescope lens through it to provide a better distal view, the patient must be examined for neck stability and for any loose teeth or dentures. A shoulder roll may give room for added extension of the neck. With or without a tooth guard to protect the upper teeth, the operator’s left thumb is placed over the upper teeth and the index finger scissors open to lift up the lower teeth of the relaxed jaw. The bronchoscope with the bevel up is then directed midline and almost perpendicularly toward the hypopharynx until the uvula is passed. The operator thereafter slowly levels the bronchoscope angle toward the horizontal, seeking out the epiglottis while lifting the base of the tongue. When the vocal cords are clearly visualized, the bronchoscope is rotated 90 degrees such that the beveled edge can enter the trachea along the length of the vocal cord, thereby limiting trauma to the cords. Once the tip of the rigid bronchoscope is clearly in the trachea, it is rotated back to its starting position with the bevel up. The operator’s left hand and finger positions are maintained to protect the teeth, although it is also necessary to occasionally use the left hand to provide a better seal around the cuffless rigid bronchoscope at the level of the cricoid and thyroid cartilages when ventilation is applied. Because larger operative rigid bronchoscopes with diameters of 11 to 12 mm are now available for insertion of silicone stents, upper airway and vocal cord edema may be a more severe problem at the end of a prolonged procedure; hence careful examination of the cords and hypopharynx is important to avoid postprocedural stridor and upper airway obstruction. With the advent of flexible fiberoptic bronchoscopy, the number of pulmonary teaching programs routinely including rigid bronchoscopy in their training curriculum is falling. Therefore, even though rigid bronchoscopy should be a skill acquired by all bronchoscopists, generally only those being trained in otolaryngology–head and neck surgery, thoracic surgery, or interventional pulmonology generally receive adequate exposure to and practice with this technique.⁹

Flexible Fiberoptic Bronchoscopy

Advances in fiberoptics, illumination, and image capture, including the use of true color-chip charged couple device cameras embedded in the distal tip of the FOB, have greatly improved the imaging capabilities of the FOB. Most new flexible FOBs are now videoscopes with high-resolution true-color rendition of the image captured by the distal chip. The illumination is still delivered via fiberoptic bundles. The improved imaging quality and the ease of recording areas of interest with digital still images or video segments are offset by the cost of these instruments as well as those of the dedicated processor and high-quality video display units. The startup cost of such a setup with two videobronchoscopes is in the $60,000 to $80,000 range. Conventional FOBs, in which the image is relayed via fiberoptic bundles and viewed at the proximal end of the FOB by the eyepiece or connected to a video display, continue to have a role. This is especially true for FOBs used at the bedside or during operations to confirm the position of standard or dual-lumen ET tubes and for the attachment of special illumination and visualization devices, such as during autofluorescent bronchoscopy.

Range of Flexible Bronchoscopes and Special Features

Although there remains the tendency to subdivide bronchoscopes into “adult” and “pediatric” categories depending on their outer diameters, this distinction is arbitrary. Because bronchoscopists venture more peripherally with FOBs to sample focal lesions, and more interventional procedures via a flexible FOB are performed in the pediatric population, it makes more sense to describe the bronchoscopes and leave their judicious application to the bronchoscopist according to experience and the situational need.^3,⁴

All FOBs have an illumination fiberoptic bundle and imaging fiberoptics or a camera. With the exception of the very few “ultrathin” bronchoscopes, there is also a channel for suction of secretions and blood, for the passage of topical medication and fluid for washing, and for the passage of various instruments for diagnostic retrieval of tissues or for therapeutic procedures (Table 75-1). The “average” diagnostic bronchoscope has an outer diameter of 5.0 to 5.5 mm and an operating channel of 2.0 to 2.2 mm. This caliber channel admits most cytology brushes, bronchial biopsy forceps, and transbronchial aspiration needles with sheathed outer diameters between 1.8 and 2.0 mm. Smaller bronchoscopes, in the range of 3.0 to 4.0 mm at the outer diameter and correspondingly smaller channels, are usually given a “P” designation (for pediatrics), but they can, of course, be used in the adult airways when narrowing is present because of benign strictures or malignant stenosis. Newer generations of “slim” video and fiberoptic bronchoscopes have a 2.0-mm operating channel with a 4.0-mm outer diameter. The one disadvantage of these bronchoscopes is the sacrifice of a smaller image area because of fewer optical bundles.

Table 75-1 Available Flexible Bronchoscopes, Dimensions, and Features

Larger “therapeutic” bronchoscopes (often designated with a “T” in the model number) can, of course, also be used for diagnostic purposes, but the larger outer diameter can cause greater discomfort and mucosal trauma in a conscious patient and can be harder to pass through an ET or tracheostomy tube, and thus can also impair gas exchange to a greater degree. Such therapeutic bronchoscopes have outer diameters between 6.0 and 6.3 mm, with operating channel lumens between 2.6 and 3.2 mm. Certain therapeutic instruments, including larger laser fibers, larger electrocautery forceps designed for gastrointestinal endoscopes, cryotherapy probes, and expandable balloons for bronchoplasty, require these larger diameters for their use through FOBs. Prototype bronchoscopes with a 9-mm outer diameter and a 5-mm operating channel have been made, the main application of which is to provide access for therapeutic instruments to airway segments that cannot normally be reached by rigid open-tube bronchoscopes and telescopes (Fig. 75-2).

Figure 75-2. Left to right, Range of fiberoptic bronchoscopes with outer/channel diameters of 4.9/2.0 mm and 6.0/2.8 mm, and a prototype therapeutic scope with diameters 9.0/5.0 mm. Note the insulated white ceramic plate, which is necessary for safe use of electrosurgery.

At the other extreme are the ultrathin bronchoscopes, with outer diameters smaller than 3 mm. The Olympus production models fiber BF-XP40 and video BF-XP160F (Olympus America, Center Valley, PA) have outer diameters of 2.8 mm and operating channels of 1.2 mm. Special instruments (e.g., reusable cytology brush and forceps) of the proper caliber are available for tissue sampling (Fig. 75-3). Handling of these ultrathin bronchoscopes is often more challenging because their very floppy tips make steering more difficult. Suction via the narrow channels is also much more limited. Nevertheless, with practice and the use of small amounts of saline to flush open the distal airways in guiding the bronchoscope forward, the ultrathin bronchoscopes can traverse 12 to 16 generations of airways and, under fluoroscopic or CT guidance, are seen to approach the periphery of the lungs to sample focal lesions.^3,⁴ The passage of a 2.8-mm instrument beyond the mid-teens division of the lobular bronchiole (measured at 0.7 mm in fixed tissue) calls into question some of the accepted measurements of the adult human airways. To permit the greater distance traversed, such ultrathin bronchoscopes usually have an operating length of 60 cm, 5 cm longer than the older bronchoscopes, although the current generation of videobronchoscopes are all built with a 60-cm working length.