Surgical Anatomy of the Trachea and Techniques of Resection and Reconstruction
Moishe Liberman
Douglas J. Mathisen
This chapter is a revision, adaptation, and update on the original chapter written by Hermes C. Grillo, MD, who passed away on October 14, 2006, at the age of 83. Dr. Grillo was and will always be the father of modern tracheal surgery and is responsible for a large part of what is known about the anatomy of the trachea and for many of the procedures currently being performed on patients with diseases of the trachea and bronchi.
Anatomy
Functionally, the trachea serves principally as a conduit for ventilation. Viewed in this way, it would seem to be an ideal structure for replacement or reconstruction when involved by surgical disease. Anatomically, however, it presents several unique features that partially account for the difficulty in its surgical management. These features are its unpaired nature, unique structural rigidity, short length, relative lack of longitudinal elasticity, proximity to major cardiovascular structures, and segmental blood supply.
The adult human trachea averages 11.8 cm in length (range, 10 to 13 cm) from the infracricoid level to the top of the carinal spur. Typically, 18 to 22 cartilaginous rings occur within this length, approximately two rings per centimeter. Occasionally, rings are incomplete or bifid. In an adult male, the internal diameter of the trachea measures about 2.3 cm laterally and 1.8 cm anteroposteriorly. These measurements vary roughly in proportion to the size of the individual and are usually smaller in women. The cross-sectional shape of the adult trachea is nearly elliptic. In infants and children, the trachea is more circular. The configuration may change with disease. The lower two-thirds may be flattened in tracheomalacia or rigidly narrowed from side to side to produce a saber-sheath trachea.
The surgeon usually visualizes the trachea as he or she learned to see it in the thyroidectomy position, with the neck extended, as a structure that is one-half cervical and one-half thoracic. However, the trachea becomes almost entirely mediastinal when the neck is flexed because the cricoid cartilage drops to the level of the thoracic inlet.36 This may be the permanent position in aged people secondary to cervical kyphosis. These simple observations have contributed to the development of surgical reconstructive techniques that obviate the requirement for prostheses.
When viewed laterally in the upright individual, the trachea courses backward and downward at an angle from a nearly subcutaneous position at the infracricoid level to rest against the esophagus and vertebral column at the carina. The larynx and the origin of the esophagus are intimately related anatomically at the cricopharyngeal level. Below this point, the posterior membranous wall of the trachea maintains a close spatial relationship to the esophagus. A distinct, easily separable plane is present below the cricoid level, but a common blood supply is shared. Anteriorly, the thyroid isthmus passes over the trachea in the region of the second tracheal ring. The lateral lobes of the thyroid are closely applied to the trachea, and a common blood supply is obtained from the branches of the inferior thyroid artery. Lying in the groove between trachea and esophagus are the recurrent laryngeal nerves, coursing from beneath the arch of the aorta on the left side and therefore having a longer course in proximity to the trachea than on the right side, where the nerve loops around the subclavian artery and then approaches the groove. A nonrecurrent nerve is rarely present on the right in conjunction with an anomalous subclavian artery. These nerves enter the larynx between the cricoid and thyroid cartilages just anterior to the inferior cornu of the thyroid cartilage.
The anterior pretracheal plane may be easily developed though a cervical approach. Fibrofatty tissue, lymph nodes, and fine branches of the anterior jugular vein are present in front of this plane. The innominate vein lies anteriorly, away from the trachea. The innominate artery, however, crosses over the midtrachea obliquely from its point of origin from the aortic arch to the right side of the neck. In children, the innominate artery is higher and is encountered in the lower part of the neck. In some adults, the artery is unusually high and crosses the trachea at the base of the neck when slight cervical extension is present. Occasionally, a tiny branch of this artery may be encountered in the segment of the artery that crosses the trachea. At the level of the carina, the left main bronchus passes beneath the
aortic arch and the right beneath the azygos vein. The pulmonary artery lies just in front of the carina. On either side of the trachea lies fibrofatty tissue containing lymph node chains and a large packet of nodes lies just beneath the carina (see Chapter 6).
aortic arch and the right beneath the azygos vein. The pulmonary artery lies just in front of the carina. On either side of the trachea lies fibrofatty tissue containing lymph node chains and a large packet of nodes lies just beneath the carina (see Chapter 6).
 Figure 79-1. Blood supply of the trachea. A: Right anterior view. B: Left anterior view. The right side varies in some respects. (From Salassa JR, Pearson BW, Payne WS. Gross and microscopical blood supply of the trachea. Ann Thorac Surg 1977;24:100. With permission.) |
The course of the trachea from the anterior cervical position to the posterior mediastinal position with close relationships to major vascular structures makes access to the entire trachea through a single incision difficult. Grillo12 emphasized that these anatomic relationships demand precise definition of the extent and nature of tracheal lesions when surgical procedures are being planned.
The cartilaginous rings give the human trachea its lateral rigidity. They extend about two-thirds of the circumference. The posterior wall is membranous. The trachea is lined with respiratory mucosa, which is tightly applied to the inner surface of the cartilages grossly. The normal epithelium is columnar and ciliated. The cilia clear particulate matter and secretions. Mucous glands are liberally present. In chronic smokers and in persons with other chronic irritation, squamous metaplasia frequently occurs; in extreme instances, few ciliated cells remain. Such individuals must clear secretions by coughing vigorously. This observation, plus the demonstrated feasibility of cutaneous reconstructions and occasional successes with prosthetic interpositions, makes it clear that ciliated epithelium, although highly desirable, is not essential for tracheal reconstruction. Between the cartilaginous rings and in the membranous wall, the submucosa is fibromuscular.
Considerable contraction of the muscular membranous wall can occur with coughing and spasm, the tips of the cartilages being drawn inward. Such transient narrowing of the airway may be observed fluoroscopically and during bronchoscopy in normal individuals. Some longitudinal flexibility exists; a degree of elasticity is present that appears to be greater in youth and to decrease with age. Calcification of the rings is seen most often with advancing age, although to a lesser degree than in the cricoid cartilage. Local trauma or operation may also lead to calcification. The normal trachea slides easily in its layer of fibrofatty areolar tissue from neck to mediastinum.
The blood supply of the human trachea is segmental, largely shared with the esophagus and derived principally from multiple branches of the inferior thyroid artery above and the bronchial arteries below. The arteries approach laterally, and fine branches pass anteriorly to the trachea and posteriorly to the esophagus. Miura and Grillo34 demonstrated that the inferior thyroid artery nourishes the upper trachea, usually through a pattern of three principal branches with fine subdivisions and extremely fine collateral vessels but with many variations, as noted by Salassa and colleagues.39 The bronchial vessels nourish the lower trachea, carina, and mainstem bronchi. Sometimes the internal mammary artery contributes (Fig. 79-1). Excessive circumferential dissection with division of the lateral pedicles during an operative procedure can easily devascularize the trachea.
Methods of Reconstruction of the Trachea Methods of Reconstruction of the Trachea
The surgical approach to the trachea developed at a slower pace than that to other areas of thoracic surgery owing to the rarity of tracheal tumors, the anatomic complexities of reconstruction, and the biologic incompatibilities that met efforts at prosthetic reconstruction.21 Earlier hesitations because of problems of physiologic management during reconstruction proved to be less formidable. The growth in frequency of postintubation benign lesions, due to the success of modern respiratory therapy, increased the urgency of developmental work.
The concept of direct end-to-end anastomosis of trachea to trachea was generally accepted as the ideal method of tracheal repair after reconstruction. It was long believed, however, as stated by Belsey,2 that no more than 2 cm (about four tracheal rings) could be removed and anastomosis consistently made. As
a result, lateral resection was done when possible, with attempts made to patch the defect in various ways, using fascia, skin, pericardium, other tissues, and foreign materials. When such a technique was applied to malignant neoplasms, inadequate removal of tumor resulted, with early recurrence. Such patches also failed to heal. Partial cicatrization was an additional factor. Attention was directed early to the development of an artificial trachea.
a result, lateral resection was done when possible, with attempts made to patch the defect in various ways, using fascia, skin, pericardium, other tissues, and foreign materials. When such a technique was applied to malignant neoplasms, inadequate removal of tumor resulted, with early recurrence. Such patches also failed to heal. Partial cicatrization was an additional factor. Attention was directed early to the development of an artificial trachea.
Anatomic Mobilization
Perhaps most crucial to the evolution of mobilization techniques for tracheal reconstruction was recognition that the cervical trachea, as seen in the hyperextended surgical thyroid position, may be delivered into the mediastinum by cervical flexion. A few reports of clinical resections >2 cm appeared, but few systematic studies of the anatomic potential are recorded. Michelson and associates32 noted that careful mobilization of the entire trachea in eight cadavers allowed for anastomosis with 1 pound of tension, after resection of 4 to 6 cm, with an additional 2.5 to 5.0 cm obtained by division of the left main bronchus.
Detailed anatomic studies in cadavers attempted to answer the surgical questions of how much trachea could be resected with primary anastomosis when the trachea was reached in progressive fashion from either a cervical or a transthoracic approach, depending on the location of the lesion. Mulliken and Grillo36 mobilized the trachea through a cervicomediastinal approach, carefully preserving the lateral tissue bearing its blood supply. Using a standard tension of 1,000 to 1,200 g for approximation, it was possible, with the neck in 15 to 35 degrees of flexion, to resect an average length of 4.5 cm (about seven rings) and to increase this by 1.4 cm by entering the pleural space and mobilizing the right hilum (Fig. 79-2A). With greater degrees of cervical flexion, even longer resections are possible. Suprahyoid laryngeal release, described by Montgomery,35 adds 1.0 to 1.5 cm of length while minimizing the difficulties in swallowing that attended earlier techniques for release. Alternating lateral division of the intercartilaginous ligaments of the trachea to obtain extension has been proposed experimentally but not applied clinically to any extent. This technique has the disadvantages of probable interference with tracheal blood supply and the need for extensive tracheal exposure to obtain a rather limited extension of length.
In approaching the lower half of the trachea, Grillo et al.10 accomplished progressive mobilization by first freeing the hilum of the right lung and dividing the inferior pulmonary ligament; second, freeing the pulmonary vessels from their pericardial attachments; and third, transplanting the left main bronchus, which is held in place by the arch of the aorta, to the bronchus intermedius. In these earlier studies, the neck was held in the neutral position. At tensions under 1,000 g, the first maneuver allowed for resection of 3 cm and the second for an additional 0.9 cm; the radical measure of bronchial implantation permitted an additional 2.7 cm (Fig. 79-2B). It has since become clear that cervical flexion, combined with hilar and pericardial mobilization plus division of the pulmonary ligament, allows lengths of 5 to 6 cm to be removed by the transthoracic approach. These figures represent only guidelines. The length of trachea that may be resected safely in an individual varies widely with age, posture, body habitus, extent of disease, and prior tracheal surgery. Bronchial implantation has been reserved for carinal resection or similar complex maneuvers to avoid adding another unnecessary risk to operation. Reimplantation of the left main bronchus into the bronchus intermedius was first used clinically by Barclay and associates.1
 Figure 79-2. The amounts of trachea that can be removed and yet permit primary anastomosis. A: Cervicomediastinal mobilization permitted removal of 4.5 cm under 1,000-g tension with cervical flexion. Intrathoracic dissection permitted removal of an additional 1.4 cm. B: Transthoracic hilar dissection and division of the pulmonary ligament, with the cervical spine in the neutral position, permitted removal of 3 cm, intrapericardial dissection an additional 0.9 cm, and division of the left main bronchus with reimplantation in the bronchus intermedius an additional 2.7 cm. The use of cervical flexion has demonstrated that the area designated I may be significantly >3 cm. (From Grillo HC. Surgical approaches to the trachea. Surg Gynecol Obstet 1969;129:347. With permission.) |
The limits of safety with varying anastomotic tensions have not been established in humans. Cantrell and Folse4 found that, in dogs, tensions below 1,700 g permitted safety from disruption after anastomosis. In anatomic studies in the cadaver, Grillo found that an average tension of only 675 g was required for approximation (maximum, 1,000 g) after a 7-cm resection. Such clinical measurements show tensions of about 600 g in resections of 4 to 5 cm in length. Although about one-half of the adult trachea is safely resectable in most adults, with the caution expressed, Wright43 observed clinically that the more fragile juvenile trachea is at risk if resection exceeds about one-third.
Anatomic and clinical observations have demonstrated that great attention must be paid to the lateral blood supply during tracheal mobilization. This fine segmental supply cannot be disrupted safely, particularly for anastomosis of a long distal segment to a short proximal segment; the distal segment must not be freed circumferentially.
Another peculiarity of tracheal reconstruction depends on the relative rigidity of the anterolateral walls. Transverse wedging of the anterior wall of the trachea may buckle the posterior wall into a partially obstructing valve. Circumferential resection, which may, however, be beveled, is most often preferable.
Surgery of the Trachea
Anesthesia
The airway must be under full control at all times during reconstructive surgery of the trachea, so that hypoxia does not occur. The patient should preferably breathe spontaneously during the operation and always at its conclusion so that ventilatory support is not necessary postoperatively. Cardiopulmonary bypass has been used for tracheal surgery, but it is not necessary for relatively simple resection and, as noted by Geffin and colleagues,8 presents real hazards for more complex procedures requiring extensive manipulation of the lung. Procedures are explained carefully to the patients before the operation.
Induction is carried out slowly and gently, especially in a patient with a highly obstructed trachea. If a benign stenosis presents an airway diameter of <5 mm, dilatation is performed, and an endotracheal tube is passed beyond the lesion to prevent arrhythmia caused by CO2 buildup during the early stages of operation. Occasionally, a nearly obstructing tumor has required prompt bronchoscopy with a ventilating bronchoscope shortly after induction, with subsequent intubation. An obstructing tumor may be cored out with the rigid bronchoscope aided by biopsy forceps. Frequent monitoring of blood gases and electrocardiography are essential. Bronchoscopic examination should be done by the surgeon and observed by the anesthetist, who must deal with this airway until surgical access distal to the lesion has been obtained. If tracheostomy is already present, induction is simplified. Initial dissection is always done carefully to avoid increasing the degree of obstruction by roughness or pressure.
In patients with critical airway stenoses, an inhalational induction technique should be employed in order to preserve spontaneous ventilation. A slow inhalational induction may be required if there is a high degree of obstruction. This technique is preferable to paralysis of respiration, which may necessitate the urgent establishment of an airway. In patients with less critical airway stenoses, total intravenous anesthesia (TIVA) techniques (the use of an IV agent or agents exclusively to provide a complete anesthetic) can be used. This allows for prompt reversal and spontaneous breathing following resection and reconstruction. The goal should be extubation of all patients undergoing tracheal resection at the end of the procedure. Particularly where the trachea has been greatly shortened, it is desirable not to have even a low-pressure cuff lying in contact with the anastomosis for any length of time.
The area below the obstruction is isolated first, so that a transection of the trachea can be performed at any point and an airway can be introduced across the operative field should the degree of obstruction increase. Sterile anesthesia tubing, connectors, and endotracheal tubes are available in the operative field. At the time of tracheal division, the orotracheal tube is pulled back or removed and a sterile, cuffed, flexible, armored endotracheal tube is inserted into the distal airway across the operative field. Sterile connecting tubing is passed to the anesthesiologist to allow ventilation of the patient. This armored tube is removed whenever necessary for suctioning or placement of sutures. Toward the completion of the operation, the original endotracheal tube is advanced into the distal airway and the anastomotic sutures are tied.
It is usually not necessary to make distal incisions in the tracheobronchial tree for insertion of ventilatory catheters. If transthoracic resection is performed close to the carina, the endotracheal tube is passed into the left main bronchus and that lung alone is ventilated; if the PO2 decreases toward unsatisfactory levels, a previously isolated right main pulmonary artery is temporarily clamped to eliminate the shunt through the right lung. This is rarely required. Slow increase in shunting may occur during prolonged operation because of low tidal volume ventilation, increasing atelectasis, and aspiration of secretions; it must be guarded against.42 High-frequency ventilation is a useful adjunct, especially in complex carinal reconstruction.7
Surgical Approaches
Lesions in the upper half of the trachea that are known to be benign are best approached cervically (Fig. 79-3A). If a malignant lesion is present, one must be prepared for a cervicomediastinal and, possibly, a transthoracic approach. Placement of the cervical incision depends on the pathologic state, the presence of existing stomas, and the possible need for sternotomy. If a postoperative temporary tracheostomy stoma may be required after a difficult laryngotracheal anastomosis, the incision must be planned so that a stoma can be made away from the incision. If the initial dissection through the neck indicates need for further exposure, the upper sternum is split to a point just beyond
the angle of Louis; horizontal division of the sternum into an intercostal space is not necessary. Because the great vessels present anteriorly, division of more than the upper sternum is not helpful; division simply allows room to maneuver in managing the more distal trachea (Fig. 79-4B). Innominate vein division also adds nothing to the exposure.
the angle of Louis; horizontal division of the sternum into an intercostal space is not necessary. Because the great vessels present anteriorly, division of more than the upper sternum is not helpful; division simply allows room to maneuver in managing the more distal trachea (Fig. 79-4B). Innominate vein division also adds nothing to the exposure.
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