These mid-century experiences in tracheal reconstruction, chiefly in the upper trachea, and most often of limited extent, made it clear that the basic techniques of tracheal anastomosis could achieve sound healing. The "2 cm rule," which had served to inhibit advances in tracheal surgery, was now challenged by experimental studies reinvestigating the extent of trachea that could be removed, and approximation achieved by anatomic tracheal mobilization, without use of prosthetic replacement. Clinical experiences, especially with intrathoracic and carinal lesions, contributed to widening the possibilities for more extended resection.
Ferguson and colleagues determined the extensibility of human trachea from cadavers to be 35% at 29 years and 17% at 76 years, with the most stretch reached with 200 g of tension.43 In living dogs, the majority of resectable length was obtained at 450 g of tension at the anastomosis, which is about 30 to 35% of the tracheal length. Michelson and colleagues, in an effort to increase the length of resectable trachea, freed the right main bronchus in dogs by incising the right pulmonary ligament and resecting the left main bronchus at the carina, and then reanastomosing it to the bronchus intermedius.78 This permitted resection of twelve rings in the dog. They found that the human trachea could be stretched 4 to 6 cm by mobilization, and that an added 2.5 to 5 cm could be obtained by the maneuver described in dogs. Tracheal elongation in fresh human cadavers, with the same dissection and 450 g of upward pull, allowed 2.5 to 3 cm elevation after division of the pulmonary ligament, and 5 to 6 cm after freeing the left main bronchus in four cadaver subjects under 50 years of age. Respectively, 1 to 1.5 and 2 to 3 cm were measured in four subjects at 50 to 75 years of age. Cantrell and Folse sought to determine the limits of feasibility of primary anastomosis in repair of circumferential defects.61 In resection of 20 to 58% of dog trachea, the suture line tension ranged from 400 to 2,750 g. The tension required for anastomosis varied markedly between flexed and extended neck positions. Disruption of anastomosis occurred between 1,700 and 3,100 g, at resection lengths of 46 to 63% of the trachea. However, they noted in human trachea obtained at autopsy that resection of more than 2 cm over the age of 80 produced unacceptable anasto-motic tension, based on experimentally derived standards.
In 1959, Harris showed radiologically that neck extension elongated the trachea by 2.6 cm.79 Som and Klein extended the length of human cadaver trachea by only 1.6 cm by circumferential incision of the inter-cartilaginous annular ligaments.80
Grillo and colleagues reported in 1964, from autopsy studies in man, that over half of the adult trachea could be resected and continuity reestablished by full mobilization of limiting structures (Figure 2).81 Steps in mobilization were 1) right hilar dissection and division of right pulmonary ligament, 2) division of left main bronchus, and 3) freeing pulmonary vessels from the pericardium. With the subject's neck in neutral position, these steps permitted tracheal excisions averaging 3 cm (3 to 8 rings), 2.7 cm (3 to 12 rings), and 0.9 cm (0.5 to 3 rings), for a total of 6.4 cm (11 to 18 rings). Anastomotic tension rose exponentially with resection of successive 1 cm segments, from 25 g at 1 cm to 675 g at 7 cm. Age did not prove to be seriously limiting. This was considerably below the biologically dangerous limit of 1,700 g determined by Cantrell and Folse.61 Division of the left main bronchus allowed the advancement of the distal tracheal stump and right main bronchus.
In addition, if an even more extended resection was to be necessary, division of the cervical trachea two to three rings below the cricoid allowed this segment of cervical trachea to be devolved into the mediastinum with intact lateral vascular supply.81 This maneuver proposed to allow reconstruction of the intrathoracic trachea by simple anastomosis, while permitting later staged reconstruction of the cervical trachea, which would be more safely possible. Because of the complexity of this last approach, division and reimplantation of the left main bronchus was later applied clinically, only in the case of carinal reconstruction, and then, rarely.
Stimulated by Grillo's clinical experiences with cervical tracheal resection for postintubation stenosis, Mulliken and Grillo reported in 1968 an investigation of the amount of trachea that might be resected by cervical and mediastinal mobilization and still permit anastomosis, leaving the pleural cavity intact.82 Pretracheal mobilization was done down to the carina, with division of the thyroid isthmus, in cadavers. With the neck in 15 to 35 degrees of flexion, 1,000 to 1,200 g of tension applied to the divided tracheal ends permitted an average resection and reapproximation of 4.5 cm (7.2 rings). Right hilar mobilization with the pleura open allowed an increment of resection of 1.4 cm (2.5 rings), giving a total of 5.9 cm. The average tracheal length was 11 cm. Cervical flexion permitted a gain of 1.3 cm (2.5 rings) over the neutral position. Thus, cervical flexion and pretracheal mobilization alone appeared to allow significant cervical or cer-vicomediastinal resection and anastomosis, especially important for the postintubation lesions, which were increasing in frequency, and that often occurred in patients who could not tolerate thoracotomy.
Appreciation of the possible degree of tracheal mobilization, based upon anatomic principles(ie, pre-tracheal mobilization, cervical flexion, hilar dissection, including intrapericardial freeing, and mobility of detached main bronchi), made possible a systematic and aggressive approach to tracheal resection and reconstruction not previously conceived. The episodic ad hoc approach, which produced single case reports, at times almost expressing a surgeon's surprise at what he was able to accomplish, yielded to more confident and planned approaches. Using such principles, significant series of resections and reconstructions of cervical and thoracic tracheae for stenosis and tumor were reported by Grillo, Deverall, Perelman, Naef, Couraud, Pearson, Dor, Levasseur, and Harley and their colleagues.83-93
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