While normally there is a dual blood supply from the bronchial and the pulmonary arteries, the bronchial circulation is not reestablished in standard lung transplantation. Previous anatomic studies have defined fairly consistent origins of the bronchial arteries from the intercostal arteries and descending thoracic aorta. The bronchial circulation provides an important blood supply to the major airways and supporting structures of the lungs. The bronchial arteries arise from the aorta or the intercostals and travel through the hila where small arterials penetrate the muscular layer of the airway and terminate in the bronchial mucosa. This termination is in the form of a submucosal plexus which eventually results in a collateral circulation between the pulmonary and bronchial circulations. Each proximal main stem bronchus receives its primary blood supply from the bronchial circulation although the pulmonary circulation can contribute via retrograde collaterals. While the much larger pulmonary circulation is reestablished at transplantation, the bronchial circulation is not. Therefore, bronchial viability and anastomotic healing are dependent upon retrograde blood flow from the pulmonary to bronchial circulation leaving the anastomosis and distal airway in jeopardy. Coronary collateral blood supply arises at atrial branches from the left and right coronaries. This collateral supplies the main carina as well as the proximal left and right main stem bronchi explaining why the more proximal airways do not seem to suffer the same ischemic risk.

The etiology of airway complications is likely multifactorial. Most theories attribute AC to ischemia, infection, or a combination of the two.

Every attempt is made to preserve undisturbed peribronchial tissue in an attempt to maintain the microvasculature. The benefits of particular anastomotic techniques are debated among surgeons, and there is no consensus practice. Wrapping the bronchial anastomosis with omentum or another vascularized pedicle has demonstrated reestablishment of collateral circulation at the level of the donor ­bronchus. Bronchial omentopexy appeared to be important in the early success reported by the Toronto group. The improvement in early neovascularity in addition to ­separating the bronchus from the mediastinum and pulmonary artery was an attempt to minimize the effect if a dehiscence were to occur. This procedure added complexity and morbidity primarily due to the addition of a laparotomy as well as a diaphragmatic defect. For these reasons, omentopexy is rarely practiced now. Additional anastomotic coverage with peribronchial tissue or other vascularized flaps have also been described although the data is weak as to their benefit. Anastomotic technique varies by institution and surgeon. There is some data to suggest that the risk of airway complication may be related to the type of anastomosis (see Fig. 45.2). The two most common types of anastomosis are the telescoping technique and the end-to-end anastomosis. Data exists which suggests that the telescoping technique is associated with more complications, particularly obstruction. Despite this, some surgeons still perform a telescoping anastomosis but agree that an exaggerated intussusception should be avoided whenever possible. An intussuscepted airway will predispose to an obstruction simply due to its anatomy. An obstruction seen in this airway will also be more difficult to dilate. In addition to this potential mechanical obstruction, any additional amount of sloughed necrotic tissue will lead to earlier obstructive symptoms. A significant intussusception may also allow for entrapment of the microorganisms between bronchi due to the microbiologic environment. For these reasons, most centers have adopted an end-to-end anastomotic technique as the procedure of choice unless donor-recipient bronchial size mismatch exists.

Airway complications also appear to be related to donor and recipient size mismatching. Differing diameters of donor and recipient bronchi have traditionally been treated with a telescoped anastomosis. This telescoping may lead to unwanted and potential deleterious stress at the suture line. Almost always, the size mismatch is a donor airway that is smaller than the recipient. A technique to manage this size mismatch is to perform an upper lobectomy on the recipient and anastomose the donor main stem to the bronchus intermedius on the right or the left lower lobe airway on the left.

Several other unavoidable risk factors which predispose a lung transplant anastomosis to complications exist. Although many of these risk factors may appear to be logical, most have not been demonstrated across institutions or in multi-institutional studies. Factors such as a male donor and a tall donor have been suggested. The anastomosis is seldom tension-free due to the wall stress created by positive pressure ventilation. This stress may predispose to injury and/or dehiscence. The length of donor time on mechanical ventilation has also been suggested with a time of 50–70 h increasing the probability of an airway complication. This may be related to an increased risk of infection while intubated. Airway anastomoses are sutured in the setting of a ­contaminated field. The necrosis often seen also provides a nidus for microbiologic growth. This milieu in conjunction with a suppressed immune system makes infection a major concern.

Although there have been considerable improvements in lung transplant survival, there is still a lag behind other solid organ transplants. Lung transplant patients are maintained at higher levels of immune suppression, but despite this, both acute and chronic rejection remain difficult problems to control, and chronic rejection manifested as bronchiolitis obliterans syndrome (BOS) occurs earlier with more dire consequences than other solid organ transplants. Immunosuppression is critical for the survival of an allograft; however, this may predispose to airway complications due to increased susceptibility to infection and diminished healing. Most immunosuppressive regimens consist of a calcineurin inhibitor (typically tacrolimus) in conjunction with an antilymphocyte (mycophenolate mofetil or azathioprine) and corticosteroid. Deserving special mention is sirolimus (rapamycin, Rapamune) which is a novel macrolide originally developed as an antifungal agent. It was later discovered to have potent immunosuppressive and antiproliferative properties which led to its use in renal and later lung transplantation. While the major drawback of calcineurin inhibitors is renal toxicity, this is seen at a much lower incidence with sirolimus. Sirolimus has been shown to be effective in controlling acute rejection and does not have overlapping toxicities with other immunosuppressants without the associated renal toxicities. This combination would make sirolimus appealing as an adjunctive medicine for the lung transplant population. However, in de novo recipients, sirolimus was shown to dramatically increase the rate of catastrophic airway complications. In particular, the rate of dehiscence was found to be unacceptably high in the early transplant period. The current recommendation is avoidance of sirolimus for at least 90 days after transplantation.

Comparison of airway complications after lung transplantation is made difficult by the lack of universally accepted classification system. However, there are several classification systems which address airway complications which are utilized. (Table 45.1)

Airway complications can be considered temporally, by etiology or descriptively. Several of the more common descriptive classifications include necrosis, dehiscence, stenosis/stricture, granulation tissue, infection, or fistula. Complications can be categorized as partial or full-thickness necrosis, obstruction, infection, or fistula. Airway necrosis, though not always considered a complication, may cause obstructive symptoms and is the early range of the spectrum including bronchial dehiscence. Obstruction may include airway stenosis from stricture, granulation tissue, or malacia. Included in obstruction is stricture at the anastomosis as well as a non-anastomotic narrowing in segmental or subsegmental airways.