Tracheobronchomalacia
Overview
Tracheobronchomalacia: A rare condition where delayed development of the cartilage that makes up the trachea results in excessive collapsibility of the trachea resulting in breathing difficulty
Symptoms
Expiratory wheezing Respiratory distress
Causes
The causes of TBM include the following: -Indwelling tracheotomy and endotracheal intubation with inflatable cuffs are considered to be common causes of acquired TBM, most likely resulting from pressure necrosis, decreased blood supply, infection, and friction of tubes on the airway mucosa.10,11 The malacic areas are focal and are usually seen at the site of the inflatable cuff, adjacent to the tracheostomy stoma, or at the point of impingement of the tip of the tracheostomy or endotracheal tube on the tracheal wall.10 -Long-term ventilation has been described in patients with Duchenne dystrophy who have had many years of positive pressure ventilation via tracheostomy.12 It is not clear whether the myopathic involvement of the tracheal muscularis also contributes to the weakness of the wall. Malacia has also been described in patients who have had long-term tracheostomies.13 -Closed chest trauma may cause unrecognized tracheal fractures, which can result in malacia. This is most likely the result of impairment in the blood supply.10 -Chronic irritation of the airways may weaken the airway wall. It can be the result of cigarette smoking or air pollution exposure, which are recognized risk factors for TBM.14 -Chronic inflammation can cause progressive atrophy and destruction of the tracheal or bronchial cartilages. This is most significant in patients with relapsing polychondritis, more than half of whom show involvement of the tracheobronchial tree.15,16 -Malignancy may cause focal malacia, such as that seen in tracheal or bronchial cancers or in extraluminal tumors that extend into and destroy the airway walls.1 -Mechanical anatomic factors, including postpneumonectomy syndrome17 and lung and heart-lung transplantation, can lead to malacia. In such cases, airway abnormalities are seen at or below the site of airway anastomoses.18 -Chronic infections, such as tuberculosis, may cause a progressive destruction or atrophy of cartilaginous rings.19 -Chronic compression of the tracheobronchial tree, as seen in substernal goiters and vascular anomalies, can lead to malacia.20,21
Diagnosis
n patients with TBM, dyspnea, cough, difficulty in clearing secretions, recurrent bronchitis, pneumonia, and respiratory failure have been reported.1,2,5,7,28 Cough is usually described as seal-like barking, which probably is caused by the vibration of the floppy membranous wall against the anterior airway wall during expiration.17 Wheezing is present in more than half of patients with TBM. Asthma-like exacerbations, characterized by wheezing and dyspnea, are less common and are usually refractory to corticosteroids and bronchodilators.28 Most patients have dyspnea on exertion, probably because during exercise, the airway collapse is worsened by increased intrathoracic pressures. Hemoptysis is rare in patients with TBM.29 Hypercapnic respiratory failure that requires mechanical ventilation or presents as an inability to wean off mechanical ventilation has been reported.30,31 A diagnosis of TBM should be considered in patients with obstructive ventilatory impairment who do not respond to conventional treatment with bronchodilators or inhaled corticosteroids. Any patient at risk for TBM should be evaluated if they have chronic respiratory symptoms. TBM should also be in the differential diagnosis of unexplained hypercapnic respiratory failure, especially in cases of failed extubation after successful weaning trials. TBM is a progressive disease in adults2,28 and in severe cases can be fatal; however, no reliable mortality data are available. Pulmonary function testing Few studies have rigorously reported results of pulmonary function testing in patients with malacia,4,5,32,33 and differences in disease definition account for considerable variability among those studies that do describe findings.5,33 The expiratory spirogram may reveal a "typical notch" on the volume-time curve,33,34 which might reflect a sudden diminution of flow at the beginning of expiration when the airway collapses. This spirogram is characterized by an initial phase in which a small volume is rapidly exhaled, followed by an upward deflection and then the continuation of exhalation.4,5 In patients with TBM, the flow-volume loop patterns on a spirogram may suggest compression of the central airways (Figure 2). The maximal flow is reached quickly after expiration of a small volume of air. Follow-ing the maximal flow, there is a significant decrease in flow, although only a small volume is exhaled. Then, the flow rate falls very little during the remainder of expiration; this phase is responsible for the long plateau of the flow-volume loop. Flow oscillations have also been described; they have a "saw-tooth" appearance, which is a reproducible sequence of alternating decelerations and accelerations of flow.32,34
Treatment
Therapy depends on the severity of symptoms, the degree and extent of airway collapse, and the underlying cause of TBM.1 Conservative management If permitted by the patient's clinical status, treatment of the underlying condition should be optimized before considering invasive therapies. Drug therapy should be used whenever possible before proceeding to more aggressive interventions. This is particularly the case for relapsing polychondritis, for which the main therapy consists of NSAIDs for mild disease and high-dose corticosteroids and various immunosuppressants for more severe forms. Corticosteroids are often effective in treating chondritis; they decrease the frequency and severity of recurrence. They do not, however, stop the late loss of cartilaginous support and, in fact, may not influence survival.1 Noninvasive positive pressure ventilation can be used to maintain airway patency, facilitate secretion drainage, and improve expiratory flow. The addition of nasal continuous positive airway pressure (CPAP) improves spirometry values, sputum production, atelectasis, and exercise tolerance.42,52 Although large controlled studies are needed to confirm these findings, it seems that nocturnal and intermittent daytime nasal CPAP benefits patients with TBM and can be used as adjunctive therapy. Although various levels of CPAP were applied, 10 cm H2O of CPAP appeared optimal for all patients, based on observed plateaus in expiratory airflow, near-normalization of airway collapse during active expiration, and degree of patient tolerance and comfort. Minimally invasive surgery Airway stents can successfully maintain airway patency and result in improved pulmonary function (Figure 4).1 If symptoms do not improve, stent removal is probably required to avoid stent-related complications, including migration, obstruction by mucus or granulation tissue, infection, fracture, and airway perforation.1 Close follow-up is warranted and any recurrence of symptoms of TBM should prompt immediate bronchoscopy.53 Open surgery Tracheostomy may stent the malacic airway and provides invasive ventilatory support when necessary.1 Tracheostomy, however, can be complicated by secondary tracheomalacia and stenosis at the stoma site54 and should probably not be considered as a first-line treatment in elective cases. Tracheal resection has been proposed for focal tracheomalacia; it has been shown to have good outcome and low mortality in experienced centers.55 Airway splinting via tracheoplasty has been used to consolidate and reshape the airway wall. This technique allows reinforcement of the membranous portion of the trachea in crescent-type malacia56 with outcomes that appear favorable in uncontrolled studies.57 Other techniques that have been reported include tying the posterior wall of the trachea with bone chips, fascia grafts, or plastic prostheses; performing autologous coastal cartilage grafts to support the tracheal wall; suturing the trachea to dura mater grafts1; and implanting biocompatible ceramic rings.58 The authors are affiliated with the division of pulmonary and critical care medicine at the University of California School of Medicine in Irvine. Dr Murgu is a clinical instructor, and Dr Colt is professor of medicine and director of clinical programs.