CPAP Treatment for Moderate Diffuse Excessive Dynamic Airway Collapse Caused by Mounier-Kuhn Syndrome

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Chapter 13 CPAP Treatment for Moderate Diffuse Excessive Dynamic Airway Collapse Caused by Mounier-Kuhn Syndrome

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This chapter emphasizes the following elements of the Four Box Approach: indications, contraindications, and expected results; anesthesia and other perioperative care; and techniques and instrumentation.

Case Description

The patient was a 70-year-old man with “seal barking” cough for longer than a year. His cough was associated with congestion and was worse at night and in the supine position. He had dyspnea on exertion (World Health Organization [WHO] class II). His past medical history was significant for asthma and frequent hospitalizations for pneumonia and “bronchitis.” At the time of our evaluation, his medications included fluticasone/salmeterol 250/50 mg twice daily, tiotropium one inhalation daily, prednisone 10 mg/day, mometasone nasal spray, Mucinex, loratadine, and inhaled tobramycin for recurrent lower respiratory tract Pseudomonas aeruginosa infection. In addition, he was using omeprazole 20 mg daily for gastroesophageal reflux disease (GERD) and albuterol 2.5 mg nebulization 3 times daily, followed by application of high-frequency chest oscillation (i.e., percussion vest). He was not a smoker and had no occupational exposure to fumes and toxins. On examination, wheezing over the trachea and bilateral rhonchi could be heard early during expiration. His oxygen saturation was 92% on 4 L/min of oxygen. Pulmonary function testing (PFT) revealed the following: forced expiratory volume in 1 second (FEV1) 1.93 L (51% predicted), which increased to 2.26 L (60% predicted), resulting in 17% improvement after bronchodilators; and forced vital capacity (FVC) 2.62 L (52% predicted) increased to 3.19 L (63% predicted)—a 22% improvement after bronchodilators. Total lung capacity (TLC) was 98% predicted, residual volume (RV) 171% predicted, and diffusing capacity of the lung for carbon monoxide (DLCO) 89% predicted. A paired inspiratory-expiratory dynamic computed tomography (CT) scan of the chest showed tracheobronchomegaly, expiratory bulging of the posterior membrane inside the airway lumen, narrowing the cross-sectional area of the trachea and mainstem bronchi by 67%, and bronchiectasis (Figure 13-1). A review of his old records revealed that several sputum and bronchioloalveolar lavage (BAL) cultures showed multiple bacteria, including Stenotrophomonas, Nocardia, Escherichia coli, Pseudomonas, and Aspergillus.

Case Resolution

Initial Evaluations

Physical Examination, Complementary Tests, and Functional Status Assessment

This patient’s PFTs showed moderate obstructive ventilatory impairment responsive to bronchodilators, a normal DLCO, and evidence of air trapping. These findings were consistent with his diagnosis of asthma. The CT scan, however, showed tracheobronchomegaly, moderate EDAC on expiratory images, bronchiectasis, bronchial thickening, and bronchiolitis in the lower lobes (see Figure 13-1). During the initial evaluation of a patient with bronchiectasis, the presumed cause of this patient’s recurrent episodes of bronchitis and pneumonia, the clinician must select diagnostic studies to determine the cause of the disorder. If bronchiectasis is truly focal (i.e., confined to one lobe), then it is highly unlikely that inherited or systemic causes are responsible, and investigations can be tailored appropriately,1 for example, bronchoscopy might be performed to identify possible obstruction by foreign body, tumor, or stricture (Figure 13-2).

In a patient with bilateral bronchiectasis, such as that noted in our patient, a battery of immunologic and genetic tests can be tailored on the basis of clinical suspicions.1 Our patient had no evidence of autoimmune disease, immunodeficiency, or genetic disorders such as alpha 1-antitrypsin deficiency or cystic fibrosis: The autoantibody screen that comprised antinuclear antibodies (ANAs), antineutrophil cytoplasmic antibodies (ANCAs), anti-SSA, anti-SSB, and rheumatoid factor, along with cystic fibrosis (CF) testing for 97 mutations, was negative; the alpha 1-antitrypsin level and immunoglobulin (Ig)G, IgM, IgA, and IgE were normal; and the erythrocyte sedimentation rate (ESR) was slightly elevated at 25 (normal <20). Because chronic aspiration is another cause of bilateral bronchiectasis, an esophagogram and a hypopharyngogram were performed, revealing no evidence of aspiration or obstruction. However, high-grade reflux, which in fact can be seen in almost a fourth of patients with bronchiectasis, is usually asymptomatic. One study showed that only 27% of patients with bronchiectasis and coexisting GERD have typical reflux symptoms such as heartburn, regurgitation, or dyspepsia.2

Today, chest high-resolution computed tomography (HRCT) scans are performed in almost anyone suspected of having bronchiectasis. A classic finding of bronchiectasis is the “signet ring” sign (this was present in our patient), characterized by a diameter of the bronchus greater than the adjacent artery (broncho-arterial ratio >1)* (see Figure 13-1). Bronchial wall thickening, bronchi filled with mucus, and mosaic perfusion (air trapping on expiration) are indirect HRCT signs that assist in diagnosis (Figure 13-3; see also Figure 13-1). HRCT also narrows the differential diagnosis by revealing specific disease processes such as situs inversus in Kartagener syndrome (see Figure 13-3), or by revealing a specific distribution of the abnormalities. For instance, in allergic bronchopulmonary aspergillosis (ABPA),* the distribution of bronchiectasis is usually central (see Figure 13-3), but in tuberculosis, it is usually unilateral and upper lobe predominant. In our patient, the distribution was in the lower lobes, suggesting impaired mucociliary mechanisms or postinfectious causes. In addition, HRCT, when performed with a dynamic protocol, can detect and quantify the degree of central airway collapse.3 Very high resolution images and three-dimensional (3D) reconstruction using 320-slice CT have been reported for diagnosis of EDAC.4

The patient’s “seal barking” cough, nocturnal congestion in the supine position, and wheezing were suggestive of expiratory central airway collapse. The paired inspiratory-expiratory dynamic CT showed tracheobronchomegaly, mild tracheal collapse (67%), and moderate collapse in the mainstem bronchi, with near complete closure of the lumen during exhalation (90%)* (see Figure 13-1). Tracheobronchomegaly is usually secondary to bilateral upper lobe fibrosis as a sequel of pulmonary fibrosis, tuberculosis, cystic fibrosis, or sarcoidosis (Figure 13-4), but our patient had other parenchymal/interstitial lung findings on HRCT.

In the absence of alternative explanations, we believed that our patient had primary tracheobronchomegaly in association with bronchiectasis—findings known as Mounier-Kuhn syndrome. This syndrome is characterized by atrophy or absence of elastic fibers and smooth muscle cells. These structural alterations may lead to collapse of the airway during exhalation, making expectoration by cough inefficient. Although considered to be a congenital condition, 50% of patients have no symptoms until the third decade of life, when frequent lower respiratory tract infections and sputum production become manifest, probably as a result of bronchiectasis.5

Procedural Strategies

Indications

Flexible bronchoscopy was indicated in this patient for several reasons: (1) to obtain specimens for microbiologic assessment of the chronically infected lower airways; (2) to perform dynamic bronchoscopy to diagnose and determine the severity of EDAC suggested by the dynamic CT scan; and (3) to apply CPAP assistance during bronchoscopy to determine precise CPAP pressures that maintain airway patency and prevent excessive collapse. These three aspects of the procedure were discussed with the patient and his spouse, who had accompanied him to the consultation.

1. Bronchoscopic diagnosis of infection: Infections play an important role in exacerbation of bronchiectasis and baseline symptoms. Our patient’s main reason for chronic infections and exacerbations was his anatomic airway abnormality. Excessive collapse of the trachea and mainstem bronchi leads to inability to raise secretions, infections, damage to the bronchial walls, and progressive airway dilation (bronchiectasis). This further reduces one’s ability to clear secretions from the distal airways, setting up a repetitive cycle of purulent drainage and tissue damage.9 Studies using techniques that have avoided contamination by upper airway flora (such as bronchoscopic protected brush specimens and BAL) show that more than 50% of patients with bronchiectasis have potentially pathogenic bacteria in their lower airways. Although the presence of pathogenic bacteria in the lower airways in these patients has often been termed colonization, the spectrum of pathogenic bacteria isolated in patients at baseline and during exacerbations is remarkably similar.* Furthermore, improvement in baseline symptoms after long-term antibiotics suggests that bacteria may be causing inflammation.1012 Some pathogens have a definite role in long-term prognosis. Relevant to this patient, the isolation of Pseudomonas aeruginosa correlates with severe clinical disease in bronchiectasis, occurs later in the course of disease,13 and is associated with a decline in lung function as measured by FEV1 (50 mL/yr).14

2. One indication for dynamic bronchoscopy (aka functional bronchoscopy) is the evaluation of EDAC. This technique allows for real-time observations of changes in the airways in response to various maneuvers. It is performed using flexible bronchoscopy with minimal or moderate (conscious) sedation so that the patient can cooperate and obey commands during the procedure.15 With the flexible bronchoscope at the midline, the patient is asked to inhale and exhale deeply, hyperflex and hyperextend the neck, and cough. These maneuvers are done while the patient is placed in upright, supine, and lateral decubitus positions (Figure 13-5).

3. CPAP (or BiPAP) assistance during flexible bronchoscopy can be used to confirm the possible effectiveness of conservative management in symptomatic patients with expiratory central airway collapse (EDAC or malacia), as well as to prevent respiratory distress and intubation in high-risk patients requiring flexible bronchoscopy.16,17 Bronchoscopy allows removal of mucus plugs and improves ventilation and oxygen exchange, but by occupying 10% to 15% of the normal tracheal lumen, the bronchoscope can decrease PaO2 (partial pressure of oxygen in arterial blood) by 10 to 20 mm Hg, which may contribute to respiratory complications and cardiac arrhythmias. Hypoxemia is worsened when local anesthetics or saline solution is instilled into the lower airways. The American Thoracic Society recommends avoiding flexible bronchoscopy and lavage in patients with hypoxemia that cannot be corrected to at least a PaO2 of 75 mm Hg or an SaO2 (saturated oxygen level in hemoglobin) greater than 90%.18,19 In patients with severe obstructive ventilatory impairment, bronchoscopy can lead to air trapping because functional residual capacity (FRC) increases when the scope is inserted nasally; and in children and in patients with OSA or obesity hypoventilation syndrome (OHS) who already have awake hypercapnia, bronchoscopy can exacerbate hypoxemia and hypercapnia because of sedation-related increased collapsibility of the central and upper airways. In these settings, bronchoscopy can be performed with CPAP or BiPAP assistance, potentially sparing patients the discomfort and risks of refractory hypoxemia, intubation, and mechanical ventilation.20,21 However, CPAP can thwart an accurate evaluation of dynamic airway obstruction by preventing airway collapse. For this reason, dynamic airway lesions within extrathoracic and intrathoracic airways (e.g., laryngomalacia, tracheobronchomalacia [TBM], EDAC) should be bronchoscopically visualized with and without CPAP to assess collapsibility.22

Expected Results

CPAP can be used in patients with EDAC or TBM to ameliorate airway collapse. The exact CPAP settings that maintain airway patency in expiratory central airway collapse of various degrees of severity have not been systematically studied. If an evaluation of central airway collapse is performed, digital imaging documentation is obtained in upright and supine positions both on and off CPAP so the degree of airway narrowing and the response to positive pressure can be evaluated. The pressure requirements are individualized and determined during CPAP-assisted bronchoscopy, or, alternatively, with CPAP-assisted CT scanning.4 A recent case study reported that a pressure of 10 cm H2O abolished a patient’s symptoms and ameliorated EDAC, as evaluated by 320-slice CT scanning with 3D reconstruction.*4 In EDAC or TBM, a CPAP of 7 to 10 cm H2O usually ensures airway patency.24,25 Overall, noninvasive positive-pressure ventilation (CPAP or BiPAP) assistance helps ensure an uncomplicated bronchoscopy in hypercapnic chronic obstructive pulmonary disease (COPD) patients with pneumonia,26 compensates for the hypotonicity of the upper airway muscles in patients with OSA,27 and improves tidal volume and respiratory flow in spontaneously breathing children with easily collapsible upper airways.22

Diagnostic Alternatives

1. CPAP-assisted computed tomography: Noninvasive methods of assessing the degree of collapse and response to CPAP can be offered by CPAP-assisted computed tomography.4 Evaluation of the lung parenchyma may be necessary during CPAP application, especially in patients with COPD. Results from one study showed that a CPAP of 5 cm H2O caused little increase in lung aeration in healthy volunteers and COPD patients, but in a couple of patients with COPD (2 out of 11), CPAP deflated some regions of the lungs. CPAP levels of 10 cm H2O and 15 cm H2O increased the emphysematous zones in all sectors of the lungs, including dorsal and apical regions, in patients with COPD, but caused little hyperaeration predominantly in the ventral areas in healthy volunteers.29 This is potentially harmful, given the already hyperinflated status of a COPD patient’s lungs. Optimal CPAP levels should counteract the increased effort of breathing while improving expiratory airflow to its maximum without causing further hyperinflation.30 Thin HRCT scan slices may better estimate CPAP-induced lung hyperinflation, provided that an appropriate radiologic density threshold is used for quantification of hyperinflated zones.31 This method is useful for EDAC assessment, but not for collecting specimens for microbiologic analysis.

2. Polysomnography: This technique was reportedly useful in a case of EDAC due to tracheobronchomegaly; evidence of both obstructive apnea and hypopnea was found with an apnea-hypopnea index (AHI) of 11, no snoring, and associated oxygen desaturation of 75%. During a second overnight study with nasal CPAP at a pressure of 8 cm, the AHI decreased to 3 and no drop in oxygen saturation was noted.32

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