Pulmonary Medicine

Disorders of the Central Airways and Upper Airway Obstruction

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What every physician needs to know:

The upper airway is defined as the airway segment between the nose or mouth and the main carina, which is located at the lower end of the trachea. The central airways refer to the trachea and the main-stem bronchi. Unlike the lower conducting airways, such as the main, lobar, and segmental bronchi, the upper airway has no collateral ventilation. Therefore, obstruction of the upper airway or central airway is unique in that any obstruction, whether acute (occurring within minutes) or chronic (developing over weeks or months), may be catastrophic. Clinically significant obstruction may occur at any site along the upper airway and result in asphyxia and death; recognition and treatment can be life-saving.

Classification:

The upper airway includes four compartments: the nose (functional during nasopharyngeal breathing) and mouth (functional during oropharyngeal breathing), the pharynx, the larynx, and the trachea. Because of their parallel anatomic arrangement, the mouth and nose are rarely the site of upper airway obstruction, except in cases of massive facial trauma.

The upper airway is comprised of extra-thoracic and intra-thoracic portions, with the thoracic inlet as the point of demarcation. Consideration of this anatomic distinction is important in the physiologic assessment of patients suspected of having upper airway obstruction. Differentiation between a dynamic (or variable) obstruction and an anatomical (or fixed) obstruction to airflow is also important in accurately assessing suspected upper airway obstruction.

Obstruction of the upper airway may occur acutely and result in respiratory distress and death within minutes or it may evolve chronically, resulting in progressive dyspnea and exercise intolerance. Chronic obstruction may also result in acute respiratory distress when a critical narrowing of the airway is reached through progression of the primary cause of the obstruction or as a result of mucus plugging or bleeding.

A variety of causes should be considered when acute upper airway obstruction is suspected:

  • infection (e.g., epiglottitis, Ludwig's angina, croup)

  • aspiration (e.g., foreign body)

  • angioedema (e.g., allergic, hereditary, drug-induced)

  • iatrogenic (e.g., instrumentation, post-surgical)

  • hemorrhage (e.g., tumors, blood dyscrasia)

  • inhalation injury (e.g., explosion, fire, industrial accident)

  • blunt trauma (e.g., motor vehicle accident, physical attack)

  • neuromuscular disease (e.g., myasthenic crisis, laryngeal-pharyngeal dystonia)

A broad differential diagnosis should be considered when chronic upper airway obstruction is suspected:

  • infection (e.g., tuberculosis, rhinoscleroma)

  • tumor (e.g., squamous cell carcinoma of larynx and trachea, hamartoma, hemangioma)

  • collagen vascular disease (e.g., Granulomatosis with polyangiitis (GPA) relapsing polychondritis)

  • sarcoidosis

  • amyloidosis

  • post-intubation (e.g., tracheomalacia, tracheal stenosis)

  • mediastinal mass (e.g., thymoma, lymphadenopathy)

  • vascular abnormality (e.g., vascular ring, aortic aneurysm)

  • esophageal disorder (e.g., achalasia, Zenker's diverticulum)

  • laryngeal dysfunction (e.g., vocal cord paralysis, vocal cord dysfunction, laryngocoele)

  • neuromuscular disease (e.g., Parkinson's disease, bulbar palsy)

  • tracheobronchopathia osteochondroplastica

  • idiopathic (e.g., sub-glottic stenosis)

  • Tonsillar enlargement in children

Central airway obstruction is a subset of upper airway obstruction and involves the trachea and main-stem bronchi. The etiologies are divided into malignant and non-malignant.

Are you sure your patient has an upper airway obstruction? What should you expect to find?

The major symptom of upper airway obstruction is shortness of breath. When the obstruction is acute, such as with anaphylaxis-induced laryngospasm, sudden dyspnea or even suffocation may result.

When upper airway obstruction occurs over time, such as with post-intubation tracheal stenosis, patients first experience dyspnea with exertion. With chronic obstruction, a significant degree of anatomic obstruction typically precedes overt symptoms. For example, when exertional dyspnea occurs, the airway diameter is likely to be reduced to about 8mm. Dyspnea at rest develops when the airway diameter reaches 5mm. As the mean tracheal diameter measured at the thoracic inlet is 18.2mm (standard deviation ±1.2mm) in men and 15.2mm (standard deviation, ±1.4mm) in women, considerable airway compromise may occur before symptoms arise.

Occasionally, shortness of breath is accentuated with assumption of a specific body position, such as a reclining position. Upper airway obstruction in the recumbent position may cause disrupted sleep and, when advanced, may result in sleep apnea syndrome. The syndrome resolves completely when the obstruction is relieved. Therefore, daytime somnolence may be a prominent feature of upper airway obstruction.

In severely affected patients with chronic upper airway obstruction, cor pulmonale may occur as a result of chronic hypoxemia and hypercarbic respiratory failure. Signs of right-sided heart failure, such as hepatic congestion and ankle edema, may appear. In addition, airway narrowing often coincides with the appearance of stridor.

Beware: there are other diseases that can mimic an upper airway obstruction.

The symptoms of dyspnea and noisy breathing are identical to those experienced by patients with lower airway diseases, such as asthma and COPD, and these similarities can lead to diagnostic confusion. Since asthma and COPD are considerably more common in the general population than is upper airway obstruction, they may be assumed to be the cause of symptoms in patients with undiagnosed upper airway obstruction. Consequently, the diagnosis of upper airway obstruction may be delayed, resulting in possible catastrophic consequences.

When upper airway obstruction occurs acutely, asphyxia and death may result within minutes to hours. Treatment for acute asthma or COPD exacerbation is ineffective. When upper airway obstruction develops slowly, a delay in diagnosis may predispose patients to unnecessary complications, such as bleeding or respiratory failure, and in the case of an upper airway malignancy, to advanced and incurable disease.

Can the presence of stridor distinguish between upper and lower airway obstruction?

Although it should be easy to distinguish stridor from lower airway sounds, audio recordings from the neck and chest have shown that the sound signals from the asthmatic wheeze and stridor are of similar frequency. This explains why errors in diagnosis may be made and why upper airway obstruction that is due to a tumor or foreign body is often mistakenly treated as asthma.

Stridor versus wheeze: diagnostic clues to differentiate the two

Certain clinical findings may help distinguish between stridor and wheeze:

  • The musical sounds of stridor, which usually occur during inspiration, are heard loudest in the neck. Wheezing, which is characteristic of diffuse lower airway narrowing, occurs predominantly during expiration and gets louder at end-expiration.

  • Maneuvers that increase flow, such as voluntary hyperventilation induced by panting, accentuate stridor.

  • Neck flexion may change the intensity of stridor, suggesting a thoracic outlet obstruction.

  • If the obstructing lesion is below the thoracic inlet, both inspiratory and expiratory stridor may be heard.

  • The character of a patient’s voice may be a clue to an upper airway obstruction. Hoarseness may be a sign of a laryngeal abnormality, and muffling of the voice without hoarseness may indicate a supra-glottic process.

How and/or why did the patient develop an upper airway obstruction?

The sudden onset of respiratory distress and stridor should suggest an upper airway obstruction. However, the causes of upper airway obstruction are numerous, and clinical history is essential in establishing a definitive diagnosis. This axiom is true for patients who develop chronic upper airway obstruction, who are likely to give a history of progressive dyspnea on exertion. A careful assessment of co-morbidities that may predispose a patient to this complication is important.

Historical clues and presentation in acute upper airway obstruction:

Epiglottitis

Epiglottitis has become more common in adults than in children, likely reflecting recent trends in vaccination using H. influenzae type b vaccine. The dominant symptom is odynophagia, which occurs in more than 90 percent of patients. Other common symptoms and signs include drooling, fever, muffled voice, and dyspnea. Upper airway obstruction in the epiglottis may be life-threatening.

Ludwig's angina

Upper airway obstruction may occur when infection spreads along the planes formed by the deep cervical fascia. Infection in the retropharyngeal space, peri-tonsillar, submandibular, pre-vertebral, or visceral vascular spaces in the neck may spread from one area to another, causing a life-threatening event. If a patient presents with sore throat, difficulty swallowing, neck swelling, or fever and develops progressive dyspnea, deep cervical space infection should be considered. Antecedent trauma, such as mandibular fracture, head and neck malignancy, intravenous drug abuse, and immune suppression, are known risk factors.

Lemierre's syndrome

Lemierre's syndrome is a rare complication of oro-pharyngeal infection in which septic phlebitis of the internal jugular vein complicates the infection, possibly resulting in septic emboli to the lungs and joints. Most often, the causative organism is Fusobacterium necrophorum, an obligate anaerobic gram negative rod.

Laryngopyocele

Laryngopyocele arises from secondary infection of a pre-existing laryngocele. A laryngocele is congenital or acquired anomalous dilated laryngeal ventricle that communicated with the cavity of the larynx. Imaging can identify a fluid-filled or air and fluid-filled density emanating from the laryngeal ventricle and extending supero-laterally into the para-glottic fat. Radiographic enhancement that demonstrates a thick rim in the structure indicates underlying inflammation.

The diagnosis is a rare cause of acute airway obstruction. Nonspecific clues to the diagnosis include odynophagia and symptoms of aspiration.

Foreign body aspiration

Foreign body aspiration may lead to sudden respiratory distress or may present more sub-acutely. Sudden choking, cough, stridor, and shortness of breath and collapse while eating suggest the classic "café coronary." The syndrome is especially notable with advancing age, particularly in those with depressed mental status or an impaired swallowing reflex. Non-food aspiration, especially in older children and adolescents, should also be considered when similar symptoms occur.

Anaphylaxis

Anaphylaxis may evolve in minutes to hours. The diagnosis is primarily based on the clinical history of recent exposure. The number of potential triggers is extensive; ingestion of peanuts, tree nuts, shellfish, fish, milk, and eggs is most commonly reported. Hymenoptera stings, reactions to radioactive dyes, or ingestion of medication (e.g., aspirin, NSAIDs, ACE-inhibitors, opioids) are other common factors. Involvement of the respiratory tract occurs in approximately 70 percent of patients.

A clue to diagnosis is involvement of other target organs, including skin (80-90% of episodes), gastrointestinal tract (30-45% of episodes), heart and vasculature (10-45% of episodes), and CNS (10-15% of episodes). Therefore, in addition to respiratory symptoms, the presence of hives, itching, flushing, nausea, vomiting, diarrhea, abdominal pain, dizziness, shock, and headache should suggest anaphylaxis; when these symptoms (especially skin involvement) are absent, the diagnosis becomes more difficult to make.

Iatrogenic causes

Iatrogenic causes of acute upper airway obstruction should be considered when there has been recent instrumentation or surgery. Complications of endotracheal intubation, which are usually associated with emergency resuscitation, may occur when the endotracheal tube is advanced too far or when esophageal intubation occurs inadvertently. Postoperative hemorrhage following tracheostomy or head and neck surgery is another cause.

Inhalational injuries

Inhalational injuries are most often seen following house or building fires or following industrial accidents. Edema of the upper airways may result in either immediate airway closure or airway obstruction whose onset is delayed for several hours. Clues to the diagnosis include cutaneous burns, singeing of nasal hairs, hoarseness, and stridor.

Hemorrhage

Hemorrhage may cause upper airway obstruction following neck surgery, carotid angiography, or necrotizing infection. Spontaneous hemorrhage may be a complication of anticoagulant therapy or severe thrombocytopenia; it has also been reported in hemophiliacs. Blunt or penetrating trauma may result in hemorrhage and tissue disruption that can eventuate in severe respiratory compromise.

Neurologic disorders: A number of neurologic disorders may affect the upper airway, including neuromuscular diseases involving the bulbar muscles, vocal cord paralysis, and laryngeal nerve damage that are due to tumor or trauma. Laryngo-pharyngeal dystonia may cause severe acute airway compromise, although the dyspnea associated with this disorder usually occurs gradually. Involvement of the facial, lingual, masticatory, and laryngeal muscles has been reported in up to 75 percent of cases. Dyspnea is caused by intermittent glottic and subglottic obstruction that arises from both laryngeal and supra-laryngeal/pharyngeal muscle spasms. The disorder may be seen as a complication of antipsychotic medications (e.g., neuroleptics, such as chlorpromazine and haloperidol).

Historical clues and presentation in chronic upper airway obstruction:

Chronic airway infection, tumors of the upper airways may invade the upper airways and, when advanced, may cause upper airway obstruction. The presenting symptoms of tumors of the upper airway include chronic cough, hoarseness, hemoptysis, dysphagia, and odynophagia, in addition to progressive dyspnea. These symptoms should prompt thorough investigation of the larynx and the lower airways.

A number of collagen vascular diseases may affect the upper airway and cause chronic airflow obstruction, including Wegener's granulomatosis, relapsing polychondritis, extrathoracic airway obstruction, Sjögren's syndrome, sarcoidosis, inflammatory bowel disease and amyloidosis.

Granulomatosis with Polyangiitis (GPA; formerly Wegener's granulomatosis) may cause irreparable damage to the upper airways, leading to chronic airflow obstruction. The disease may be limited to the respiratory tract; involvement of the trachea has been described in the absence of pulmonary disease. Kidney, skin, nervous system, and cardiac involvement point to a multi-systemic collagen vascular disorder.

Relapsing polychondritis may lead to life-threatening upper airway obstruction. Acute inflammation of the cartilage and perichondral tissue results in destruction of airway cartilage. The larynx and subglottic trachea are usually the initial targets, but extensive involvement of the distal trachea and bronchi may also occur. Ear pain, the most common presenting symptom, is seen in more than 90 percent of cases. Signs of auricular chondritis are evident on physical examination (Figure 1). Ocular, auricular, and nasal cartilage damage may also occur.

Figure 1.

"Cauliflower ear" deformity of patient with relapsing polychondritis caused by repeat episodes of acute chondritis.

Rheumatoid arthritis is a collagen vascular disorder where extra-thoracic airway obstruction that is due to involvement of the crico-arytenoid joints has been described. Sore throat, hoarseness, and difficulty inspiring are predictive of this complication. Upper airway obstruction, when observed, usually occurs during an acute exacerbation of rheumatoid arthritis. Symptoms may be slowly progressive or abrupt. Episodes of airway obstruction may also occur with rheumatoid arthritic involvement of the temporomandibular joint, causing pharyngeal obstruction.

In Sjogren's syndrome, the predominant presenting symptom is xerostomia, but airway compromise that is due to mucosal dryness, crusting of tenacious secretions, mucosal ulcerations, and edema of the vocal cords has been reported.

Sarcoidosis typically involves the lungs and intrathoracic lymph nodes, and eye and skin involvement are common. Granulomatous involvement of the upper airways, which occurs infrequently, may lead to scaring, stenosis, and airflow obstruction.

Inflammatory bowel diseases, especially ulcerative colitis (rather than Crohn's disease), may affect the airways, causing tracheal ulcers and tracheal stenosis. The presence of bowel disease almost always precedes the airway disease.

Tracheobroncheal amyloidosis is the most common form of pulmonary amyloidosis. It may present as multiple, tumor-like masses or plaques on the walls of the trachea, and the resulting airway narrowing and airflow obstruction may be severe. When hoarseness is present, laryngeal involvement should be suspected. Occasionally, macroglossia may occur, but airway involvement with amyloid deposits is usually not suspected until laryngoscopic or bronchoscopic investigation is conducted.

Iatrogenic causes include injury from prior endotracheal tube intubation or tracheostomy, especially when emergent or traumatic. Contemporary use of low-pressure, cuffed endotracheal tubes has resulted in a lower incidence of tracheal injury than has been experienced with older tubes. The low-pressure cuffs are less likely to cause pressure-induced ischemic necrosis of the airway. Tracheal stenosis or tracheomalacia can be seen as complications. Tracheomalacia occurs when pressure on the cartilaginous rings causes them to soften and fragment. Post-intubation tracheal stenosis occurs when granulation tissue and fibrosis arise from healing of the ulcerated, necrotic lesions. Concentric or eccentric wall thickening may occur, reducing the tracheal lumen (Figure 2). Risk factors for tracheal injury include prolonged intubation, corticosteroid therapy, positive pressure ventilation, and infection.

Figure 2.

Post-intubation tracheal stenosis causing fixed upper airway obstruction

Rarely, mediastinal masses, such as lymphadenopathy, intrathoracic goiter, and vascular abnormalities, the last of which include aortic aneurysms, may become large enough to obstruct the trachea. Pain may alert the clinician to these conditions. Other vascular abnormalities, such as vascular rings caused by a double or right-sided aortic arch, may be silent for years until tracheal compression or tracheomalacia occurs.

Esophageal disorders: An extremely distended esophagus that is due to either malignant (e.g., carcinoma) or benign (e.g., achalasia) obstruction may cause tracheal obstruction. Difficulty swallowing and nocturnal cough from aspiration may be clues to the diagnosis (Figure 3).

Figure 3.

Large dilated esophagus compressing the trachea and causing upper airway obstruction

Vocal cord dysfunction is a cause of intermittent dyspnea of extra-thoracic origin. Potential causes include postnasal drip leading to increased laryngeal sensitivity and subsequent hyper-responsiveness and gastroesophageal reflux of gastric acid causing laryngeal mucosal damage. A subset of patients likely have psychogenic stridor and wheezing, constituting a functional disorder. This subset often involves other psychiatric issues, such as disorders of affect or personality or post-traumatic stress disorder (PTSD). The diagnosis may be suspected in an abnormal flow volume loop that shows a marked reduction in inspiratory flow. Confirmation is based on laryngoscopy that demonstrates paradoxical closure of the vocal cords during inspiration (Figure 4).

Figure 4.

Vocal cord dysfunction: Flow volume loop and laryngoscopic appearance

Tracheobronchopathia osteochondroplastica is a rare disorder of the large airways (the trachea and, less often, the larynx) that is characterized by submucosal cartilaginous and bony nodules protruding into the lumen of the airway. As with relapsing polyarthritis, involvement of the posterior membrane of the trachea does not occur, as this portion of the trachea has no cartilage (Figure 5).

Figure 5.

TPO Saggital CT scan and bronchoscopic findings

Idiopathic subglottic stenosis has been described, but no diagnostic clues are helpful.

What laboratory studies should you order to help make the diagnosis, and how should you interpret the results?

The patient with acute upper airway obstruction presents with dyspnea. The patient's medical history is most useful in distinguishing the cause of acute upper airway obstruction.. Supplementing the history, very useful diagnostic information is obtained from routine pulmonary function testing and radiographic studies of the chest and upper airways. Routine blood tests, serologic studies may be useful in diagnosis of infection and collagen vascular diseases respectively, and sputum cytology may be helpful in a search for suspected malignancy.

What imaging studies will be helpful in making or excluding the diagnosis of acute upper airway obstruction?

As dyspnea and respiratory distress are the predominant symptoms of both acute and chronic upper airway obstruction, roentgenographic assessment should be performed immediately in the stable patient. When anaphylaxis or foreign body aspiration is suspected, immediate treatment is warranted, as a delay for completing radiographic studies may be dangerous and uninformative. In less emergent settings, radiographic evaluation is recommended as follows.

Radiographic assessment of the patient with suspected acute upper airway obstruction

In stable patients, lateral views of the neck and standard chest films should be part of the initial evaluation. Swelling of upper airway structures, such as the epiglottis, aryepiglottic folds, and uvula, may be detected on plain radiographs. Foreign bodies, cellulitis, and abscess formation of deep cervical spaces may be seen on lateral views of the neck.

Contrast-enhanced computed tomography (CECT) is usually necessary in the evaluation of acute upper airway obstruction, especially when deep neck infection is suspected; serial scanning may be useful in monitoring the patient's response to treatment. CECT, coupled with physical examination, has an accuracy rate of 89 percent in differentiating a drainable abscess from cellulitis.

Ultrasound is more accurate than CECT in differentiating a drainable abscess from cellulitis in patients with deep neck infection. Ultrasound technology is portable and inexpensive, and it avoids exposing the patient to radiation. However, accurate application of the technique and its interpretation are subject to the skill level of the operator.

Magnetic resonance imaging (MRI) provides better soft tissue definition than CECT does, and it avoids exposing the patient to radiation. However, MRI is expensive and time-consuming. Magnetic resonance angiography may be useful in evaluating vascular complications of certain causes of upper airway obstruction, such as thrombophlebitis seen in Lemierre's syndrome, or vascular aneurysms.

Radiographic assessment of the patient with suspected chronic upper airway obstruction

CT scanning is the standard imaging modality for evaluation of chronic upper airway obstruction, as the technique is highly accurate (sensitivity, 90-94%) for depicting focal abnormalities in the central airways. However, conventional CT scanning is imprecise in characterizing bronchial abnormalities depicted on bronchoscopy. The use of multiplanar CT techniques, coupled with three-dimensional reconstructions, provides accurate anatomic delineation of the trachea and larynx. Helical CT scanning incorporates volume averaging techniques during a single breath-hold, thereby eliminating respiratory motion-related artifact. Overlapping thin CT slices can be reconstructed from the raw data, enabling creation of high-quality images.

With recent advances in computer techniques, CT bronchography (or virtual bronchoscopy) (Figure 6) and three-dimensional, external renderings of the tracheobronchial tree may be derived from helical CT data. The resulting images are remarkably high-quality reproductions of airway anatomy.

Airway wall thickening, narrowing of the tracheal air column, calcifications, extrinsic compression of the airway, intraluminal lesions, and airway fistulas may be identified (Figure 7).

Figure 6.

Reconstructed CT scan showing virtual bronchoscopy image of the trachea. Patient had tracheal narrowing from relapsing polychondritis.

Figure 7.

Idiopathic subglottic stenosis causing upper airway obstruction.

Three-dimensional images may help surgeons and interventional bronchoscopists select the proper procedures for diagnosis and treatment of upper airway obstruction. Intravenous contrast agent is not needed in assessment of suspected benign lesions; however, use of contrast agent may be useful in distinguishing suspected malignancy from adjacent lymph nodes. Scanning during a dynamic expiratory maneuver may help identify focal airway collapse that is due to tracheomalacia.

What imaging studies will be helpful in making or excluding the diagnosis of chronic upper airway obstruction?

Multidetector-computed tomography is the study of choice in evaluating chronic upper airway obstruction.

What non-invasive pulmonary diagnostic studies will be helpful in making or excluding the diagnosis of upper airway obstruction?

The diagnosis of acute upper airway obstruction must be established and managed immediately. Non-invasive pulmonary diagnostic tests are not indicated in this setting. The diagnosis of chronic upper airway obstruction may incorporate non-invasive pulmonary function tests. Spirometry, including measurements of maximal inspiratory and expiratory flows, is the most commonly used test. However, the forced vital capacity (FVC) and forced expiratory volume in one second (FEV1) may be normal in upper airway obstruction.

Critical in evaluating pulmonary function tests in the setting of suspected upper airway obstruction is inspection of the configuration of the flow-volume loop (FVL). The FVL is created by plotting maximal inspiratory and maximal expiratory flows against lung volume. Inspection of the FVL may be helpful in determining the location of upper airway obstruction and in monitoring its response to treatment. Although the FVL is easily generated and is potentially very informative, it is not very sensitive in diagnosing upper airway obstruction. The diameter of the upper airway may have to be narrowed to less than 8mm in order to produce flow limitation. Therefore, if the FVL is normal, further procedures, such as laryngoscopy, or radiographic studies should be considered when upper airway obstruction is suspected.

Differentiating extra and intra-thoracic upper airway obstruction

The upper airway includes the extra-thoracic airway, which extends from the mouth to the sternal notch, and the intra-thoracic airway, which extends from the sternal notch to the main carina. Inspection of the flow-volume loop may help localize the site of obstruction to the extra-thoracic or intra-thoracic airway (Figure 8).

Figure 8.

Normal configuration of the flow volume loop

The flow-volume pattern seen with variable extra-thoracic upper airway obstruction is characterized by limitation of maximal inspiratory flow (“clipping” of the inspiratory flow-volume loop) and the contour of the expiratory side of the loop is normal. As a reflection of the disruption of inspiratory flow, a ratio of Forced Expiratory Flow at 50 percent of Vital Capacity (FEF-50) to Forced Inspiratory Flow at 50 percent of Vital capacity (FIF-50) may exceed 2. Vocal cord dysfunction, paralysis, or edema may produce this pattern (Figure 9).

Figure 9.

Variable extra thoracic upper airway obstruction (extrathoracic portion of trachea)

Pathophysiology of variable extra-thoracic airway obstruction: During inspiration, the diaphragm lowers intra-thoracic and intra-airway pressures. The lowering of intra-airway pressure provides a “sucking” force that promotes airway collapse. In the intra-thoracic upper airway, the low intra-airway pressure is countered by the lower intrathoracic pressure so transmural pressure is positive, and the intrathoracic upper airway resists collapse during inspiration. By contrast, the extra-thoracic upper airway is not subject to intrathoracic pressure; at this site, the negative intraluminal pressure is not countered by negative intrathoracic pressure. Hence, transmural pressure is negative, and the extra-thoracic upper airway is subject to collapse during inspiration.

Upper airway muscle activity, which may be tonic or phasic, is critical in maintaining a patent extra-thoracic upper airway. Upper airway muscle activity must be coordinated with diaphragm activation so, without phasic activity, the negative intramural pressure generated by the diaphragm is unopposed, promotes airway collapse, and increases airways resistance. The increase in airways resistance further promotes collapse by increasing the effort needed to inhale a given volume. To mitigate the effects of low intramural pressure, reflex activation of the upper airway dilator muscle occurs in response to a reduction in intraluminal pressure.

During sleep, a disproportionate reduction in neural drive to the upper airway muscle relative to the diaphragm may be observed. This reduction in upper airway dilator muscle tone promotes airway collapse, as the negative intraluminal pressure that occurs during inspiration is unopposed.

The flow-volume pattern seen with intra-thoracic upper airway obstruction is characterized by limitation of maximal expiratory flow (“clipping” of the expiratory flow-volume loop), a pattern referred to as variable intra-thoracic upper airway obstruction, as the contour of the inspiratory side of the loop is normal. Thus, the ratio of FEF-50 to FIF-50 is reduced to values less than 0.3. Intraluminal tumors involving the lower trachea or tracheomalacia may produce this pattern (Figure 10).

Figure 10.

Variable intra- thoracic upper airway obstruction. Patient with large tracheal tumor

Pathophysiology of variable intrathoracic obstruction: During expiration, the expiratory muscles increase intra-thoracic and intra-airway pressures. Because intra-airway pressure is dissipated by resistive forces as air moves downstream from the alveolus to the mouth, intra-airway pressure is lower than intra-thoracic pressure. Therefore, transmural pressure is negative in the intrathoracic upper airway and is subject to collapse during expiration. By contrast, the extra-thoracic upper airway is not subject to intrathoracic pressure. At this site, a positive intraluminal produces a positive transmural pressure that promotes expansion of the airway.

The flow-volume pattern seen with fixed upper airway obstruction is characterized by limitation of both maximal inspiratory and expiratory flow rates (“clipping” of the inspiratory and expiratory sides of the flow –volume loop). With a fixed pattern, the site of upper airway obstruction may be either intra- or extra-thoracic (Figure 11). A mass compressing the trachea (e.g., intrathoracic goiter or lymphoma) may produce this pattern.

Figure 11.

Flow volume loop of patient with fixed upper airway obstruction

What diagnostic procedures will be helpful in making or excluding the diagnosis of upper airway obstruction?

In the acute setting, when epiglottitis is suspected, the diagnosis may be confirmed by seeing an erythematous, edematous epiglottis. In adults, the epiglottis may be inspected directly with the aid of a tongue depressor, and flexible nasopharyngoscopy has also been shown to be a safe and effective way to confirm epiglottitis. With other causes of acute upper airway obstruction, instrumentation is rarely indicated and may be contraindicated.

Bronchoscopic and laryngoscopic techniques are useful in evaluating suspected chronic upper airway obstruction. The procedures can be guided by findings on conventional transverse CT scans or virtual bronchoscopic CT studies. Biopsy of any lesions found may lead to accurate pathologic diagnosis.

What pathology/cytology/genetic studies will be helpful in making or excluding the diagnosis of upper airway obstruction?

Pathologic specimens from laryngeal or tracheal biopsies may identify laryngeal and bronchogenic carcinoma.

Primary tracheal tumors

Common examples of primary tracheal tumors include:

  • squamous cell carcinoma (most common)

  • adenoid cystic carcinoma

  • muco-epdermoid tumor

  • hamartoma

  • hemangioma

  • neurogenic tumor

  • granular cell tumor

  • squamous papilloma

  • lymphoma

Diagnoses made by bronchial biopsy

Examples of diagnoses that may be readily established through bronchial biopsy include:

  • amyloidosis (nodules or plaques, positive on Congo red staining)

  • tuberculosis (granulomas, culture organism)

  • rhinoscleroma (granulomas, culture organism)

  • fungal tracheobronchitis (histology shows aspergillus organism)

  • Wegener's granulomatosis (granulomas and vasculitis)

  • sarcoidosis (non-caseating granulomas)

  • relapsing polychondritis (inflammation, fragmentation, and destruction of cartilage)

  • tracheobronchopathia osteochondroplastica (nodules and spicules of bone in submucosa of the trachea)

If you decide the patient has upper airway obstruction, how should the patient be managed?

Management of upper airway obstruction, either acute or chronic, depends on the cause. When airway obstruction is acute (within minutes), no testing is warranted, and immediate treatment is mandatory. When the obstruction evolves over several hours or longer, ancillary studies, such as roentgenograms and blood studies, may be very helpful in targeting therapy. When symptoms of chronic upper airway obstruction progress over months, pulmonary function tests, roentgenographic testing, and endoscopic assessment are helpful in establishing the diagnosis and directing treatment.

Treatment options for acute upper airway obstruction

Acute upper airway obstruction is a medical emergency that requires prompt intervention. Reactions to allergens (e.g., peanuts, medications, bee stings), infections (epiglottitis), or particles and gases (smoke inhalation) may cause acute edema of the throat and larynx. In addition, a foreign body lodged in the throat or larynx may cause acute upper airway obstruction. Treatment consists of interventions designed to restore airway patency, provide adequate oxygenation and ventilation, and alleviate the underlying cause.

Selected clinical examples include use of the Heimlich maneuver in an individual who suddenly is unable to speak while eating (a “café coronary”) may relieve the obstruction.

Use of corticosteroids, antihistamines, H1 and H2 blockers, and subcutaneous epinephrine may alleviate angioedema. These agents are not very effective in ACE-I induced angioedema and hereditary angioedema as it is mediated by the kallikrein- bradykinin pathway. Recent studies have shown newer drugs such as Icatibant and Lanadelumab that mediate this pathway may be effective in both prophylaxis and treatment. Measures like elevating the head of the bed and using humidified oxygen or a mixture of helium and oxygen (Heliox) may permit sufficient time for medications to decrease airway swelling and improve airway patency. Heliox is supplied as a tank of compressed gas composed of 80 percent helium and 20 percent oxygen. Helium is less dense than nitrogen and thus decreases turbulent flow in large airways thereby reducing the work of breathing. The fraction of inspired oxygen in Heliox may be increased to as much as 40 percent to address concurrent hypoxemia.

Performance of endobronchial intubation is usually the definitive means of securing the airway and alleviating acute upper airway obstruction. Emergency tracheostomy may need to be performed if tongue swelling or edema of pharyngeal soft tissue precludes visualization of the vocal cords or placement of an endotracheal tube. If a tracheostomy cannot be performed immediately, cricothyroidotomy may provide short-term airway control.

Treatment options for chronic upper airway obstruction

Both benign and malignant diseases of the upper airways may lead to progressive airway obstruction. Management strategies depend on the cause and extent of disease. Ideally, surgical resection of the obstructing lesion(s) should be considered first. However, if the extent of disease does not allow for complete surgical resection, a number of palliative procedures, including include cryotherapy, laser ablation, endoscopic resection, and stent placement, may used to relieve symptoms and improve short- and long-term outcomes.

Treatment of malignant causes of chronic upper airway obstruction

Two common causes of malignant upper airway obstruction are laryngeal and tracheal carcinomas.

Laryngeal carcinoma

The treatment of head and neck tumors depends on proper staging of the disease (extent of local invasion and nodal metastases) and site of the tumor (supra-glottic, glottic, or subglottic), which may be ascertained using computed tomography. For limited disease, both surgery (endoscopic or open resection) and radiation therapy provide comparable results and spare the larynx. For locally advanced disease, surgery, radiation therapy, and chemotherapy have been employed. Organ-sparing approaches are utilized whenever possible.

Tracheal carcinoma

Squamous cell carcinoma is the most common tracheal tumor, followed by adenoid cystic carcinoma. Surgical resection is the treatment of choice whenever possible, as surgery provides superior results to primary radiation. Post-operative radiation therapy is often employed, but whether survival is enhanced with its use is unclear. When the obstruction is severe, laser resection and tracheal stenting have been used as a bridge to surgery.

Treatment of benign causes of upper airway obstruction

The numerous benign causes of chronic airway obstruction include infectious diseases (e.g., tuberculosis, aspergillosis) and chronic inflammatory diseases (e.g., sarcoidosis, granulomatosis with polyangiitis, relapsing polychondritis). Treatment using anti-infective or anti-inflammatory agents, respectively, is appropriate. However, these conditions may be complicated by development of granulation tissue and fibrosis, and surgical or bronchoscopic procedures may become necessary adjuncts. Depending on the extent of the lesion, resection of the lesion, resection of the involved section of large airway (e.g., with airway stenosis, presence of an inflammatory mass, or an area of tracheomalacia), or tracheal reconstruction using a pericardial or synthetic implant may be warranted.

What is the prognosis for patients managed in the recommended ways?

The prognosis in upper airway obstruction depends on the cause, whether the obstruction is acute or chronic or malignant or benign, and the extent of the disease within the airway; in the case of malignancy, the extent of disease beyond the upper airway is also important. The prognosis is poor with squamous cell carcinoma of the trachea, which carries a five-year survival of approximately 40 percent when the carcinoma is resectable and 7 percent when it is unresectable. The prognosis is generally more favorable when the cause is an infectious or inflammatory disorder.

What are the palliative considerations for patients with chronic upper airway obstruction?

Palliative interventions for patients with chronic upper airway obstruction include balloon dilatation, airway stenting, laser therapy, electrocautery and argon plasma coagulation, cryotherapy, and nocturnal, non-invasive, positive-pressure ventilation.

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