Supraglottic Airway Obstruction

Etiology

Airway obstructions can be acute or chronic. Acute causes of supraglottic obstruction include laryngotracheobronchitis, croup, foreign body aspiration, epiglottitis, angioedema, acute bacterial tracheitis, facial or oral cavity burns, retropharyngeal abscess, and peritonsillar abscess. Chronic causes of supraglottic airway obstruction include laryngomalacia, tracheomalacia, laryngeal cysts, hemangiomas, obstructive sleep apnea, and progressive compression from masses. The obstruction presents as stridor, a harsh vibrating sound heard best during inspiration. The level of obstruction directly corresponds to the intensity of the stridor. Etiology may not be clear on initial presentation, and key factors in history and examination have to be taken into account.[4][5][6]

In obtunded patients, the tongue is the most common cause of upper airway obstruction.[7] Airway obstruction may be classified into either infectious, inflammatory, foreign body, or neoplastic[8]

Inspiratory stridor represents supraglottic obstruction while expiratory stridor originates at or below the glottis level; this can be challenging to accurately assess in a patient breathing extremely rapidly. [9] Transient swelling of the lips, tongue, pharynx and larynx may be caused by angioedema. The swelling may occur rapidly and may emergently obstruct the airway.[10]

In neonates there are several congenital craniofacial anomalies that are associated with airway obstruction. These include craniofacial clefts, Pierre Robin sequence, midface hypoplasia, achondroplasia, and Down syndrome. Such complex patients may have micrognathia, obstructive sleep apnea, or tongue-based airway obstruction, in addition to other neurologic or airway abnormalities that can cause distress.[11]

Epidemiology

Viral agents most often cause upper airway obstruction in the pediatric age group. Bacterial causes such as diphtheria, bacterial tracheitis, and epiglottitis are fairly uncommon especially since the introduction of vaccination with Haemophilus influenzae type b Haemophilus influenzae type b (Hib) and Pneumococcal vaccines. Males are slightly more commonly affected by croup than females. Viruses including parainfluenza and influenza are the most common viral etiological agents.

Foreign body aspirations are common in young children between 2 to 5 years of age. Laryngomalacia is a  chronic cause of upper  airway obstruction and is the most common laryngeal anomaly in the infant age group. It is a frequent cause of "noisy breathing," and does not always cause physiologically significant airway obstruction.[12]

Odynophagia may be indicative of peritonsillar (quinsy), lingual, or retropharyngeal infecetion or abscess formation.[13][14][15][16]

Pathophysiology

Supraglottic obstruction in pediatric patients is more common in children than in adults with a similar illness, and this is due to factors that make the pediatric airway more susceptible to airway obstruction and distress. The pediatric airway is narrower and more prone to obstruction. The relatively high larynx, larger head, large tongue, poor tone, increased compliance which predisposes to kinking, and the narrowest diameter at the cricoid make the pediatric airway increasingly challenging. Air flowing in and out of a more limited airway flows under greater resistance. This results in stridor for upper airway obstruction and wheezing for lower airway obstruction. The presence of stridor indicates the loss of 50% of the airway diameter. [17] Airway inflammation and infections accelerate the edema around the airway. This worsens obstruction and respiratory distress. Most common findings associated are stridor/ noisy breathing, respiratory distress, and tachypnea with improper aeration of the lower airways. Increasing rates of immunizations with Hib and Streptococcal vaccines have resulted in a dramatic decrease in upper airway infections and inflammation. This has led to a dramatic decrease in rates of intubation or invasive interventions to relieve airway obstruction.

Angioedema has multiple mechanisms, but a common presentation.  Histamine-mediated  angioedema results in mast cell degranulation.  Bradykinin-mediated angioedema results from an overproduction of bradykinin due to  either an acquired or inherited C-1 deficiency. [10]Angioedema may also be caused by certain drugs such as angiotensin-converting enzyme inhibitors.[18]

Oversedation during procedures may contribute to airway obstruction and adverse events. In closed-claims analysis, 24% of liability claims during sedation were related to respiratory events.[19]

Neck hematomas may obstruct the upper airway by external compression of the trachea. These may occur post-surgery or due to trauma (blunt and penetrating), or post-extubation.

History and Physical

History depends on the age of presentation of the patient. The younger the patient (in general), the more severe the manifestations of the obstruction. Differences in the presentation also depend on whether the process is acute, subacute, or chronic. The common clinical complaints include a cough, stridor or noisy breathing, difficulty breathing, and respiratory distress. The severity of the respiratory distress can range from mild to moderate or severe. Head bobbing, altered mental status, lethargy, coma, and loss of consciousness are present when the obstruction is severe and impedes breathing. This results in severe hypoxemia or hypocarbia. Initial exam findings include respiratory distress, increased work of breathing, anxiety and chest retractions. Audible stridor is usually appreciated, which worsens with agitation or crying. Wheezing is an uncommon finding with upper airway obstruction and often demonstrates lower airway or chest pathology.

Evaluation

Evaluation should include a complete assessment of the child including the respiratory distress. Work of breathing can be assessed under different categories in categorizing pediatric respiratory distress. This should include the mental status of the child, work of breathing, the use of accessory muscles, respiratory rate, pulse oximetry or end-tidal carbon dioxide monitoring, and auscultation of breath sounds. All parameters should be used in conjunction to evaluate the level of respiratory compromise in a child. Altered mental status and lethargy or fatigue without increased work of breathing or tachypnea should raise concerns for impending respiratory or cardiovascular failure.

The next step in the evaluation of the respiratory status is the assessment of the airway. Various scoring systems are available for evaluation of the airway. Commonly used systems are the Mallampatti scoring system and the ASA (American Society of Anesthesiologists). Assessment of the airway should include management interventions and correction in a step-wise management.

Odynophagia may be seen in patients with abscesses of the oropharynx or hypopharynx.

Treatment / Management

Management of upper airway obstruction depends on the etiology. Primary management should focus on keeping the patient calm, reducing anxiety, and getting the patient in a position of comfort. Airway, breathing, and circulation should be assessed in the primary survey. Any causes of obstruction should be relieved immediately. A foreign body in the oral cavity or upper pharynx can be removed with forceps after direct visualization. Care should be taken to avoid any interventions that may make the child anxious or irritate the child. Avoid intravenous access, painful procedures in patients with acute epiglottitis or tracheitis, to minimize respiratory distress and impending respiratory failure.[9][20]

Corticosteroids have proven to be of benefit for causes related to edema and inflammation of the upper airway in conditions such as croup. The mechanism of action includes anti-inflammatory and reduction of edema. Racemic epinephrine via nebulized route has both alpha and beta action and causes upper and lower airway lumen dilation, which improves air entry and results in a more laminar airflow.

Invasive airway adjuncts such as oropharyngeal and nasopharyngeal airway help in relieving airway obstruction and can be used in cases of tongue edema or inflammation. Positive pressure ventilation is used for relief via bag and mask ventilation if the patient is in severe distress, has increased work of breathing and in patients en route to intubation. Endotracheal intubation can be used if all other methods of relief are unsuccessful and the patient has an impending respiratory failure, is comatose, altered mental status, or has worsening respiratory distress.

Surgical airway with tracheostomy or cricothyroidotomy is used in rare instances when attempts to relieve upper airway obstruction fail. There are instances of facial burns or facial trauma, or in supraglottic foreign body aspiration where obtaining an upper airway adjunct or endotracheal intubation are unsuccessful. The surgical airway should be initiated by an experienced health care provider with adequate training. Best outcomes are achieved when it is initiated promptly with experienced and skilled personnel.

Differential Diagnosis

• Angioedema

• Foreign body

• Ludwig's angina

• Supraglottic, epiglottic or neck abscess

• Tumor

Prognosis

The prognosis will depend on the etiology and the severity of the airway obstruction.

Acute onset supraglottic airway obstruction must be promptly recognized and treated to achieve the best overall prognosis. If the symptoms are mild and recognized early, the patient may be able to protect their own airway while appropriate medical treatment is begun (such as steroids for an inflammatory process, or antibiotics for an infection. If symptoms are evolving or severe, the clinician must have a very low threshold to secure the airway via endotracheal intubation or surgical airway to avoid disaster. Once a secure airway is obtained, the long-term prognosis will depend on treatment of the underlying pathology.

Chronic and gradual supraglottic airway obstruction can have a more mixed prognosis, again depending on the underlying etiology. Laryngomalacia in young children frequently has a very good prognosis, and may not require intervention if symptoms are mild. Supraglottic obstruction from neoplasm will depend on the histology and stage for overall prognosis, which supraglottic scarring after radiation therapy or after inhalational injury can have long-lasting effects, and potentially poor outcomes due to recurrent and refractory stenosis. [21]

Complications

The most feared complication is progressive airway compromise leading to death. Even seemingly mild symptoms can progress rapidly as a patient gradually tires with the increased work of breathing caused by airway obstruction. Once an obstructing airway is diagnoses or suspected, the astute clinician will have a very low threshhold to secure a definitive airway.

Endotracheal intubation (whether direct or fiberoptic) is usually the first planned intervention. Great care should be taken when intubating a potentially obstructed patient, and the physician with the most experience should perform the intubation. Supraglottic masses can be friable, leading to bleeding into the airway and potential inability to secure an airway. Foreign bodies may become dislodged and completely obstruct the airway. The safest place to perform such an intubation is in the Operating Room with a tracheostomy kit open and available, but the patient's impending airway may not always allow for transport to the OR. [22]

If endotracheal intubation is deemed unsafe or impossible, a controlled awake tracheostomy is always preferred over an emergent surgical airway (cricothyrotomy or emergent tracheostomy). The patient can be taken to the OR and a controlled tracheostomy performed under local anesthesia. This can help to minimize the potential complications of tracheostomy, namely bleeding, pneumothorax, and failure to locate the airway (insertion of the tracheostomy tube into a false-passage).[23]

The potential complications from an emergent surgical airway include failure of the procedure (failure to enter the airway lumen in time), bleeding, and pneumothorax. [24]