My Chloe was recently sedated for an MRI. Before any images were taken, the anesthesiologist tried to stabilize Chloe’s breathing for 45 minutes and was unsuccessful. She decided to intubate Chloe. She discovered that Chloe has Subglottic Stenosis (SGS). It can be congenital or acquired. With Chloe, it was probably acquired from her previous intubations. The fact that Chloe suffered from severe reflux probably did not help because it causes the subglottis to be continually bathed in acid, which irritates and inflames the area and prevents it from healing correctly after intubation. The SGS isn’t causing Chloe any problems at the moment, but its definitely something to keep my eye on and to keep in mind for any upcoming surgeries.
INTRODUCTION
Subglottic stenosis (SGS) is a narrowing of the subglottic airway, which is housed in the cricoid cartilage. The subglottic airway is the narrowest area of the airway, since it is a complete, nonexpandable, and nonpliable ring, unlike the trachea, which has a posterior membranous section, and the larynx, which has a posterior muscular section. The term SGS implies a narrowing that is created or acquired, although the term is applied to both congenital lesions of the cricoid ring and acquired SGS.
Acquired SGS is the most common acquired anomaly of the larynx in children and the most common abnormality requiring tracheotomy in children younger than 1 year. Correction of this abnormality requires expanding the lumen of the cricoid area to increase airflow and decrease obstructive breathing. Surgical correction of SGS has been performed with various techniques over the years.
Subglottic stenosis is commonly misdiagnosed as asthma, as both are due to trouble breathing. However, with asthma, patients usually have trouble breathing out, while patients with subglottic stenosis usually have trouble breathing in.
The congenital form is related to inadequate recanalization of the laryngeal lumen after completion of the normal epithelial fusion at the end of the third month of gestation. It can be membranous or cartilaginous. The membranous type often involves the true vocal cords. The cartilaginous type is usually shelf-like at the level of the cricoid and easy to diagnose endoscopically. In other instances the subglottic appearance is normal and only after “sizing” the airway can the appropriate diagnosis be made. The cartilaginous variety of stenosis is very rarely managed successfully with dilation or with laser techniques.
Acquired subglottic stenosis is related to an inconsistent cascade of events that causes 1-8% of infants to develop the condition after prolonged intubation. The most commonly affected area in these children is the cricoid. Proposed theories regarding the etiology and pathogenesis agree many factors are important (i.e. small cricoid, reflux, infection, tube movement and replacement, among others). All forms of subglottic stenosis can be assigned a grade.
History of the Procedure
Early in the 20th century, acquired SGS usually was related to trauma or infection from syphilis, tuberculosis, typhoid fever, or diphtheria. Also, children often had tracheotomies placed that caused laryngeal stenosis. In this era, attempted laryngeal dilation failed as a treatment for SGS.
Acquired SGS occurred increasingly in the late 1960s through the 1970s, after McDonald and Stocks (in 1965) introduced long-term intubation as a treatment method for neonates in need of prolonged ventilation for airway support. The increased incidence of SGS focused new attention on the pediatric larynx, and airway reconstruction and expansion techniques were developed.
Frequency
The frequency of congenital SGS is unknown.
The incidence of acquired SGS has greatly decreased over the past 40 years. In the late 1960s, when endotracheal intubation and long-term ventilation for premature infants began, the incidence of acquired SGS was as high as 24% in patients requiring such care. In the 1970s and 1980s, estimates of the incidence of SGS were 1-8%. In 1998, Choi reported that the incidence of SGS had remained constant at the Children’s National Medical Center in Washington, DC; it was approximately 1-2% in children who had been treated in the neonatal ICU. Walner recently reported that, among 504 neonates who were admitted to the level III ICU at the University of Chicago in 1997, 281 were intubated for an average of 11 days, and in no patient did SGS develop over a 3-year period. In 1996, a report from France also described no incidence of SGS in the neonatal population who underwent intubation with very small endotracheal tubes (ie, 2.5-mm internal diameter) in attempts to prevent trauma to the airway.
Etiology
The cause of congenital SGS is in utero malformation of the cricoid cartilage.
The etiology of acquired SGS is related to trauma of the subglottic mucosa. Injury can be caused by infection or mechanical trauma, usually from endotracheal intubation but also from blunt, penetrating, or other trauma. Historically, acquired SGS has been related to infections such as tuberculosis and diphtheria. Over the past 40 years, the condition typically has been related to mechanical trauma.
Factors implicated in the development of SGS include the size of the endotracheal tube relative to the child’s larynx, the duration of intubation, the motion of the tube, and repeated intubations. Additional factors that affect wound healing include systemic illness, malnutrition, anemia, and hypoxia. Local bacterial infection may play an important roll in the development of SGS. Gastroesophageal reflux (GERD) may play an adjuvant role in the development of SGS because it causes the subglottis to be continually bathed in acid, which irritates and inflames the area and prevents it from healing correctly. A systemic or gastrointestinal allergy may cause the airway to be more reactive, creating a greater chance of developing stenosis.
Pathophysiology
Acquired SGS often is caused by endotracheal intubation. Mechanical trauma from an endotracheal tube, as it passes through or remains for long periods in the narrowed neonatal and subglottic airway, can lead to mucosal edema and hyperemia. These conditions then can progress to pressure necrosis of the mucosa. These changes have been observed within a few hours of intubation and may progress to expose the perichondrium of the cricoid cartilage. Infection of the perichondrium can result in a subglottic scar. This series of events can be hastened if an oversized endotracheal tube is used. Always check for an air leak after placing an endotracheal tube because of the risk of necrosis of the mucosa, even in short surgical procedures. This practice is common among anesthesiologists. Usually, the pressure of the air leak should be less than 20 cm of water, so that no additional pressure necrosis occurs in the mucosa of the subglottis.
Clinical History
Children with SGS have an airway obstruction that may manifest in several ways. In neonates, SGS may manifest as stridor and obstructive breathing after extubation that requires reintubation. At birth, intubation in most full-term neonates should be performed with a 3.5-mm pediatric endotracheal tube. If a smaller-than-appropriate endotracheal tube must be used, narrowing of the airway may be present, which could suggest SGS.
The stridor in SGS usually is biphasic. Biphasic stridor can be associated with glottic, subglottic, and upper tracheal lesions. Inspiratory stridor usually is associated with supraglottic lesions; expiratory stridor usually is associated with tracheal, bronchial, or pulmonary lesions.
The level of airway obstruction varies depending on the type or degree of SGS. In mild SGS, only exercise-induced stridor or obstruction may be present. In severe SGS, complete airway obstruction may be present and may require immediate surgical intervention.
Depending on the severity, SGS can cause patients to have decreased subglottic pressure and a hoarse or a weak voice. Hoarseness or vocal weakness also can be associated with glottic stenosis and vocal cord paresis or paralysis.
Always ask about a history of recurrent croup. A child with an otherwise adequate but marginal airway can become symptomatic with the development of mucosal edema associated with a routine viral upper respiratory infection (URI). Children with these conditions may have subglottic narrowing and an evaluation of the airway is appropriate.
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