Introduction
Over the past few decades the instruments available for examining the airway have evolved to become increasingly smaller while providing better optical resolution. It is now possible to directly evaluate the airway of even the smallest premature infant. The optimal approach to airway evaluation depends upon the indication for the procedure, the risk of adverse effects, and the magnitude of potential benefit. This chapter will assist those caring for critically ill neonates in determining which diagnostic modalities will obtain the most relevant information while minimizing risk to the patient.
Flexible Nasopharyngolaryngoscopy in the Neonate
Indications
Flexible laryngoscopy is utilized as a diagnostic tool to assess pathology at or superior to the glottis. This procedure may be performed at the bedside during wakefulness or sleep. It is noninvasive with relatively low risk to the patient as sedation is not necessary.
Flexible laryngoscopy is valuable for narrowing the differential diagnosis in infants with noisy breathing. The evaluation begins at the nares and proceeds through the nasal turbinates to the choana. Because neonates are obligate nasal breathers, severe nasal obstruction can lead to significant respiratory distress with cyclical cyanosis and feeding difficulties. Narrowing of the pyriform aperture, known as congenital nasal pyriform aperture stenosis, is a rare cause of severe nasal obstruction in the neonate. Choanal atresia is a congenital anomaly representing complete obstruction of the nasal airway with an incidence of 1 in 10,000 live births. Infants typically experience severe respiratory distress, especially when it is bilateral (50% of cases). It can be bony or membranous or have features of both.
After the laryngoscope is passed through the nasopharynx, the oropharynx and larynx can be examined. Obstruction at the level of the supraglottic or glottic structures results in inspiratory stridor. The most common cause of stridor in infants is laryngomalacia, which in severe cases presents with dyspnea, feeding difficulties, failure to thrive, dysphagia, and obstructive sleep apnea. It is the result of a congenital abnormality of the laryngeal cartilage or its supportive muscle tone resulting in dynamic collapse of the supraglottic structures during inspiration. Severity initially worsens with growth, but in most cases it resolves between 6 and 18 months of age. Treatment of laryngomalacia is dependent upon the severity of symptoms. Those with mild to moderate laryngomalacia may be managed by observation. Medical therapies can improve symptoms in those with concurrent gastroesophageal reflux disease (GERD). Surgical management with supraglottoplasty can resolve the associated respiratory and feeding problems.
Vocal cord paralysis (VCP) is the second most common laryngeal anomaly identified in neonates. Unilateral VCP often results from iatrogenic injury during cardiothoracic surgery or ligation of a patent ductus arteriosus. It may also be idiopathic or result from neurologic disorders. Iatrogenic unilateral VCP frequently resolves with time, and regular follow-up with repeated endoscopic examinations is recommended prior to considering surgical interventions. Bilateral VCP is less common, usually congenital, and associated with other anomalies in 50% of cases. It presents at birth with respiratory compromise and either inspiratory or biphasic stridor. Infants with unilateral VCP typically have a hoarse cry, whereas those with bilateral VCP vocalize well.
Flexible laryngoscopy is also helpful in differentiating the etiology of hoarse cry in neonates. Hoarse cry may develop following endotracheal intubation as a consequence of glottic edema or granulomata. In the majority of cases, these problems resolve spontaneously or with management of coincident GERD.
Risks, Contraindications, and Limitations
Flexible laryngoscopy, when performed correctly, is a relatively low-risk procedure. Minor risks include vasovagal reactions resulting in bradycardia and laryngospasm. They generally resolve with the removal of the laryngoscope. Maintaining a superior location of the scope and avoiding contact with the glottic structures helps prevent laryngospasm. Coagulopathies are considered a relative contraindication, as the risk of mucosal bleeding from the nose must be weighed against the anticipated benefit of the procedure. The presence of an endotracheal tube substantially limits the value of this procedure. While the nasal airway can still be visualized well, useful information about the larynx is rarely obtained.
Equipment
Necessary equipment required for flexible nasopharyngolaryngoscopy (NPL) includes only a light source and the scope itself. At our institution, the 2.2-mm flexible nasopharyngolaryngoscope is used most often in neonates. Use of “antifog” solutions or alcohol swabs minimizes condensation on the objective lens of the scope and improves visualization.
Direct Microlaryngoscopy and Rigid Bronchoscopy in the Neonate
Indications
Direct rigid telescope microlaryngoscopy and rigid bronchoscopy (ML&B) can be useful as a diagnostic and therapeutic tool for upper airway and subglottic pathology ( Fig. 13-1 ). In contrast to bedside flexible laryngoscopy, general anesthesia is required. Evaluation with ML&B should be considered when a need for surgical intervention is determined based on findings during NPL or when better visualization of the airway is required.
If vocal cord immobility has been established, arytenoid mobility should be assessed by palpation during microlaryngoscopy to determine if the cord mobility is impaired as a result of recurrent laryngeal nerve pathology or arytenoid fixation resulting from fibrosis or atresia of the posterior glottis. In cases of severe laryngomalacia ( Fig. 13-2 ), ML&B can be used to perform cold surgical or laser supraglottoplasty.
Laryngeal webs, cysts, clefts, and laryngoceles are rare congenital anomalies of the larynx that are difficult to visualize on bedside examination. Laryngeal webs are caused by incomplete recanalization of the laryngotracheal tube during the third month of gestation. Laryngoceles are air-filled dilations of the laryngeal saccule that communicate with the laryngeal ventricle, whereas saccular cysts are fluid-filled dilations of the saccule that do not communicate with the airway. Rigid microlaryngoscopy is also used in the diagnosis and treatment of submucosal lesions, such as venolymphatic malformations. Laryngeal and subglottic infantile hemangiomas may cause progressive, biphasic stridor within the first few months of life. They are sometimes associated with cutaneous hemangiomas and often respond well to chronic propranolol therapy, which is used until the growth phase has subsided and involution has occurred.
Laryngeal clefts are rare anomalies that present with stridor and aspiration. A type I laryngeal cleft is confined to the interarytenoid space, a type II cleft extends through part of the cricoid, a type III cleft extends completely through the cricoid, and a type IV cleft extends beyond the cricoid into the trachea.
When the etiology of noisy breathing in the neonate is not apparent based on NPL examination, it is important to visualize the subglottis with ML&B. Subglottic cysts can cause obstruction of the subglottic airway, resulting in stridor. They are almost always associated with a history of endotracheal intubation and often occur in association with subglottic stenosis ( Fig. 13-3 ). Subglottic stenosis is an important cause of stridor in neonates. In most cases it is acquired, but 5% of cases represent congenital forms of this condition. It should be considered in the differential diagnosis when an age-appropriate endotracheal tube cannot be passed during attempts at intubation. Acquired subglottic stenosis results when subglottic edema associated with the presence of an endotracheal tube impairs capillary perfusion of the subglottic mucosa. Necrosis and chondritis ensue and a fibrocartilaginous scar is formed. Risks are increased with larger endotracheal tubes, prolonged intubation, repeated or traumatic intubations, and infection.
The severity of subglottic stenosis is graded using the Cotton-Myer grading system. A stenosis is grade 1 when 0% to 50% of the lumen is obstructed, grade 2 with 50% to 75% obstruction, grade 3 with 75% to 99% obstruction, and grade 4 when the airway lumen is completely obstructed. Based upon the etiology, grade, and thickness of obstruction, various surgical techniques have been developed for the management of subglottic stenosis including laryngotracheal reconstruction with costal cartilage grafting, cricoid split, and cricotracheal resection. In neonates with severe stenosis, a tracheostomy may be required until definitive surgical management can be performed.
Another important cause of stridor in the neonate is congenital tracheal stenosis due to complete cartilaginous tracheal rings. In these infants, the membranous posterior wall of the trachea is replaced by cartilage. The number of rings varies, and the diameter tends to narrow with each subsequent ring, giving a funneled appearance on radiographic images. The airway of a neonate with complete tracheal rings is tenuous and must be treated with caution because of the risk of obstructive mucous plugs and limited options for endotracheal intubation. Irritation of the mucosa in the stenotic segment by rigid bronchoscopy or an endotracheal tube can result in airway edema and exacerbate airflow obstruction in the trachea.
Tracheoesophageal fistulae (TEF) are well visualized with rigid bronchoscopy. A TEF results from failed closure of the tracheoesophageal septum during embryologic development. There are five types of TEF, the most common of which is associated with proximal esophageal atresia and the distal esophagus arising from the lower trachea or carina. Some degree of associated tracheomalacia is inherent to this disorder.
Risks, Contraindications, and Limitations
The requirement of general anesthesia for ML&B make it a higher risk procedure than NPL; however, the risk of serious complications remains low. Common adverse events include cough, oxyhemoglobin desaturation, hypoventilation, and laryngospasm. Bleeding and damage to the lips, gums, and maxillary alveolus are uncommon when appropriate precautions are taken.
Equipment
The procedure requires a light source; a rigid laryngoscope, telescope, or microscope; and a suspension arm if interventions are to be performed. Laryngoscopes are available in a variety of lengths, diameters, and angles. Selection is based upon surgeon preference, indications for the procedure, and which interventions need to be performed ( Figs. 13-4 and 13-5 ).
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