There are distinct differences in the pediatric and adult airway, including the fact that the infant airway is situated higher in the neck (between the second and fourth cervical vertebrae) than in the adult.
Principles related to Poiseuille’s law state that a narrow airway lumen results in more turbulent air flow and higher resistance to air movement creating a small lesion, which may not even be symptomatic in an adult, that causes significant respiratory compromise in a pediatric patient.
Symptoms of respiratory distress are closely associated with issues of the digestive system and may present in conjunction with aspiration and failure to thrive.
Choanal atresia presents as a mixed bony/membranous atresia in 70% of patients and as a pure bony atresia in 30%, with a 2:1 predominance for females.
Laryngomalacia is the most common congenital anomaly of the larynx, characterized by excess supraglottic tissue, shortened aryepiglottic folds, and low laryngeal tone. It is also the most common cause of stridor in infants.
Propanolol has become a mainstay in the medical therapy for children with subglottic hemangioma.
Laryngotracheal stenosis or subglottic stenosis can present as a congenital airway obstruction and occurs most commonly at the level of the cricoid cartilage, which is a complete circumferential ring of cartilage. Characteristics and size of endotracheal tubes may contribute to scar tissue in the subglottis with subsequent stenosis.
Diseases leading to compromise of the airway are a frequent cause of morbidity and mortality in pediatric patients. The upper airway in particular plays a critical role in basic functions, such as feeding, breathing, and voicing. Pathology related to the upper airway often affects all three of these processes. Furthermore, airway compromise is the most frequent cause of cardiac arrest in pediatric patients. Respiratory failure can be caused by obstruction, mechanical impairment of ventilation, neuromuscular failure, and failure of oxygen delivery to the tissue. Specific diseases of the upper airway leading to obstruction are discussed.
Anatomy and physiology
Distinct differences in the pediatric airway and adult airway exist that may predispose patients to acute airway obstruction. The upper airway is composed of multiple subsites, including the nasal cavity, nasopharynx, oral cavity, oropharynx, and larynx. The larynx can be divided into three separate subsites. The supraglottis includes the epiglottis, arytenoid cartilages, aryepiglottic folds, and a portion of the false vocal cords. The glottis is composed mainly of the true vocal cords, which are the main mechanism of phonation. The subglottis consists of the area immediately below the true vocal cords, bounded by the cricoid cartilage.
The infant larynx is situated higher in the neck than that of an adult, between the second and fourth cervical vertebrae. This initial more cephalad position brings the epiglottis into contact with the soft palate, making the neonate an obligate nasal breather for the first months of life. As the child matures to an adult, the larynx descends to the level of the seventh cervical vertebra.
Traditional teaching has been that the larynx and trachea differ greatly between young children and adults, with the immature airway having a conical shape and the mature airway a cylindrical shape. However, observations from modern imaging techniques, including bronchoscopy, computed tomography (CT), and magnetic resonance imaging (MRI), provide evidence that contradicts previous dogma. In fact, the immature larynx is roughly cylindrical and similar to that of the adult. The glottis of a newborn measures 7 mm in the anteroposterior dimension and 4 mm in the transverse dimension. The subglottis typically measures between 3 and 4 mm. Reduction of the subglottic lumen due to structural dysfunction or edema of even 1 mm can reduce the lumen by approximately 30%. Poiseuille’s law stipulates that laminar flow of gas through a tube is inversely proportional to the fourth power of the radius of the lumen:
where R is the resistance to gas flow, l is the length of the tube, n is the viscosity of the gas, and r is the radius. In translation, a narrow airway lumen results in more turbulent flow and higher resistance to air movement. Because of this, a small lesion, which may not even be symptomatic in an adult, may cause significant respiratory compromise in a pediatric patient.
Diagnosis and management
Common symptoms of respiratory distress include increased work of breathing, tachypnea, nasal flaring, use of accessory muscles, and cyanosis. They are often closely associated with issues of the digestive system and present in conjunction with aspiration or failure to thrive. Symptoms may vary based on the location and severity of the obstruction. Quality of breathing and of symptoms such as stridor may provide clues that can aid in expedient diagnosis. Nasopharyngeal and oropharyngeal obstruction produces stertor, a low-pitched snuffling sound, or snoring. Collapse of supraglottic or glottic structures due to the negative pressure created during inspiration produces inspiratory stridor. Intrathoracic obstruction or collapse causes expiratory stridor. Fixed obstructions, such as subglottic stenosis or tracheal lesions, produce biphasic stridor.
When airway obstruction is suspected, careful and gentle examination of the head, neck, and thorax should be performed. Care should be taken to disturb the patient as little as possible, as airway obstruction often worsens when a patient becomes agitated. Humidified oxygen should be administered via nasal cannula or facemask. If these devices frighten the child, it may be helpful to have the parent hold the child and subsequently hold the oxygen delivery device in proximity to them. Pulse oximetry should be placed if the child will tolerate it, but more invasive measures, such as arterial blood gas sampling, should be avoided unless the obstruction appears to be severe.
The initial evaluation should be accomplished expeditiously with the goal of making decisions about the management and need for further evaluation of airway compromise. In the stable patient, further testing—such as neck and chest radiograph, CT, or flexible fiberoptic laryngoscopy performed by an otolaryngologist—may be pursued. Those with an unstable airway must have it expertly secured.
Congenital malformations of the upper airway
Congenital malformations of the upper airway, while uncommon overall, can be a common cause of pediatric airway obstruction. Many of these become evident in the delivery room, but some may not become evident until the child is older. They may occur as isolated anomalies or in conjunction with a syndrome.
Choanal atresia is manifested by complete closure of the posterior nasal apertures (choanae). Its incidence is estimated to be between 1 in every 5000 to 9000 live births. The obstruction almost always has a bony component but may have a membranous component as well. Current reports estimate a mixed bony/membranous atresia in 70% and pure bony at 30%. There is a 2:1 predominance in females, with unilateral atresia occurring more commonly than bilateral atresia. , Unilateral choanal atresia is often seen in isolated cases, while bilateral choanal atresia frequently occurs in the presence of other congenital defects ( Fig. 47.1 ). CHARGE syndrome ( c oloboma, h eart defects, a tresia choanae [also known as choanal atresia], growth r etardation, g enital abnormalities, and e ar abnormalities) has a particularly strong correlation, and accounts for 25% of all patients with choanal stenosis or atresia. ,
Unilateral choanal atresia may be missed at the time of delivery, but bilateral choanal atresia often results in respiratory distress shortly after birth. As neonates are obligatory nasal breathers, no airflow will be present at rest with a closed mouth and respiratory distress will ensue. When the neonate cries, respiratory status will temporarily improve. An oral airway or McGovern nipple may be used as a temporary measure until diagnosis is established. Some advocate passing a thin, flexible catheter through the naris to confirm choanal atresia. While this may help confirm diagnosis, the provider must be aware that even minor trauma can cause edema, leading to complete occlusion of the nasal airway in patients with stenosis or incomplete obstructions. Definitive diagnosis is achieved with a CT scan or direct visualization using an endoscope. CT scanning is widely considered the standard as it not only confirms choanal atresia but also assists with surgical planning. , Surgery is indicated for all cases of bilateral atresia and in cases of unilateral atresia or stenosis when the patient is symptomatic ( Fig. 47.2 ). Infants with bilateral atresia generally have surgery soon after birth, whereas infants with unilateral atresia typically have surgery after age 2 years.
Laryngomalacia is the most common congenital anomaly of the larynx. It is characterized by excess supraglottic tissue, shortened aryepiglottic folds, and low laryngeal tone. Laryngomalacia is also the most common cause of stridor in infants, accounting for 45% to 75% of all cases. The stridor is inspiratory in nature and worsens with feeding, crying, agitation, and supine position. Noise occurs due to the collapse of supraglottic structures inward (toward the glottis) from negative intrathoracic pressure generated during inspiration ( Fig. 47.3 ). Infants with laryngomalacia often also have difficulty coordinating the suck-and-swallow breath sequence needed for feeding as a result of their airway obstruction. This subsequently leads to feeding issues and, in severe cases, failure to thrive. Additionally, the increased intrathoracic pressure generated to bypass the obstruction from laryngomalacia leads to increased incidence of gastroesophageal reflux disease (GERD). GERD is present in 65% to 100% of infants with laryngomalacia, and leads to a cycle of edema, worsening obstruction, and further reflux. , Airway obstruction from laryngomalacia also leads to obstructive sleep apnea in 27% of patients with this condition.
The majority (80%) of cases of laryngomalacia are mild and self-limited and will resolve on their own within 12 to 24 months. These patients are generally managed with conservative measures and medical therapy for reflux. For patients with severe laryngomalacia, surgical intervention with supraglottoplasty is necessary. , Without treatment, patients with severe laryngomalacia are at risk of chronic hypoxia, pulmonary hypertension, and cor pulmonale .
Laryngeal webs and atresia
Congenital laryngeal webs most often occur at the level of the glottis ( Fig. 47.4 ). The fibrous band generally is located between the anterior third of the vocal cords but may extend posteriorly and inferiorly into the subglottis. This malformation occurs due to incomplete recanalization of the primitive larynx during embryogenesis. It may also occur later in childhood as a result of chronic trauma. Symptoms include a weak, husky, or absent cry; biphasic stridor; dyspnea; and episodic cyanosis. , If greater than 75% of the glottis is involved, the infant may be aphonic and develop respiratory distress soon after birth. Diagnosis is confirmed with laryngoscopy. Treatment for symptomatic patients is largely surgical and dependent on the degree of obstruction.
Complete webs (laryngeal atresia) are extremely rare and incompatible with life unless diagnosed prenatally. They can be visualized on prenatal ultrasound as a constellation of symptoms called congenital high airway obstruction syndrome (CHAOS), which include hyperechoic lungs; flattened or inverted diaphragm; fluid-filled, dilated airway; and polyhydramnios. If identified before birth, an ex utero intrapartum treatment (EXIT) procedure and tracheostomy can be planned, with later repair or reconstruction of the malformed larynx.
Cysts may occur in any location in the larynx but are frequently seen in the saccule, which lies between the false vocal folds and true vocal cords. When filled with air and connected to the laryngeal lumen, these cysts are called laryngoceles . When located in the submucosa and separated from the lumen, they are termed saccular cysts . Congenital laryngeal cysts are rare, occurring in only one to two patients per every 100,000 live births. They may not be noted until later in life, when they become infected or grow to protrude into the airway or lateral neck ( Fig. 47.5 ). Laryngoceles may become dilated over time with repeated increases in intralaryngeal pressure, such as from playing wind instruments. Either type of cyst may manifest as respiratory distress if airway obstruction is severe, but more commonly present with stridor, dyspnea, hoarseness, or dysphagia. Diagnosis is made with imaging or flexible laryngoscopy. Saccular cysts do not fluctuate, but laryngoceles can be challenging to diagnose if the cyst is not filled with air at the time of examination. Treatment is surgical and can range from needle aspiration to marsupialization to complete excision. There is a high risk of recurrence if not treated aggressively; thus, some practitioners advocate for upfront endoscopic or open resection.
Laryngeal clefts are characterized by midline tissue deficiency in the separation of the larynx and trachea from the esophagus. Their incidence is 1 in 10,000 to 20,000 births, and they comprise approximately 1.5% of all pediatric laryngeal pathologies. There is a high risk of comorbidities (56%), most commonly tracheoesophageal fistula (20%–27%). The most common grading scale is the Benjamin and Inglis classification, which groups the cleft by type based on inferior extent ( Fig. 47.6 ). Symptomatology varies widely based on the type of cleft. Type I clefts may be asymptomatic or have mild symptoms, such as cough, dysphagia, hoarseness, or hypersecretion. Types II and III clefts have more severe symptoms and are common, characterized by aspiration and recurrent pneumonia. Type IV clefts present with significant respiratory distress and have a poor prognosis. The gold standard for diagnosis is operative laryngoscopy and bronchoscopy. This is often done in conjunction with an aerodigestive team comprising otolaryngologists, pulmonologists, and gastroenterologists, as patients with laryngeal clefts frequently have multisystem complaints. Treatment varies based on the severity of symptoms and severity of the tissue defect. Minor laryngeal clefts may be treated with feeding and gastroesophageal reflux therapy, while more severe clefts may necessitate injection of bulking agent, endoscopic suture repair, or open laryngeal reconstruction.
Vocal cord paralysis
Vocal cord paralysis (VCP) is the second most common cause of stridor in the neonate, second only to laryngomalacia. Unilateral VCP and bilateral VCP occur with similar frequencies, although they may have different etiologies. Potential causes are neurologic, infectious, trauma, iatrogenic, or idiopathic. Chemotherapeutic agents, such as vincristine, are also a rising cause of VCP. Flexible fiberoptic laryngoscopy should be carried out in any patient suspected of having VCP to establish the diagnosis.
Bilateral VCP in pediatric patients is most often from a congenital cause, generally related to neurologic conditions. , There is a strong correlation between VCP and Arnold-Chiari malformation, in which the contents of the posterior fossa herniate and put pressure on the vagus nerve at the skull base either directly or secondarily from hydrocephalus. , VCP is also seen in cases of vertex delivery where forceps are used, which can put pressure on the recurrent laryngeal nerves. , The most common presenting symptom for bilateral VCP is inspiratory stridor, which may be accompanied by dyspnea. The voice may be unaffected, as the vocal cords typically rest in the paramedian position.
Unilateral VCP, while it may be congenital, is more commonly iatrogenic. Cardiothoracic surgery is the most common cause—specifically, surgery involving the aortic arch or to ligate a patent ductus arteriosus. This normally results in a left-sided paralysis. Other causes include tracheoesophageal fistula repair, neurologic disease, trauma, and viral infection. , Stridor is less common in patients with unilateral VCP. They more often present with a weak, breathy cry, and with feeding issues secondary to aspiration.
Treatment of vocal cord paralysis in the critical care setting is primarily supportive. Airway support may include high-flow nasal oxygen or continuous positive airway pressure/biphasic positive airway pressure (CPAP/BiPAP). Vocal cord paralysis in infants often resolves spontaneously within 6 to 18 months but is unlikely to improve if no return of function has manifested after 2 years. While patients with unilateral VCP can often be temporized with speech therapy or injections, 60% of patients with bilateral VCP require tracheostomy. If a specific lesion may be addressed medically or surgically (such as occipital decompression in Arnold-Chiari malformation), such therapy should be undertaken without delay.
Vascular compression of the trachea
Airway obstruction can occur due to the presence of an abnormal vascular structure compressing the trachea ( Fig. 47.7 ). These anomalies result from disruption of the fourth or sixth branchial arch during embryogenesis. An aberrant innominate artery is the most common cause for congenital vascular compression. The abnormal artery will originate more distally (leftward), and cause compression as it travels anterior to the trachea (rightward). An aberrant pulmonary artery, also called pulmonary artery sling , causes posterior tracheal compression. This occurs when the left pulmonary artery arises from the right pulmonary artery and passes between the trachea and esophagus as it courses toward the left lung. Aortic arch anomalies, such as a double aortic arch, may cause circumferential vascular compression. Vascular anomalies may result in airway issues such as stridor, cough, and apneas as well as esophageal symptoms such as dysphagia. Alternatively, patients may be relatively symptom free but suffer from recurrent lobar atelectasis, wheezing, or pulmonary infections. Diagnostic testing includes chest radiographs, esophagram, contrasted CT or MRI, and direct laryngoscopy and bronchoscopy ( Fig. 47.8 ). CT and MRI have become the modalities of choice, as they are noninvasive and effective at showing the complex three-dimensional cardiovascular anatomy and morphology. Treatment involves surgical correction of the vascular anomaly in severe cases.
Neoplasms of upper airway disease
Tumors of the airway are rare in children. When they do occur, they are more often benign. They present with typical symptoms of airway obstruction but may be missed initially as more common infectious and inflammatory causes are ruled out. If left undiagnosed or untreated, life-threatening airway obstruction may ensue.
Laryngeal papillomas, in the setting of recurrent respiratory papillomatosis (RRP), are the most common benign tumors of the larynx in children. They may occur anywhere in the airway, but the larynx is the most common location. RRP has a bimodal pattern, occurring either in early childhood or in adulthood. Its presentation in children is more aggressive and persistent. Therefore, it is sometimes referred to separately as juvenile recurrent respiratory papillomatosis (JRRP). Human papilloma virus (HPV) is a well-established cause of RRP, with types HPV-6 and HPV-11 being most prevalent. These subtypes are considered low risk compared with other HPV subtypes, such as HPV-16 and HPV-18, which are commonly associated with oropharyngeal squamous cell carcinoma. Malignant transformation of RRP is less than 1%.
Transmission of HPV occurs from mother to child either in utero or at birth. A rise in JRRP has been seen with increasing prevalence of HPV cervical infections. Incidence in the United States is estimated at 4 cases per every 100,000 births. JRRP generally does not manifest immediately but has a more indolent course. It is most commonly diagnosed between 2 to 4 years of age. Voice change is the most common presenting symptom, present in 90% of cases. Diagnosis is typically made with laryngoscopy. Treatment is surgical excision, often using a laser, and patients typically require serial operations over their lifetime ( Fig. 47.9 ). Medical therapies, such as interferon-α and cidofovir, have been proposed as adjuvants to surgery.
Hemangiomas are the most common tumor of the head and neck in pediatric patients. These lesions grow rapidly within the first year of life, and involute slowly over many years. Subglottic hemangiomas (SGHs) are seen almost exclusively in infants but are not often apparent at birth. The proliferation phase begins at 1 to 2 months of age, and 85% are diagnosed before 6 months. Symptoms of SGH include respiratory distress, biphasic stridor, and feeding difficulties as the infant struggles to feed and breathe simultaneously. SGHs are also frequently misdiagnosed as croup, as they may have a similar barking cough, and are improved with steroids and breathing treatments (which temporarily decrease the size of the hemangioma). A key way to differentiate between them is lack of fever and rhinorrhea. Symptoms of SGH will also recur shortly after treatment; therefore recurrent croup in the neonatal period should always raise suspicion for SGH. Diagnosis is made with direct laryngoscopy and bronchoscopy, typically in the operating room as anesthesia is needed to allow adequate visualization of the subglottis.
Cutaneous hemangiomas are commonly associated with SGH, and occur simultaneously in 50% of cases. The association is particularly strong in patients with a “beard” distribution (preauricular, chin anterior neck, lower lip) of cutaneous hemangiomas, although its biological basis is not well understood. Both subglottic and facial hemangiomas can be seen in PHACES syndrome, a constellation of p osterior fossa malformation, segmental facial h emangiomas, a rterial anomalies, c ardiac defects, e ye anomalies, and s ternal defects. Patients with SGHs and cutaneous hemangiomas should be screened with an MRI of the brain to rule this intracranial posterior fossa malformations or arterial malformations, which may be life-threatening.
Treatment is dependent on symptoms and on the severity of the SGH. Small lesions may be observed. If left untreated, 50% will achieve complete resolution by age 5 years, and 70% by age 7 years. Reflux management should be considered in these patients to prevent further airway edema. Propranolol has become another mainstay in medical therapy of hemangiomas and can yield significant reductions in size. Surgical therapy, often including use of a CO 2 laser, is reserved for large SGHs causing airway compromise.
Other tumors of the larynx and upper airway
While rare, a variety of epithelial, mesenchymal, and hematopoietic laryngeal tumors have been reported in pediatric patients. Mesenchymal tumors, such as rhabdomyosarcoma, are the most common among these, making up nearly two-thirds of cases. This is in contrast to adult laryngeal malignancies, of which epithelial tumors (squamous cell carcinoma, in particular) are significantly more common. Early identification and subsequent treatment planning are essential for these tumors. Depending on the type of malignancy, therapy consists of surgery, chemotherapy, radiation, or a combination of these modalities.
A variety of infectious processes may affect the pediatric airway. Poiseuille’s law dictates that airway compromise from the swelling that accompanies an infection is greater in infants and young children than in adults. A small reduction in the caliber of a child’s airway may progress rapidly to significant respiratory distress and potentially cause a life-threatening reduction of airflow.
Laryngotracheobronchitis (croup) is the most common cause of infectious airway obstruction, affecting approximately 3% of children in the United States each year. Parainfluenza virus is the most common agent, with coronavirus and rhinovirus constituting the majority of the remainder of infections. Croup is a seasonal illness, occurring predominantly during fall and winter, though sporadic cases can be seen year round. Children from age 6 months to 3 years are most commonly affected. Prior to respiratory compromise, a prodrome of upper respiratory symptoms and a barky cough (described as sounding like the bark of a seal) are often observed. Subsequent swelling of the mucosa in the subglottis leads to stridor and respiratory distress. Various scales have been devised to quantify the severity of stridor and to document the progression of the illness and its response to therapy. One of the most commonly used scales is the Westley scale ( Table 47.1 ), which has been validated. ,