Croup

Croup illnesses can be divided into two categories: (1) acute laryngotracheobronchitis (croup) and (2) spasmodic croup. Diphtheria can be considered a croup illness but is now rare because of vaccinations. Croup illnesses are all characterized by infection and obstruction of the upper airways.¹

Croup is an acute laryngotracheobronchitis and most commonly occurs in children from 6 months to 3 years of age, with peak incidence at 2 years of age.² In 85% of cases, croup is caused by a virus, most commonly parainfluenza; however, other viruses such as influenza A virus, respiratory syncytial virus (RSV), rhinovirus, adenovirus, and rubella virus (measles) as well as the atypical bacterium Mycoplasma pneumoniae has been associated with causation. The incidence of croup is highest in late autumn and winter, corresponding to the parainfluenza and RSV seasons, respectively. Croup is more common in boys than girls. In a significant portion of affected children, croup is a recurrent problem during childhood, and there is a family history of croup in about 15% of cases. Spasmodic croup is characterized by similar hoarseness, barking cough, and stridor, but is of sudden onset, usually at night and without viral prodrome. It often resolves as quickly as it develops and usually occurs in older children. The etiology is unknown although association with viruses, allergies, asthma, and gastroesophageal reflux disease (GERD) is being investigated.³

Pathophysiology

The pathophysiology of viral croup is caused primarily by subglottic edema from the infection. The mucous membranes of the larynx are tightly adherent to the underlying cartilage, whereas those of the subglottic space are looser and thus allow accumulation of mucosal and submucosal edema (Figure 36-6). Furthermore, the cricoid cartilage is structurally the narrowest point of the airway, making edema in this area critical. As illustrated in Figure 36-7, increased resistance to airflow leads to increased work of breathing, which generates more negative intrathoracic pressure, which in turn may exacerbate dynamic collapse of the upper airway.

Clinical Manifestations

Typically there is a prodrome of rhinorrhea, sore throat, and low-grade fever for a few days. The child then develops the characteristic harsh (seal-like) barking cough, hoarse voice, and inspiratory stridor. Most cases are mild and resolve spontaneously after several more days. Occasionally, however, UAO becomes severe and requires urgent management.

Evaluation and Treatment

The degree of symptoms determines the level of treatment. Most children have a barking cough and viral symptoms and may need no specific treatment. However, the presence of stridor (especially at rest), retractions, or agitation suggests a sicker child. The tool most often used for estimating croup severity is the Westley croup score, which provides a cumulative score for the degree of stridor, retractions, air entry, cyanosis, dyspnea, and level of consciousness in the child.⁴

Severity also is classified as mild, moderate, and severe. Most children with croup require no treatment. Inhalation of humidified air does not improve symptoms in mild to moderate croup.⁵ Glucocorticoids, either injected or oral (dexamethasone) or nebulized (budesonide), have been shown to improve symptoms within 6 hours. Less sleep is lost by children, less stress is experienced by parents, and fewer children have a need for return healthcare visits or hospitalization when corticosteroids are used.⁶ The use of nebulized racemic epinephrine improves outcomes with moderate to severe croup.^2,7 Epinephrine stimulates α- and β-adrenergic receptors and is thought to decrease airway secretions and mucosal edema. It is a temporizing measure until concomitantly given corticosteroids begin to take effect. Thus children who are given nebulized epinephrine should be closely observed for 2 to 3 hours to ensure that they will remain stable. Oxygen also should be administered. Heliox (helium-oxygen mixture of 80:20 or 70:30) may be used for severe cases of croup, although there is lack of scientific evidence to establish use in routine clinical practice.⁸

Acute Epiglottitis

Historically, acute epiglottitis was caused by Haemophilus influenzae type B (Hib). Since the advent of Hib immunization, the overall incidence of acute epiglottitis in children has decreased significantly, although Hib still accounts for approximately 25% of the cases seen in children. Infants less than 1 year of age are at greater risk.⁹ Current pediatric cases usually represent Hib vaccine failures or are caused by alternative pathogens, such as groups A, B, C, F, and G streptococci, Streptococcus pneumoniae, Candida species, Staphylococcus aureus, and viral pathogens. Thermal injuries, trauma, and posttransplant lymphoproliferative disorder also have been reported as causes of epiglottitis.¹⁰

Pathophysiology

The epiglottis arises from the posterior tongue base and covers the laryngeal inlet during swallowing. It has a rich blood and lymphatic circulation. Bacterial invasion of the mucosa with associated inflammation leads to the rapid development of edema causing severe, life-threatening obstruction of the upper airway.¹⁰

Clinical Manifestations

In the classic form of the disease, a child between 2 and 6 years of age suddenly develops high fever, irritability, sore throat, a “hot potato voice,” inspiratory stridor, and severe respiratory distress. The child appears ill and classically will adopt a forward-leaning position (tripod position) with drooling and dysphagia (inability to swallow). Examination of the throat may trigger laryngospasm and cause respiratory collapse. Death may occur in a few hours. Pneumonia, cervical lymph node inflammation, otitis, and, rarely, meningitis or septic arthritis may occur during the course of epiglottitis.

Evaluation and Treatment

Acute epiglottitis is a life-threatening emergency. The essentials are early recognition, avoidance of disturbing the child (which could worsen the obstruction), and securing the airway. Examination of the throat should not be attempted because it may trigger laryngospasm and cause respiratory collapse. Tracheal intubation should be accomplished by the most experienced personnel (usually an anesthesiologist and/or otolaryngologist) using fiberoptic laryngoscopy. Subsequent culture of the airway is obtained and intravenous broad-spectrum antibiotics are administered promptly. Therapy is reevaluated after culture results return. Corticosteroids also are generally used in treatment regimens although there are no published randomized trials to support this practice.10–12 Despite the severe presentation of epiglottitis, resolution with treatment is usually rapid, with intubation rarely needed for more than a couple of days. When Hib epiglottitis is diagnosed, the American Academy of Pediatrics (AAP) recommends that postexposure prophylaxis with rifampin be administered to household contacts (specific to certain ages of children present).¹² When caused by microorganisms other than H. influenzae, as is now the usual situation, epiglottitis may present in ages outside the typical range and with more gradual rather than fulminant onset, thus making diagnosis less obvious. Such cases also may respond more slowly to treatment.

Tonsillar Infections

Tonsillar infections (tonsillitis) are occasionally severe enough to cause UAO.¹³ As with other infections of the upper airway, the incidence of tonsillitis secondary to group A beta-hemolytic Streptococci (GABHS) and methicillin-resistant S. aureus (MRSA) has risen notably in the past 15 years.¹⁴ Significant swelling of the tonsils and pharynx occurs, and a tenacious membrane may cover the mucosa. UAO because of tonsillitis is a well-known complication of infectious mononucleosis, especially in a young child. The development of UAO in tonsillar infections requires the use of appropriately selected antibiotics and may require the use of corticosteroids, especially in the case of mononucleosis.¹⁵ Some children with recurrent tonsillitis benefit from tonsillectomy.

Peritonsillar abscess is usually unilateral and is most often a complication of acute tonsillitis.¹⁶ The most common causative microorganism is GABHS. Children have fever, sore throat, dysphagia, trismus, pooling of saliva, and muffled voice. Peritonsillar bulging (Figure 36-8) and cervical adenopathy on the same side are usually visible. The abscess must be drained and the child given antibiotics.¹⁷ Death can occur from spontaneous abscess rupture with aspiration or airway obstruction.¹⁸

Bacterial Tracheitis

Bacterial tracheitis is the most common potentially life-threatening upper airway infection in children. It is most often caused by Staphylococcus aureus (S. aureus) (including methicillin-resistant [MRSA] strains), H. influenzae, group A beta-hemolytic Streptococcus (GABHS [Streptococcus pyogenes]), or Moraxella catarrhalis.¹⁹ It accounts for 5% to 14% of UAOs in children requiring intensive care.²⁰ A virus or a fungus is more likely to be seen as the source of tracheitis in immunocompromised children.²¹ Treatment of viral croup with corticosteroids has increased the risk for serious bacterial tracheitis (especially by GABHS), resulting in death rates between 18% and 40%.²⁰ The presence of airway edema and copious purulent secretions leads to airway obstruction that can be worsened by the formation of a tracheal pseudomembrane and mucosal sloughing. Increased morbidity can occur because of respiratory and cardiopulmonary arrest, respiratory failure, pneumonia, septic shock, toxic shock syndrome, acute respiratory distress syndrome (ARDS), and multiple organ dysfunction syndrome (MODS). The onset of symptoms may be sudden or may be preceded by a pre-existing viral upper respiratory tract infection or croup. The acute clinical presentation frequently includes tachypnea, stridor, hoarse voice, fever, cough, and/or increased secretions from the mouth and nose. There may be evidence of concurrent infections, such as sinusitis, otitis, pneumonia, or pharyngitis.²² Children with chronic gastroesophageal reflux are more likely to experience difficulty with these types of concurrent infections. Management requires the rapid administration of broad-spectrum intravenous antibiotics. The majority of children with tracheitis require endotracheal intubation in order to prevent airway obstruction. Corticosteroids (parenteral and inhaled) are used to decrease tracheal inflammation. Many children recover adequately to be extubated within 72 to 96 hours.²³

Retropharyngeal Abscess

Retropharyngeal abscess can be caused by aerobic, anaerobic, or polymicrobial infection. A decrease in retropharyngeal abscess has been noted in the past several years that is likely related to the use of corticosteroids in the treatment of influenza and croup. There also has been an increase in GABHS strains associated with this condition, and the emergence of MRSA as the offending microorganism is increasingly noted.²⁴

Retropharyngeal abscess usually occurs more commonly in male children about 4 years of age and as a consequence of either nasopharyngeal infection or penetrating local injury.²⁵ Clinical signs include fever, dysphagia, drooling, stridor, respiratory distress, and stiff neck. This condition requires intravenous antibiotics targeted at the suspected microorganism, and sometimes incision and drainage.²⁶

Laryngomalacia and Tracheomalacia

Laryngomalacia results from abnormally soft laryngeal cartilages and is the most common cause of chronic stridor in infants. Boys are twice as likely as girls to present with symptoms. In laryngomalacia, the epiglottis or arytenoids, or both, fold inward with inspiration, partially covering the glottis (Figure 36-10). The pathophysiology of these abnormalities is still not completely understood. Two primary hypotheses are anatomic or neuromuscular.³⁶ Anatomically there may be foreshortened or tight aryepiglottic folds or there may be redundant soft tissue in the supraglottis.³⁷ The neuromuscular hypothesis suggests that there is an abnormality of the sensorimotor integrative function of the brainstem and peripheral reflexes are responsible for laryngeal tone and airway patency.³⁸ Laryngeal nerve hypertrophy also has been documented.³⁹ Gastroesophageal reflux disease (GERD) and other comorbidities are associated with laryngomalacia.⁴⁰

Typical signs of laryngomalacia include inspiratory stridor beginning in the first days or weeks of life, accentuated with activity, and sometimes with positional changes (worse in supine or head-flexed positions). Feeding difficulties may be noted, but they are usually mild. Cry is normal. Laryngoscopy is used to confirm the diagnosis. Laryngomalacia is usually mild and improves spontaneously over the first year of life as the supralaryngeal cartilage structures stiffen; thus most cases are managed with watchful waiting. A late-onset variant of this disease has been noted in the literature and should be suspected if the following occurs: potential cause of feeding difficulties in toddlers, sleep apnea in children, and exercise intolerance in teenagers.41,42

In tracheomalacia, or tracheobronchomalacia, the tracheobronchial cartilages are flaccid and tend to collapse during the expiratory cycle, causing stridor. This may be classified as primary (idiopathic) or secondary. When malacia is caused by a secondary source, it is usually related to extrinsic compression of the trachea from a vascular malformation (congenital tracheomalacia). Tracheobronchomalacia presents clinically as a spectrum of respiratory illnesses that range from life-threatening conditions to chronic cough and wheeze conditions. In some cases symptoms may be more subtle than in laryngomalacia. Low-pitched inspiratory stridor may be a sign of malacia of the upper trachea or centrally located, single-pitch (monophonic) wheeze may be present in malacia of the middle to distal trachea. Tracheomalacia can be suspected clinically and confirmed by bronchoscopy. Depending on the type and severity of the lesion, surgical approaches for repair may be indicated.⁴³

Vocal Cord Paralysis

Vocal cord paralysis is second to laryngomalacias as a cause of stridor and is a relatively uncommon congenital disorder. The vocal cords should move apart to facilitate inspiration and move together to facilitate vocalization. Paralysis of one or both vocal cords may affect breathing, swallowing, and speech. The etiology of the congenital abnormality is unclear but may be caused by immaturity of the vagus nerve or brainstem, or both. Iatrogenic injury is frequently cited as the major secondary cause of vocal cord paralysis, such as surgical trauma to the recurrent laryngeal nerve during cardiac surgery. Other secondary causes include Arnold-Chiari malformation (the region of the brainstem in which the nucleus ambiguus acts as the “relay station” for laryngeal function), cerebral palsy, hydrocephalus, myelomeningocele, spina bifida, or hypoxia.⁴⁴ Other associations include infectious and neoplastic causes, trauma, and inflammatory conditions.⁴⁵ In older children and adolescents, exercise has been known to precipitate vocal cord dysfunction (VCD).⁴⁶

Clinical findings of vocal cord paralysis in children less than 1 year include dysphonia, glottic incompetence, GERD, and stridor.⁴⁵ It sometimes resolves spontaneously (most often during the first year of life) or with correction of the underlying problem. Flexible laryngoscopy and chest x-ray are common evaluative tools that may help determine the cause. In some individuals, VCD may be misdiagnosed as asthma.⁴⁷ Medical therapy may include use of corticosteroids, proton pump inhibitors, and speech therapy. Recurrent pulmonary infections secondary to aspiration may occur and require treatment until the cords are repaired.⁴⁸ Severe cases may necessitate endotracheal intubation and tracheostomy. Tracheostomy may be used until the vocal cords are surgically repaired or can be used as a permanent measure for bilateral vocal cord paralysis.⁴⁸

Subglottic Stenosis

Congenital subglottic stenosis is the third most common laryngeal anomaly and is defined as a subglottic airway diameter of less than 4 mm at the cricoid region in a full-term infant, and less than 3 mm in a premature infant.⁴⁸ Incomplete recanalization of the laryngotracheal tube during the third month of gestation results in this defect. Subglottic stenosis also is associated with eosinophilic esophagitis, Wegener granulomatosis, and neurofibromatosis.^49–51 Traumatic injury to the upper airway with development of subglottic stenosis is a well-described complication of endotracheal intubation.⁵² Factors that contribute to subglottic stenosis include utilization of long-term assisted ventilation, use of an endotracheal tube that is too large, excessive movement of the tube, and susceptibility of the individual.⁵³ Neonates can tolerate long periods of endotracheal intubation; the overall rate of symptomatic subglottic stenosis in neonates is 0.2%.⁵³ The occurrence of subglottic stenosis can be minimized by ensuring that the tube size allows a small air leak during inspiration (at a peak inspiratory force of approximately 25 mmHg) and that the tube is securely taped. Sedation is generally required to reduce head movement for children who are intubated. Because of the rapid growth of the lumen of the trachea and cricoid cartilage in the first year (which triples in size), infants may outgrow the obstruction, particularly if mild or moderate.⁵⁴ Serial balloon dilation can be effective.⁵⁵ For severe subglottic stenosis, laryngotracheal reconstruction (LTR) along with cricotracheal resection and thyrotracheal anastomosis may be required.⁵⁶

Other Congenital Malformations

Congenital malformations of the upper airways, trachea, and bronchial tree are rare and cause airway obstruction. Lesions include coanal atresia; laryngeal atresias, webs, cysts, clefts, and subglottic hemangiomas; and tracheal stenosis. Coanal atresia can be unilateral or bilateral and causes lack of patency of the nasal cavity within the nasopharynx. Bilateral coanal atresia can be life threatening in newborns because they are obligate nasal breathers.⁵⁷ Laryngeal atresias and webs are caused by failure of the larynx to recanalize during embryogenesis. Most of these disorders are in the area of the glottis with extension into the subglottis.⁴⁸ Tracheal stenosis is a rare malformation characterized by inspiratory and expiratory stridor within the first few weeks of birth. It is usually associated with pulmonary, cardiovascular, and gastrointestinal malformations.⁵⁸ Structural abnormalities such as pectus excavatum or abnormalities involving the great vessels also can result in tracheal compression. For example, absent pulmonary valve syndrome dilates the pulmonary artery, which can compress the trachea and bronchi.⁵⁹ Tracheal or bronchial compression results in airway symptoms or feeding difficulties, or both, ranging from dysphagia, recurrent respiratory tract infections, wheezing, and stridor to acute respiratory distress or “dying spells.” Many older children are first thought to have gastroesophageal reflux or asthma as the principal problem. Surgical management is usually required for these conditions, and some infants may require mechanical ventilation while awaiting surgery.⁵⁹

Pathophysiology

The pathophysiology of childhood OSAS is likely to be multifactorial in origin. The most common predisposing factor is adenotonsillar hypertrophy, which causes physical impingement on the nasopharyngeal airway. OSAS often occurs more frequently in overweight or obese children, as well as in those with orthodontic/craniofacial anomalies, neurologic disorders, allergy, asthma, abnormalities in the motor tone of the upper airways (frequently an issue in neurologically impaired children), abnormal arousal mechanisms, and genetic susceptibility.⁶² Recent studies have documented that children with sleep disordered breathing (SDB) have increased inflammation in the upper airway and elevated serum levels of C-reactive protein, particularly in obese children.⁶³ Activation of inflammatory pathways contributes to end-organ injury with cardiovascular and metabolic morbidities.⁶⁴

Clinical Manifestations

Common manifestations of OSAS include snoring and labored breathing, restlessness, and sweating during sleep, which can be continuous or intermittent. There may be episodes of increased respiratory effort, but no audible airflow, often terminated by snorting, gasping, repositioning, or arousal. Affected children are often chronic mouth breathers and have large tonsils. They also may exhibit nocturnal enuresis.⁶⁵ It appears that there also may be a correlation between OSAS and elevated blood pressure similar to adults.⁶⁶ This is further linked to increased body mass index (BMI) and episodes of desaturation and apnea/hypopnea.⁶⁷

OSAS can result in chronic hypoxemia and hypercapnia affecting multiple organ systems. Significant morbidity is associated with OSAS including cognitive problems, neurobehavioral impairment (e.g., inattention, hyperactivity, aggression, conduct problems, attention-deficit/hyperactivity disorder [ADHD]/emotional [mood]), excessive daytime sleepiness, impaired school performance, and poor quality of life.⁶⁸ Left untreated it also can cause cardiovascular disease, particularly left ventricular hypertrophy, and insulin resistance, as well as pulmonary complications (upper and lower respiratory tract infections) and reduced somatic growth.^69–71

Evaluation and Treatment

All parents should be asked if their child exhibits snoring, a symptom that is often not spontaneously reported to a healthcare provider. The history and physical examination are the most effective means of diagnosis. Screening tools and sleep questionnaires may be helpful in evaluating the presence of SDB.⁷² Radiographic images of the upper airway may reveal upper airway narrowing caused by adenoidal hypertrophy, and magnetic resonance imaging (MRI) and acoustic reflectometry may detect reduced upper airway dimensions.⁷³ The most definitive evaluation (“gold standard”) is the polysomnographic sleep study, which documents obstructed breathing and physiologic impairment and may be combined with nocturnal oximetry studies. If obstructive sleep apnea caused by tonsillar enlargement is documented or strongly suspected clinically, children are most often referred for tonsillectomy and adenoidectomy (T&A). For severely affected children who do not respond to T&A or who have different problems, such as obesity that cannot be rapidly remedied, continuous positive airway pressure (CPAP) delivered through a tight-fitting nasal mask may be used during sleep. Treatment is important to prevent associated morbidities. Successful medical or surgical treatment results in improvement in physical, behavioral, and emotional difficulties as well as quality of life.^74–76

Pathophysiology

RDS is caused by surfactant deficiency, which decreases the alveolar surface area available for gas exchange. Surfactant lipoproteins have a detergent-like effect that separates the liquid molecules inside the alveoli, thereby decreasing alveolar surface tension. Without surfactant, alveoli collapse at the end of each exhalation.⁸¹ Surfactant normally is not secreted by the alveolar cells until approximately 20 to 24 weeks of gestation (see Figure 36-1). Premature infants also are born with underdeveloped and small alveoli that are difficult to inflate. Additionally, the alveoli have thick walls and an inadequate capillary blood supply such that gas exchange is significantly impaired. The infant’s chest wall is weak and highly compliant and, thus, the rib cage tends to collapse inward with respiratory effort. The net effect is atelectasis (Figure 36-11), resulting in significant hypoxemia. Atelectasis is difficult for the neonate to overcome because it requires a significant negative inspiratory pressure to open the alveoli with each breath. The increased work of breathing and a decrease in tidal volume cause alveolar hypoventilation and hypercapnia. Hypoxia and hypercapnia cause pulmonary vasoconstriction, which increases intrapulmonary resistance and shunting. Increased pulmonary vascular resistance causes a partial return to fetal circulation, with right-to-left shunting of blood through the ductus arteriosus and foramen ovale further compromising pulmonary perfusion. There is decreased surfactant production with inadequate pulmonary perfusion and alveolar ventilation.

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