Evaluation of Stridor and Wheezing

LAUREN D. HOLINGER, MD

aSpring 1998

FOR MORE THAN  two decades, I have had the opportunity to evaluate infants and children referred to Children's with symptoms of upper airway obstruction. Parents use a variety of interesting, colorful, sometimes misleading descriptive terms to describe their offspring's acoustic affliction: "noisy breathing," "wheezing," "congestion," "junky," and "sounds like he swallowed a washing machine" are a few. In this brief article, I offer a framework that helps to conceptualize the problem. This approach is primarily based upon hard data from a two-year period in which I evaluated 219 consecutive patients referred with the primary symptom of stridor.¹

Stridor is the audible symptom produced by the rapid, turbulent flow of air through a narrowed segment of the respiratory tract, more specifically, the large airways. It is often the most prominent symptom of airway obstruction in the pediatric patient. Proper management is possible only after a precise diagnosis has been established. Stridor is a symptom and not a diagnosis. It cannot be managed appropriately on the basis of a presumptive or inferential diagnosis.

Stridor is most often inspiratory. It typically originates from the larynx, upper trachea, or hypopharynx. The term stertor has been used to describe the low-pitched inspiratory snoring sound typically produced by nasal or nasopharyngeal obstruction.

Wheezing is the expiratory sound produced by the turbulent flow of air through constricted small airways (bronchioles). This sound is similar to, and frequently mistaken for, other intrathoracic conditions such as bronchomalacia, tracheomalacia, or foreign bodies in the trachea or bronchi.

FIGURE 1. The triangular aperture of the normal infant larynx
is approximately 7 mm x 4 mm, an area of 14 mm.²
When intubation or an upper respiratory tract infection
causes one millimeter of edema, the cross-sectional area
is reduced to 5 mm² , only 35% of normal.²

Obstructive lesions of the airways produce turbulent air flow. The pathophysiology of this phenomenon is explained by Bernoulli's principle. Figures 1 and 2 demonstrate the susceptibility of the laryngeal airway to 1 mm of edema.² The normal infant glottis is a triangular aperture approximately 7 mm in the anteroposterior dimension and 4 mm at the base in the posterior glottis. The cross-sectional area of 14 mm² is reduced to 5 mm² by 1 mm of edema, a reduction to 35% of the original area³ (Figure 1). In the low subglottic larynx, a similar reduction occurs. The normal newborn subglottic larynx has a diameter of 5–7 mm.

FIGURE 2. The normal newborn subglottic larynx has a diameter of 5–7 mm and a cross-sectional area of approximately 28.3 mm² . One millimeter of edema reduces the area to 12.6 mm² , 44% of normal. In a case of subglottic stenosis, where the diameter may be only 4 mm, the cross-sectional area of the lumen is 12.6 mm² . One millimeter of edema reduces this to 3.1 mm² , only 25% of the original.²

One mm of edema reduces a 6 mm diameter lumen to 44% of the original cross-sectional area (Figure 2). The change is even more dramatic in the presence of subglottic stenosis. For example, if the subglottic larynx has a diameter of only 4 mm, the cross-sectional area is 12.2 mm³ . One mm of edema reduces this to 3.1 mm² , only 25% of the original area! These data illustrate why infants with subglottic stenosis present with recurrent episodes of croup whenever they get a slight upper respiratory tract infection.

In a review of 219 patients whose primary presenting symptom was stridor,¹ all 150 boys and 69 girls were under 2 ½ years of age. More than half were 4 months or younger. The data accumulated in this study were most representative of chronic stridor—stridor that had been present for more than half of each patient's life. The large majority of cases (87%, Table 1) represented congenital anomalies. However, many of these babies do not have symptoms at birth. Sometimes stridor appears shortly thereafter or occurs later during infancy or childhood. It often appears slowly and is not severe except when the infant is stressed with feeding, crying, or certain positions. When the onset is slow or presents from birth, the etiology is usually congenital. The patients who present with symptoms of relatively short duration are more likely to have acquired lesions—infectious conditions, internal laryngeal trauma, bronchial foreign body, or tonsil and adenoid hypertrophy.

Congenital laryngeal anomalies accounted for the stridor in 60% of the patients studied.¹ Sixteen percent had congenital tracheal anomalies. Five percent had congenital bronchial anomalies. Baby boys had stridor more than twice as often as baby girls.¹ The most common causes are congenital anomalies, most occurring in the larynx and with decreasing frequency in the trachea and bronchi.

Cyanosis in the newborn

Obstruction of the respiratory system in the newborn may be an acute emergency requiring immediate accurate diagnosis and treatment. Cyanosis is evidence of extreme obstruction of the respiratory tract in the stridorous infant but must be differentiated from lesions of the cardiovascular, gastrointestinal, and central nervous systems.

Lesions of the cardiovascular and central nervous systems can be ruled out if the cyanotic infant is making a vigorous effort to breathe. Only with respiratory tract obstruction does a cyanotic infant make strenuous and active respiratory effort. Gastrointestinal system involvement may be due to tracheoesophageal fistula (TEF) or gastroesophageal reflux (GER). Both may produce symptoms of coughing, aspiration, choking, and pneumonia. GER may cause apnea, respiratory arrest, and even death in infants.

When it has been determined that a respiratory system abnormality is the cause of cyanosis, consideration is given to determine if the problem is related to the pleural cavities (as in spontaneous pneumothorax or diaphragmatic hernia), lung (as in hyaline membrane disease, congenital lobar emphysema, cystic adenomatoid malformation, or transient tachypnea), or if the symptoms are due to obstruction of the airway itself.

If the infant is completely or severely obstructed, he is immediately suctioned and the tongue pulled vigorously forward. The next step is to insert an oral airway and ventilate with mask and ambu bag. If the obstruction persists, a laryngoscope is used to lift the base of the tongue and epiglottis forward to visualize the larynx. If the larynx is patent, a small (2.0 or 2.5) endotracheal tube is placed carefully between the vocal folds and into the mid trachea. If the infant remains in severe distress after suctioning, it is concluded that the problem is related to the lower trachea, bronchi, lungs, or pleural cavities. A chest radiograph is obtained immediately.

Evaluation of the Noisy Baby

When anxious parents bring their stridorous infants for evaluation, the mnemonic "SPECS-R" is a helpful way to organize history-taking to determine the need for endoscopy in the operating room (Table 2).⁴ Accurate assessment of the severity of the obstruction is often difficult. Specific questions are asked to determine objectively whether the child truly is at risk. At one extreme, the family may have a cavalier attitude toward the infant's symptoms. On the other hand, the physician should not be coerced into referring an infant for bronchoscopy by over-anxious parents when endoscopy is not indicated. Specific information, such as a history of recurrent croup or the finding of a cutaneous hemangioma, may support the decision to refer.

The assessment of the infant with stridor may be focused by several generalizations that can be made regarding symptoms of airway obstruction (Table 3). In general, stridor produced by an obstructive lesion above the thoracic inlet (clavicles) is inspiratory. This is due to the dynamic nature of most of these lesions in which the structures collapse inward with the negative pressure created during inspiration. The exceptions are fixed lesions, such as subglottic stenosis, which do not change with respiration and therefore produce both inspiratory and expiratory stridor. Lesions of the nasopharynx (eg., adenoid hypertrophy), oropharynx (eg., micrognathia and macroglossia, tonsil hypertrophy), and hypopharynx (eg., base of tongue mass, retropharyngeal abscess) typically produce a low-pitched, wet sound similar to snoring. These infants would seem to require suctioning but the audible symptoms do not clear after suctioning. The inspiratory stridor of laryngomalacia is also low-pitched (and fluttering) but somewhat different in character. In contrast is the high-pitched inspiratory stridor associated with bilateral vocal cord paralysis.

Tracheomalacia and bronchomalacia, like asthma, typically produce stridor during expiration. If the extrathoracic trachea is significantly involved, the stridor may be biphasic. The pitch and phase of the stridor may therefore be helpful in localizing and diagnosing a lesion. While primary care physicians most frequently apply the label "tracheomalacia" to stridorous babies, laryngomalacia is five times more common, especially as a cause of inspiratory stridor.

These generalizations ("Laws") in Table 3 do have exceptions. For example, the first manifestation of airway obstruction in recurrent cases of respiratory papillomatosis of the larynx is most likely to be progressive obstruction during sleep—not awake with exertion as is the case for most laryngeal lesions. However, these "Laws" are helpful guidelines in localizing the problem during the initial assessment.

The physical examination begins with observation. The relative size of the mandible and tongue is evaluated. The infant is observed at rest and after stimulation. The level of alertness and muscular tone is assessed; hypotonic infants often have a weak cry and a diminished response to stimulation. Particular notice is taken of any nasal flaring, subcostal or suprasternal retraction, abdominal movement, and cyanosis. When dysphagia is a symptom, it may be helpful to give the infant a bottle to observe feeding. The character, quality, and severity of stridor are assessed and compared with the parents' description.

For auscultation, the bell of the stethoscope is held close to the infant's mouth and nose to determine whether the stridor is primarily inspiratory or expiratory and which phase of respiration is prolonged. The lungs are auscultated while the infant is still resting quietly before other diagnostic maneuvers cause the infant to cry, making worthwhile auscultation of the lungs and heart impossible. Examination of the nose, mouth, and palate is carried out last.

Monitoring

Objective data are helpful in determining the severity of respiratory compromise and the need for intervention in children who have loud stridor but do not appear to be in respiratory distress. Apnea and bradycardia monitors, continuous pulse oximeter, and transcutaneous CO₂ monitors provide objective information and can be used on an outpatient basis or during a brief hospitalization. Similarly, chronic hypoxia associated with cor pulmonale can be followed up with echocardiography. Polysomnography is useful in evaluating sleep disturbances resulting from airway obstruction. Although these studies may not provide diagnostic information about the specific site of the obstructing lesions, they can be used to assess the severity of the airway obstruction and can help the clinician decide if further investigtion or intervention is needed.

Consultation

In addition to the consultation with a pediatric otolaryngologist, infants and children (particularly those with multiple congenital anomalies) frequently benefit from consultation with a specialist in pulmonary medicine, cardiology, neurology, genetics, endocrinology, anesthesia, allergy and asthma. Any child who is wheezing and on medication for reactive airways disease, or who has not been evaluated by the asthma service, is referred for consultation prior to bronchoscopy. Reactive airways disease that is atypical or unresponsive to medical management is a common indication for bronchoscopy.

Radiologic Evaluation

The preoperative radiographic assessment of the infant with moderate or severe upper obstruction includes soft tissue posteroanterior and lateral radiographs of the neck (airway films, Figure 3) and chest. When there is a history of dysphagia or aspiration, barium esophagram and/or rehabilitative swallow study may be obtained. If tracheal compression is observed at the time of endoscopy, postoperative computed tomography of the chest is performed with contrast medium.

FIGURE 3A [left]. Normal airway. Lateral view. The epiglottis (arrow), adenoids (A), and tonsils (T), are indicated. Air is seen in the laryngeal ventricle (V). FIGURE 3B [right]. Normal airway. AP view. The right laryngeal ventricle (V) is below the right false cord and above the right vocal cord. The inferior apex of the pyriform sinuses (P) indicates the level of the vocal cord.

Flexible Laryngoscopy in the Office

The complete assessment of the noisy baby with mild symptoms of upper airway obstruction may be concluded with one office visit to the otolaryngologist. If the family answers negatively to all the SPECS questions (Table 2), and if the radiographic evaluation is negative, then awake flexible laryngoscopy is carried out in the office. Most often, a diagnosis of laryngomalacia is confirmed, and the family is given instructions to follow up with the primary care physician, but to call if symptoms progress.

Flexible laryngoscopy may be considered an extension of the physical examination. In otherwise healthy infants, it is quite safe when carried out by trained personnel with appropriate precautions. Suction and oxygen are available, and the endoscopist is assisted by trained nursing personnel.

The child is restrained gently. The small flexible laryngoscope is lubricated and passed through the nose to visualize the nasal passages, nasopharynx, and larynx (Figure 4). Topical anesthesia and sedation are not necessary. Vocal cord mobility is assessed and the dynamics of the supraglottic larynx are studied carefully. While the vocal cords can usually be assessed for mobility, a detailed examination of the larynx is not possible. Supraglottic structures and the position of the larynx sometimes obstruct adequate visualization of the vocal cords. No conclusions can be made regarding the subglottic larynx or trachea; in the absence of topical anesthesia, sedation, and complete monitoring, no attempt is made to pass the scope beyond the vocal cords.

FIGURE 4. Office flexible laryngoscopy for diagnostic purposes in the infant with noisy breathing. Video documentation can be made with a hard copy for the permanent medical record.

Which infants need diagnostic laryngoscopy and bronchoscopy?

Under certain conditions, infants need to be taken to the operating room for a complete endoscopic evaluation. These conditions include any positive indicators from the SPECS-R mnemonic, any significant findings at the time of flexible laryngoscopy, and any significant congenital or medical problems, such as congenital heart or pulmonary disease, that may increase the risk of office laryngoscopy.

Because infants are preferential nasal breathers for periods varying from days to weeks, nasal obstruction and nasopharyngeal obstruction can lead to asphyxiation. Therefore, any lesion from the nose^6–8 to the bronchi can produce life-threatening obstruction, most often manifested by stridor.

A few final observations will be of interest. Approximately 45% of infants and children with stridor were noted to have at least two anomalies.³ Well over half of these are anomalies of the respiratory system and may have contributed to the patient's stridor.

One-fourth of the children referred for evaluation of stridor had been treated for an erroneous presumptive diagnosis.¹ The most common misdiagnoses were asthma, croup, bronchiolitis, laryngomalacia, and bronchitis. The delay from time of onset of symptoms to establishing a precise diagnosis at endoscopy ranged from one day to sixteen months; the mean time was four months.

REFERENCES

1. Holinger LD: Etiology of stridor, Ann Otol Rhinol Laryngol 1980; 89:397–400.

2. Holinger LD: Evaluation of stridor and wheezing. In Pediatric Laryngology & Bronchoesophagology, Holinger LD, Lusk RP, and Green CG (eds.), Philadelphia: Lippincott-Raven Press, 1997, 41–48.

3. Holinger PH, Johnston KC: Factors responsible for laryngeal obstruction in infants. JAMA 1950;143:1228–32.

4. Holinger LD: Diagnostic endoscopy of the pediatric airway. Laryngoscope 1989;99:346–348.

5. Poznanski AK: Radiology. In Pediatric laryngology & bronchoesophagology, Holinger LD, Lusk RP, and Green CG (eds.), Philadelphia: Lippincott-Raven Press, 1997, 49–64.

6. Arlis H, Ward RF: Congenital nasal pyriform aperture stenosis. Arch Otolaryngol Head and Neck Surg 1992;118:989–991.

7. Benjamin B: Evaluation of choanal atresia. Ann Otol Rhinol Laryngol 1985;94:429–432.

8. Lusk RP, Muntz HM: Nasal obstruction in the neonate secondary to nasal lacrimal duct cysts. Int J Ped ORL 1987;13:315–322.

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