TITLE: STRIDOR IN NEONATES, INFANTS, AND CHILDREN
SOURCE: Dept. of Otolaryngology, UTMB, Grand Rounds
Date: April 15, 1998
Resident Physician: Ravi Pachigolla, MD
Faculty: Ronald Deskin, MD
Series Editor: Francis B. Quinn, Jr., MD

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 "This material was prepared by resident physicians in partial fulfillment of educational requirements established for the postgraduate training program of the UTMB Department of Otolaryngology/Head & Neck Surgery and was not intended for clinical use in its present form. It was prepared for the purpose of stimulating group discussion in a conference setting. No warranties, either express or implied, are made with respect to accuracy, completeness, or timeliness. The material does not necessarily reflect the current or past opinions of members of the UTMB faculty and should not be used for purposes of diagnosis or treatment without consulting appropriate literature sources and informed professional opinion."


DEFINITION OF STRIDOR

Stridor is the noise that is mechanically produced through a partially obstructed airway. Stridor in and of itself is not a diagnosis but merely a symptom of underlying pathology. The stridor can be defined as a variably pitched respiratory sound caused by tissue vibration through an area of decreased caliber. Airway obstruction at the level of the nasal cavities produces inspiratory low-pitched sound called stertor or snoring while supraglottic lesions tend to produce high pitched sounds. Subglottic lesions tend to produce biphasic high pitched stridorous sounds. Lower respiratory tract lesions produce characteristic expiratory wheezing.

A basic knowledge of the Venturi principle is essential in understanding these abnormal airway noises. The movement of a gas through a partially closed flexible tube obeys the laws of physics. With linear movement of the gas, lateral pressure decreases causing a narrowing of the tube. This phenomenon is the Venturi principle. The flexible airway of the child is subjected to these forces and this pattern of intermittent flow creates a pattern of vibrations of the lumen wall that results in audible sound, such as stridor. Most stridulous sounds are musical, last greater than 200 msec, and are usually inspiratory and harmonious. The supraglottis, tongue and pharynx is a prime example of the Venturi principle. These tissues are loosely supported and often falls into the airway during inspiration. Vigorous inspiratory efforts, particularly when associated with air hunger, create a relative increase in pharyngeal pressure. Thus the stridor produced is inspiratory and high-pitched.

Patients with glottic and subglottic obstruction usually have inspiratory stridor initially which becomes expiratory as obstruction increases. The glottis and subglottis are fixed in size and because of the tight supporting vocal ligaments, are less affected by the Venturi principle. Airflow is limited to absolute lumen size because the airway is fixed. When stridor does develop here, it usually signifies significant respiratory compromise as the airway has been considerably narrowed.

The time available to make a diagnosis may be only a matter of minutes if the stridor is sudden and severe with diminished ventilatory exchange. In the absence of respiratory distress, a prompt but more thorough investigation can be made before initiating medical or surgical therapy.

HISTORY AND PHYSICAL

The physician should first establish the duration of the stridor, presence of respiratory distress, and relationship to feedings and to positionings. Other non-stridorous causes of airway obstruction must be ruled out including intracranial hemorrhage, large abdominal mass, neuromuscular diseases and other intrathoracic causes. A careful history should include time of onset, initiating trauma if any, characteristics of the cry, and congenital anomalies. Variability of symptoms should be ascertained. Other related symptoms, including hoarseness, feeding difficulties, and sleep disturbances such as stertor should also be entertained. The respiratory phase of the stridor should be noted. A history of prematurity and/or endotracheal intubation is also important.

The initial physical exam assesses the severity of the respiratory distress and need for emergency airway management. Careful noninvasive inspection is important to avoid exacerbating airway compromise. It is important to note respiratory rate and level of consciousness as these two indicators signify the severity of the situation. Tachypnea usually manifests first and with later progressive obstruction, shallow breathing with mental status changes ensues. Retractions, either sternal or supraclavicular does not necessarily preclude a thorough investigation. The child should be asked to speak if it is able to do so. It is important to record intensity, pitch, respiratory phase and to outline a differential diagnosis. The stethoscope can be held a few centimeters from the nose and mouth and larynx and trachea to establish the pattern of stridor without actually touching the patient. If the patient is not in imminent respiratory distress, awake flexible nasopharyngoscopy can be performed and this is sufficient for the diagnosis of supraglottic and nasopharyngeal lesions. Some general assumptions can be made on the basis of the physical exam. With supraglottic laryngeal obstruction, stridor is generally inspiratory and retractions are not present unless the obstruction is quite severe. Patients may have problems feeding. Glottic obstruction may produce a hoarse voice or aphonia while feeding and cough may be normal. Subglottic obstruction may have a barking cough as a symptom and can mimic glottic obstruction.

Radiography assists in the evaluation of stridor. Plain films should first be performed including AP and lateral views of the neck to provide evidence of collapse and obstruction. A normal stairstep pattern should be seen on lateral neck views. High KV techniques are also useful for an AP view of the larynx taken during inspiration. This provides superior anatomical detail revealing subglottic stenosis, cysts, or hemangiomas. A normal right lateral deviation just below the thoracic inlet caused by the presence of the aortic arch should be noted. Chest x-rays are useful in delineating air trapping, atelectasis, and radio-opaque foreign bodies. Airway fluoroscopy provides additional information regarding the airway dynamics. CT and MRI may be useful in diagnosing retropharyngeal abscesses and vascular anomalies causing airway compression.

Only endoscopy can establish a true diagnosis for stridor. After flexible nasopharyngoscopy (best evaluation of vocal cord motion) has been performed, attention then turns to rigid endoscopy. Slow masked inhalation is useful to preoxygenate the infant and then endoscopy is begun with a diagnostic laryngoscope placed into the vallecula with an open lumen bronchoscope for ventilation and diagnosis. Xylocaine spray may applied topically at the beginning of endoscopy. Endoscopy begins with complete visualization of the supraglottis, glottis, subglottis, measurement of the air passage, and examination of mucosal contour. At the end of the procedure, when the anesthesia level lightens, vocal cord mobility may be assessed, however, with the attendant risk of laryngospasm. As stated earlier, the best assessment of vocal cord motion is with flexible nasopharyngoscopy.

LARYNGOTRACHEOBRONCHITIS

Acute croup is the most common cause of acute stridor in children caused by the parainfluenza virus typically occurs in fall and spring. It is a generally benign condition that is manifested in a young infant usually with a low grade fever, barking cough, and occasionally biphasic stridor occurring over a period of days. A "steeple" sign may be visible on AP views of the subglottic airway. Stridor usually resolves over several days and few patients require hospitalization. Tachypnea, retractions, and cyanosis indicate prompt hosptalization. Hospitalization usually involves treatment with cold humidification, oxygen, racemic epinephrine, and occasionally steroids. One dose of steroids seems to be effective in a dose of 1 mg per kg. Intubation is necessary only for severe respiratory distress and may be required for 4 to 5 days.

EPIGLOTTITIS

Epiglottitis is bacterial in origin with H.Flu B being the predominant organism. Children are usually affected between the ages of 2 to 6. It usually develops suddenly with high fever, drooling, sitting forward, and odynophagia. The infant is rushed to the operating room where intubation is performed in a controlled setting followed by examination of the hypopharynx, revealing a cherry red, swollen epiglottis. Cultures are obtained from the epiglottis and the patient is left nasally intubated for 2 to 3 days until the swelling subsides and the patient is breathing around the tube. Antibiotics should be given to cover for B-lactamase producing Haemophilus Influenza. Since the introduction HIB vaccination, incidence of epiglottitis has decreased significantly. This diagnosis should be entertained when the child has a history of URI that has prevented it from receiving the usual vaccinations.

LARYNGOMALACIA

This is the most common cause of chronic pediatric stridor causing approximately 60% of stridor seen in newborns. The condition usually becomes apparent shortly after birth and worsens over the next few months and usually resolves by 18 months. Local neurologic factors have been implicated in the flaccidity of the supraglottis in these infants. Flexible nasopharyngoscopy reveals inward collapse of the aryepiglottic folds and cartilages. The stridor is worsened while crying or in an excited state, often in the supine position where the supraglottic structures may collapse inward. Pectus excavatum is occasionally seen but the relationship to laryngomalacia remains unclear. Debate continues about the exact cause of laryngomalacia but the predominant theories suggest that immature neuromuscular control of the cartilages contributes to the inward collapse. The neuromuscular theory is enhanced by the fact that GERD sometimes coexists. If feeding difficulties, apnea, cyanosis or failure to thrive develop, surgical measures may be necessary. Aryepiglottiplasty may be performed using the laser to excise redundant mucosa over the arytenoid and cuneiform cartilages. The mucosa between the arytenoids should be preserved to prevent interarytenoid scarring. If this does not work, tracheostomy may be necessary.

SUBGLOTTIC STENOSIS

This occurs when the airway lumen at the level of the cricoid measures less than 3.5 mm. Most commonly, this condition results from intubation ation of premature infants. Congenital subglottic stenosis, however, can also exist. Symptoms may include recurrent "croup", biphasic stridor, retractions, with a normal cry but air hunger may lead to feeding difficulties. Endoscopy is required to make the diagnosis. It is important to distinguish congenital subglottic stenosis from acquired subglottic stenosis. Congenital stenosis results from incomplete canalization of the subglottis and usually has a milder presentation. Incidentally, trisomy 21 is associated with a higher incidence of congenital subglottic stenosis. Most congenital stenoses improve as the child’s larynx grows and patients generally only become symptomatic with upper respiratory infections.

Subglottic stenosis can be defined as a diameter of less than 4 mm in full term infant and less than 3 mm in a premature infant and the stenosis is usually most significant 2 to 3 cm below the vocal cords. The stenosis may be membranous or cartilaginous. The anterior cricoid split operation may be appropriate for congenital cartilaginous stenosis where a shelflike plate exists anteriorly and a posterior opening is apparent. As stated earlier, acquired subglottic stenosis is generally more severe than congenital subglottic stenosis. A question exists regarding development of subglottic stenosis related to length of intubation. Generally speaking, risk for subglottic stenosis increases proportionately through the first week of intubation. After the first week, however, the risk for subglottic stenosis tends to level off.

Criteria for performing an anterior cricoid split include two failed extubations, weight greater than 1500 gms, no assisted ventilation for 10 days prior to evaluation, normal true vocal cord mobility, oxygen requirements less than 35%, no CHF, no respiratory infection and no antihypertensive medication for 10 days prior to evaluation. The procedure involves rigid endoscopy first to rule out subglottic hemangioma, cysts or other laryngeal pathology. After a horizontal skin incision over the cricoid, skin flaps are elevated and a single vertical incision is made through the cricoid and upper two tracheal rings and the incision is extended superiorly to include the lower two thirds of the thyroid cartilage avoiding the anterior commissure. 4-0 prolene stay sutures are placed and the ETT left in place. The skin is loosely approximated leaving a penrose drain. The ETT is left in place 7 to 10 days until the swelling subsides and then the patient may be extubated. Steroids may be given 48 hours pre extubation. Laryngotracheoplasty may also be considered as an alternative to tracheostomy in these patients. Similar to ACS, this involves placing either auricular or costal cartilage in the anterior cricoid and trachea. Smaller stenoses may only require auricular cartilage but stenoses greater than 90% or a a stenosis of length greater than 1.5 cm may require a costal cartilage graft. The key is to close mucoperichondrium to mucoperichondrium since this allows graft stabilization. Staged reconstruction may be necessary with both anterior and posterior grafts. Stents are sometimes required in this situation although commissure blunting and scarring become an issue. The costal cartilage is fashioned to fit the defect again insuring that the mucoperichondrium is sutured to mucoperichondrium.

SUBGLOTTIC HEMANGIOMA

Subglottic hemangioma is a rare cause of stridor in infants. 50% of children with these hemangiomas have associated cutaneous lesions. The hemangioma does not usually present until the patient reaches 3 to 6 months of age and is sometimes worsened by agitation secondary to venous engorgement. Stridor may be biphasic but cry and hoarseness are unaffected. Lateral radiographs routinely show posterior subglottic masses and thus the diagnosis can be entertained. However endoscopy is required to make a definitive diagnosis. Because these lesions usually spontaneously involute, treatment should be reserved for those cases where frequent respiratory distress occurs. Gentle palpation confirms the lesion's softness. More females are affected than males. A left posterior predominance to the lesion may exist. Multiple treatment modalities exist to treat subglottic hemangioma including steroids, laser ablation, and even interferon in resistant cases. Steroids seem to work by inhibiting angiogenesis. Lasers should be used conservatively and staged procedures may be necessary. Lasers are best for isolated lesions and not for circumferential lesions with the main complication being subglottic stenosis. Interferon alpha should be used sparingly in those resistant cases that often require trachs. Interferon is thought to interfere with endothelial locomotion. All these various therapies are effective in about 60%-80% of cases.

VOCAL CORD PARALYSIS

Weakness and paralysis of the vocal cords is the second most common cause of neonatal stridor. Congenital malformations that impinge on the brainstem may cause bilateral vocal cord paralysis necessitating an airway emergency. Bilateral paralysis may cause a normal cry with severe respiratory stridor and distress This is due to the traction on the vagus nerves (eg. from an intracranial bleed). the usual presentation of unilateral vocal cord paralysis is hoarseness that sometimes improves when the patient lies down on the side with the paralyzed vocal cord since gravity allows the vocal cord to settle. Unilateral paralysis usually has a weak cry but airway intervention is only occasionally necessary. The other cord tends to compensate with time. Most cases are idiopathic and flexible nasopharyngoscopy routinely makes the diagnosis. This is the second most common cause of infantile stridor especially following a difficult delivery or cardiac or great vessel surgery.

VASCULAR ANOMALIES

Congenital anomalies of the great vessels account for about 5% of cases of stridor in children. Airway symptoms arise from compression. Anomalies include anomalous innominate artery, double aortic arch, retroesophageal right subclavian artery. Clinical manifestations vary and can include biphasic sounds with grunting with worsening with agitation. Apnea is a common manifestation of innominate artery compression and may be life threatening. A CT scan is diagnostic but endoscopy may also be required to document luminal narrowing. MRI may be superior to CT to completely assess vascular anomalies.

LARYNGEAL WEBS

These are uncommon anomalies usually resulting from incomplete canalization of the larynx. Symptoms are readily apparent at birth with weak cry, aphonia and sometimes respiratory distress. Emergency trach or intubation is occasionally required. Thinner webs may be treated endoscopically with scissors or laser while thicker webs sometimes require open laryngofissure and repair with keel placement.

LARYNGOTRACHEAL CLEFTS

This is a rare congenital anomaly that has a high mortality because of delay in diagnosis. Patients often present with feeding problems including coughing, choking, and aspiration. This condition results from failure of fusion of the posterior cricoid lamina during gestation and may extend inferiorly a considerable distance. Endoscopy is required to make the diagnosis and it should always be suspected by stenting the posterior larynx with the ETT. Treatment includes lateral pharyngotomy, anterior laryngofissure and other approaches to allow laterally based mucosal flaps to fill in the cleft. Repair is done in layers. Complications include posterior glottic stenosis and separation of the repair.

FOREIGN BODIES

Foreign bodies may cause of stridor in newborns and infants and a high degree of suspicion is always warranted. Immediate stridor accompanied by choking is strongly suggestive of a foreign body. Prompt management is necessary in these cases and even esophageal foreign bodies may impinge on the trachea causing stridor or other adventitious sounds. Lower airway foreign bodies may induce air trapping with atelectasis of the normal side and hyperinflation of the affected side. A coordinated team effort between anesthetist and otolaryngologist is essential in providing appropriate care. Bronchoscopes, suction tips, and forceps should be readily available. Usually, slow mask inhalation induction is performed followed by passage of a laryngoscope and then a ventilating bronchoscope through which various forceps may be passed to allow removal of the foreign object. The object may be drawn into the endoscope for removal or may have to be turned sagitally for removal through the vocal cords. Practice on a similar object on the side table with the appropriate instrument assists in removal. Atropine may be given to reduce bradycardia and secretions. Granulation tissue may have to be removed in order to gain access to the foreign body. Complications include laryngeal edema and traumatic laryngitis.

GENERAL INFORMATION ON TIME COURSE OF STRIDOR

Early onset stridor is usually vocal cord paralysis, laryngeal web or laryngeal cleft whereas delayed onset stridor is usually laryngomalacia, subglottic stenosis, vascular anomalies or subglottic hemangioma..



Discussion by Ronald W. Deskin, M.D.

Grand Round Comments

Subglottic Stenosis

It should be noted that subglottic stenosis produced by prolonged intubation in the premature child for pulmonary problems has decreased considerably since the wide spread use of Surfactant. It is also still generally felt that the incidence of subglottic stenosis relates to duration of intubation, choice of tube size, and whether or not infant has had premature accidental repeated extubations and re-intubations.

The use of the laser to treat subglottic hemangiomas is generally limited to lesions that are causing progressive obstruction and are able to be removed by partial resection with a laser. Wide spread use of the laser for circumferential hemangiomas is not recommended due to potential scarring.

 


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