Neonatal laryngotracheal stridor

　　Firstly, etiology

　　Stridor is mostly caused by diseases of the larynx or nearby tissues. Common causes include the following.

　　1. Congenital

　　Congenital simple laryngotracheal stridor (laryngotracheal cartilage软化症), congenital laryngotracheal developmental anomaly (laryngeal web, epiglottic bifidity, macroepiglottis, subglottic stenosis, tracheal stenosis, etc.), congenital abnormality of great vessels (double aortic arch), congenital laryngeal cyst or tumor (laryngeal cyst, laryngeal vascular tumor, laryngeal papilloma, laryngeal thyroid, etc.).

　　2. Acquired

　　Traumatic laryngotracheal stridor (birth injury, laryngeal edema, acquired subglottic stenosis), neurogenic laryngotracheal stridor (vocal cord paralysis, laryngeal neuromuscular dyscoordination).

　　Secondly, pathogenesis

　　Stridor is caused by turbulent airflow through the narrow segment of the airway during inspiration or expiration.

　　1. Anatomical and physiological characteristics

　　Newborns are prone to narrowing due to the smaller diameter of the airway, and the underdeveloped cartilage supporting the airway makes it prone to twisting and collapse, therefore the airway of newborns is more prone to physiological narrowing than other age groups.

　　2. Inspiratory stridor

　　The supraglottic segment is the weakest part in neonates, and obstructive diseases at this site often cause inspiratory stridor, such as micrognathia or macroglossia, which can all cause airway obstruction due to the tongue tilting backward.

　　3. Biphasic stridor

　　The larynx is the narrowest part of the neonatal airway anatomy, and diseases such as congenital laryngomalacia, vocal cord paralysis, subglottic stenosis, laryngeal web, subglottic vascular tumor, and laryngeal cyst can all cause laryngeal obstruction. The airflow is affected equally during inspiration and expiration, therefore presenting as typical biphasic stridor.

　　4. Inspiratory stridor

　　Congenital anomalies of the trachea and bronchi are relatively rare within the thorax, such as tracheal softening, tracheal stenosis, congenital abnormality of great vessels compressing the airway, or airway inflammation caused by recurrent gastroesophageal reflux, which can all lead to airway obstruction in this section, manifesting as inspiratory stridor.

　　It can be complicated by hypoxemia; when secondary respiratory tract infection occurs, the symptoms of respiratory distress become more severe, and the secretion of respiratory tract secretions is not smooth, and sputum sounds appear. Long-term stridor can lead to pigeon chest. Congenital simple laryngomalacia is the most common cause of laryngomalacia in the neonatal period, accounting for about 60% to 70% of neonatal laryngomalacia. The stridor is usually a high-pitched crowing sound, but can also be a low-pitched vibratory sound, generally occurring only during inhalation, and in severe cases, during exhalation as well. The symptoms are usually intermittent, disappearing during sleep or quiet times, and becoming obvious during crying and restlessness. The stridor is alleviated or disappears when lying on the stomach, and is more pronounced when lying on the back. During stridor, there may be depression of the suprasternal notch, intercostal spaces, and upper abdomen, but the growth and development are good, and the crying is normal. The symptoms of stridor often gradually disappear on their own between 18 and 24 months without special treatment. In some severe cases, respiratory difficulties and cyanosis may occur.

　　1. Congenital Simple Laryngomalacia

　　Congenital simple laryngomalacia refers to the excessive softness of laryngeal tissue, which collapses inward during inhalation, blocking the upper orifice of the larynx and causing stridor. The softness of the laryngeal tissue may be due to malnutrition during pregnancy, calcium or other electrolyte deficiencies or imbalances in the fetus, hence it is also called laryngomalacia. It is the most common cause of laryngomalacia in the neonatal period, accounting for about 60% to 70% of neonatal laryngomalacia. The stridor is usually a high-pitched crowing sound, but can also be a low-pitched vibratory sound, generally occurring only during inhalation, and in severe cases, during exhalation as well. The symptoms are usually intermittent, disappearing during sleep or quiet times, and becoming obvious during crying and restlessness. The stridor is alleviated or disappears when lying on the stomach, and is more pronounced when lying on the back. During stridor, there may be depression of the suprasternal notch, intercostal spaces, and upper abdomen, but the growth and development are good, and the crying is normal. The symptoms of stridor often gradually disappear on their own between 18 and 24 months without special treatment. In some severe cases, respiratory difficulties and cyanosis may occur.

　　2. Laryngeal Palsy

　　Laryngeal palsy is a common cause of laryngomalacia in newborns, ranking second only to laryngomalacia, with unilateral laryngeal palsy being more common, often occurring on the left side. This is due to the longer and more tortuous left recurrent laryngeal nerve, which is more susceptible to traction and injury at birth. It can be accompanied by injuries to other peripheral nerves on the same side, such as facial nerve palsy, brachial plexus palsy, and phrenic nerve palsy. If there is no significant history of birth trauma or peripheral nerve injury, unilateral laryngeal palsy should be ruled out for cardiovascular, pulmonary, or esophageal lesions, as the left recurrent laryngeal nerve encircles the distal opening of the aortic arch ductus arteriosus, making it susceptible to stretching by dilated blood vessels. The right recurrent laryngeal nerve is protected by being located below the left subclavian artery, so unilateral right laryngeal palsy is extremely rare. The hoarseness in unilateral laryngeal palsy is biphasic, often accompanied by hoarseness or aphonia, without cyanosis or feeding difficulties, and is usually self-resolving without the need for treatment. Bilateral laryngeal palsy is often central, caused by hypoxia injury to the brainstem during prenatal or perinatal periods. It can be accompanied by swallowing difficulties and other cranial nerve injuries, with weak crying, high-pitched biphasic laryngomalacia, and respiratory distress. Sometimes, tracheal intubation or tracheotomy may be necessary, and some children can recover slowly on their own. Therefore, further surgical intervention should be delayed until after the age of 4.

　　3. Congenital larynx

　　Abnormal tracheal development This group of diseases includes various anatomical abnormalities that cause laryngeal and tracheal stenosis. Congenital laryngeal web is present at birth with laryngophonia, hoarseness, or weakness in voice, and larger webs can cause dyspnea. Early diagnosis and treatment are necessary. Congenital subglottic elastic cone tissue hypertrophy or cricoid cartilage deformity can cause subglottic stenosis and obstruction. Severe cases may have laryngophonia at birth, but normal voice and crying. Congenital tracheal stenosis can be caused by intrinsic tracheal lesions (such as absent tracheal cartilage rings, softened tracheal rings, tracheal web, tracheal cysts, etc.) or extrinsic lesions (such as neck tumors, mediastinal tumors, or vascular abnormalities, etc.) that compress the trachea. Children often have persistent laryngophonia at birth or soon after, being more pronounced during expiration. Normal crying and voice, but severe cases may have dyspnea.

　　4. Congenital major blood vessel abnormalities

　　Abnormalities of major blood vessels are caused by maldevelopment of the aortic arch or malposition of one or more major blood vessels originating from the aorta. When these abnormal vessels form a tight vascular ring, they can compress the trachea or esophagus. The vascular ring formed by double aortic arches is the most tight, and persistent laryngophonia often appears at birth or soon after, being more pronounced during expiration. Severe cases may have dyspnea and cyanosis, while difficulty in swallowing is not common, but eating can worsen laryngophonia. Since the vascular ring formed by the double aortic arches cannot increase in size with the growth of the child, the compressive symptoms become more severe as the child grows, and early surgical correction is needed. Other vascular rings formed by major blood vessels (such as right aortic arch, aberrant subclavian artery,无名 artery, pulmonary artery, etc.) and arterial bands or ducts are mostly open and can increase in size with the growth of the child, so they rarely cause symptoms in the neonatal period.

　　5. Congenital laryngeal cyst or tumor

　　Congenital laryngeal cysts, laryngeal thyroid, or laryngeal tumors (hemangiomas, papillomas) can cause laryngophonia in newborns, manifested as biphasic stridor with hoarseness or aphonia, the degree of dyspnea being determined by the size of the tumor.

　　Tumors of nearby tissues such as cervical cystic hygroma, thyroid cystic duct cyst, congenital巨舌 or vagus thyroid at the base of the tongue, and congenital thyroid goiter can cause respiratory distress, but rarely cause stridor.

　　6. Other

　　The excitability and incoordination of the laryngeal nerves and muscles may also be a factor in the development of laryngophonia. Due to the higher excitability of the vagus nerve in newborns, even slight stimulation of the respiratory and gastrointestinal tracts can become pathological impulses. These impulses are transmitted through the vagus nerve to the laryngeal center at the base of the fourth ventricle, causing laryngophonia. Cholinergic blocking drugs (scopolamine, atropine) are effective medications for blocking neural laryngophonia. In addition, children who have had long-term tracheal intubation and mechanical ventilation may experience laryngophonia after extubation due to local edema or subglottic stenosis caused by injury to the vocal cords or cricoid cartilage. Laryngophonia can occur in about 10% of intubated children. Using soft tracheal tubes, skilled intubation techniques, good fixation, and the use of dexamethasone before extubation can reduce the incidence of this complication.

　　It is generally believed that due to malnutrition during pregnancy, fetal calcium deficiency, it is often possible to soften the laryngeal cartilage, so attention should be paid to doing a good job of prenatal health care, strengthening prenatal nutrition, and preventing and treating various infectious diseases. Pay attention to preventing colds and being startled to avoid respiratory tract infections and laryngospasm, which can exacerbate laryngeal obstruction. If the attack is severe with difficulty in breathing, adjust the baby's position to the lateral side to alleviate symptoms. In rare cases of severe laryngeal obstruction, tracheotomy may be required.

　　1. Direct laryngoscopy

　　It is the most important diagnostic method. Direct laryngoscopy of congenital simple laryngomalacia shows soft and relaxed laryngeal tissue, the upper laryngeal tissue curls inward during inspiration, and is blown out during expiration. If the epiglottis is lifted or extended to the laryngeal vestibule with a direct laryngoscope, the hoarseness sound disappears, and the diagnosis can be confirmed. Laryngeal cysts, tumors, bifid epiglottis, and laryngeal paralysis can only be diagnosed by laryngoscopy.

　　2. Bronchoscopy

　　Subglottic and tracheal lesions must be diagnosed by bronchoscopy, and bronchoscopy may be necessary.

　　3. X-ray examination

　　Anteroposterior and lateral X-ray films of the neck and chest, as well as esophageal barium swallow examination, are helpful for diagnosing the cause of neonatal laryngomalacia.

　　4. Ultrasound examination

　　If necessary, a cardiac ultrasound examination can help in the diagnosis of the cause of neonatal laryngomalacia.

　　Parents of congenital laryngomalacia do not need to be anxious. If the symptoms are not too severe, most children can recover spontaneously around the age of 2. You can give the child some calcium supplements, get plenty of sunlight, and prevent colds, and avoid upper respiratory tract infections and laryngeal inflammation. For children with particularly severe symptoms accompanied by difficulty in breathing, hospital treatment is required. Eat more vitamin D-rich foods, such as:

　　1. Cod liver oil;

　　2. Animal liver, such as chicken liver, duck liver, pork liver, beef liver, sheep liver, etc.;

　　3. Various fatty fish, such as herring, salmon, tuna, sardine, mackerel, eel, catfish, etc.;

　　4. Various whole milk, cheese, and butter (note, the content in skimmed milk is very low, while the content in fortified AD milk is the highest).

　　1. Treatment

　　Treatment mainly focuses on the treatment of the primary disease and symptomatic treatment.

　　1. General treatment

　　Strengthen nursing care to prevent triggers such as colds, diarrhea, and to prevent complications. Congenital simple laryngomalacia generally does not require special treatment; it only requires strengthening nursing care and attention to prevent respiratory tract infections. As the laryngeal cavity enlarges and the laryngeal tissue gradually becomes normal between 18 to 24 months, the hoarseness will gradually disappear. Instruct the parents to pay attention to preventing colds and being startled to avoid respiratory tract infections and laryngospasm, which can exacerbate laryngeal obstruction. Pay attention to maintaining water, electrolyte, and acid-base balance. At the same time, provide adequate calcium supplements, add complementary foods in a timely manner, and other auxiliary treatments. If the attack is severe with difficulty in breathing, adjust the baby's position to the lateral side to alleviate symptoms, and treat the symptoms accordingly.

　　2. Respiratory Tract Infection

　　For children with pneumonia, antibiotic treatment is given, and mechanical ventilation can be used for children with concurrent respiratory failure; if there is sputum rales on lung auscultation, ultrasonic nebulization and suction, frequent back patting, and good respiratory care should be performed.

　　3. Severe Laryngeal Edema

　　Dexamethasone and 10% calcium gluconate can be used to reduce edema; some children may use antispasmodic and bronchodilator drugs. In severe cases of laryngeal obstruction, tracheotomy may be performed.

　　4. Neurogenic Laryngospasm

　　Scopolamine can be tried for neurogenic laryngospasm, starting with low doses, 0.02mg/kg intravenous infusion, once a day. If ineffective, the dose can be gradually increased to 0.04-0.06-0.08mg/(kg·d) until the symptoms of laryngospasm disappear.

　　5. Hypocalcemic Laryngospasm

　　Laryngospasm to wheezing seen in infantile tetany of the hands and feet is treated with calcium and vitamin D.

　　6. Surgical Treatment

　　Patients with respiratory distress caused by congenital abnormalities of the larynx and trachea, vascular anomalies, and congenital laryngeal cysts and tumors must undergo early surgical treatment. The treatment of subglottic stenosis depends on the degree of obstruction; mild cases do not require special treatment and the symptoms will naturally disappear as the laryngeal cavity enlarges, while severe cases may require tracheotomy.

　　II. Prognosis

　　The prognosis varies depending on the original cause and severity, from congenital simple laryngomalacia, which can usually disappear with growth and development, to some children who still have wheezing after respiratory tract infections, straining, and crying throughout their childhood. Wheezing secondary to various injuries can also improve with the resolution of the primary disease and injury. Wheezing caused by tetany of the infant's hands and feet, cysts, laryngeal edema, etc., can be cured as the cause is eliminated.