xRead - February 2023

Zalzal & Zalzal

302

Stridor is not a diagnosis, but a sign of a condition that can range from benign, self limited disorders to rapidly progressing airway obstruction. Any child presenting with stridor as an acute, chronic, or recurring problem should be evaluated in a systematic and orderly manner with appropriate studies, in either an inpatient or an outpatient setting. This article delves into the diagnosis and management of stridor in infants, with a focus on conditions resulting in inspiratory stridor secondary to laryngeal pathologic condition with an emphasis on laryngomalacia. Before discussing the cause of stridor, discussion of respiratory noises of infancy must first be described, as follows: Inspiratory stridor : High-pitched respiratory noise caused by turbulent airflow during inspiration, usually secondary to a restricted larynx or upper trachea. Expiratory stridor : A harsh respiratory noise caused by turbulent airflow during expi ration, with obstruction being within the lower airway, such as the lower trachea or bronchi. Biphasic stridor : A harsh respiratory noise throughout the entire respiratory cycle, signaling a lesion of the midtrachea, glottis, and subglottis. Stertor: A low-pitched, “snoring-like” respiratory noise during inspiration, typically originating from the nasopharynx. Wheezing : A whistling respiratory noise with expiration, best heard within the lungs secondary to restricted airflow through the bronchioles. The upper airway in children is funnel shaped, with the cricoid being the narrowest portion of the infant airway. At birth, the infant larynx is more anterior and superiorly situated than that of an adult. With growth, the larynx begins to descend, resulting in vertical elongation of the pharynx and enlargement of the upper airway. The vocal cords are approximately 6 to 8 mm long in newborns, with the subglottis having a diameter between 5 and 7 mm. The trachea itself is 4 cm long and roughly 5 mm in diameter. Once the child reaches elementary school age, the vocal cords become the narrowest segment as opposed to the cricoid and remain that way into adulthood. By adulthood, the trachea is 11 to 13 cm in length and 12 to 23 mm in width. 1 Stridor develops via 3 air-fluid dynamic principles: Poiseuille law, Venturi effect, and Bernoulli principle. According to Poiseuille law, a 50% decrease in the radius of a tube results in an increase in flow resistance by 16 times, which produces a notable decrease in flow. With this change, the velocity of flow increases, known as the Venturi effect. The Bernoulli principle establishes that when flow velocity increases, the pres sure exerted by the flow decreases, resulting in the collapse of the airway. Stridor is produced by the distortions of this laminar flow and turbulence within the reduced segment of airway anatomy, resulting in the vibratory effect of tissue. 2 For example, in laryngomalacia, inspiration of air by the child produces a negative pressure of the supraglottic tissue of the larynx, resulting in further collapse and causing pathologic stridor. 3 CAUSE AND PATHOPHYSIOLOGY

DIAGNOSTIC WORKUP OF STRIDOR History

Careful attention regarding the duration and onset of the stridor is important, espe cially to differentiate a chronic symptom from an acute presentation of respiratory noise, especially if there are concomitant symptoms, such as retractions or lethargy.

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