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Stridor

What is stridor?

Stridor is a high-pitched sound that is usually heard when a child breathes in (inspiration). It is usually caused by an obstruction or narrowing in your child's upper airway. The upper airway consists of the following structures in the upper respiratory system:

• Nose
• Mouth
• Throat (pharynx and larynx)
• Pharynx - is the muscle-lined space that connects the nose and mouth to the larynx and esophagus (eating tube)
• Larynx - also known as the voice box, the larynx is a cylindrical grouping of cartilage, muscles and soft tissue which contains the vocal cords. The larynx is the upper opening into the windpipe (trachea), the passageway to the lungs. The Subglottic space is immediately below the vocal cords. It is the narrowest part of the upper airway. The epiglottis is a flap of soft tissue and cartilage that folds over the vocal cords to prevent food and irritants from entering the lungs.
• Trachea (windpipe) - a tube that extends from the voice box to the bronchi in the lungs.

The sound of stridor depends on location of the obstruction in the upper respiratory tract. Sometimes, the stridor is heard when the child breathes in (inspiration) and can also be heard when the child breathes out (expiration).

What are the causes of stridor?

There are many different causes of stridor. Some of the causes are diseases, while others are problems with the anatomical structure of the child's airway. The upper airway in children is narrower than that of an adult and therefore more susceptible to problems with obstruction.

The following are some of the more common causes of stridor in children:

Congenital causes (problems present at birth)

• Laryngomalacia - Parts of the larynx (voice box) are floppy and collapse causing partial airway obstruction. The child will usually outgrow this condition by the time he or she is 18 months old. In rare instances, some children may need surgery.
• Subglottic stenosis - The subglottis is the space in the larynx (voice box) right below the vocal cords. If the area is too small, this is referred to as subglottic stenosis. A child can be born with this problem (congenital subglottic stenosis) or it can result from trauma such as prolonged tracheal intubation - placing a tube into the trachea, "windpipe", (acquired subglottic stenosis). Subglottic stenosis can prevent adequate movement of air into the child’s lungs and cause stridor. Symptoms often worsen with upper respiratory infection or colds. The child may outgrow mild subglottic stenosis, but more severe cases will require surgical intervention.
• Subglottic hemangioma - A hemangioma is a mass made of blood vessels; it is similar to a strawberry birthmark or “stork bite.” Hemangiomas usually grow rapidly for 6 – 12 months and then shrink. If a hemangioma in the subglottic space causes airway obstruction, the child may need medical and/or surgical treatment.
• Vascular rings - The trachea, or windpipe, may be compressed by an artery inside the chest. Surgery may be required to alleviate this condition.  

Infectious causes

• Croup - Croup is an infection caused by a virus that leads to swelling in the subglottic space (the area below the vocal cords.) It causes breathing problems. Croup is caused by a variety of different viruses, most commonly the parainfluenza virus. Treatment includes breathing humidified air and the occasional use of oral steroids.
• Epiglottitis - Epiglottitis is an acute life-threatening bacterial infection that results in swelling and inflammation of the epiglottis. (The epiglottis is an elastic cartilage structure at the back of the tongue that helps to prevent food from entering the windpipe when swallowing.) This causes breathing problems that can progressively worsen and may, ultimately, lead to airway obstruction. There is so much swelling that air cannot get in or out of the lungs, resulting in a medical emergency. Epiglottitis is usually caused by the bacteria Haemophilus influenzae, and now is rare because children are routinely vaccinated against this bacteria.
• Bronchitis - Bronchitis is an inflammation of the breathing tubes (airways), called bronchi, that causes increased production of mucus and other changes. Acute bronchitis is usually caused by infectious agents such as bacteria or viruses. It may also be caused by physical or chemical agents—dusts, allergens, strong fumes—and those from chemical cleaning compounds or tobacco smoke.
• Severe tonsillitis - The tonsils are small, oval pieces of tissue that are located in the back of the mouth on the side of the throat. Tonsils help fight infections by producing antibodies. Tonsillitis is an inflammation of the tonsils. When the inflamed tonsils get very large, airway obstruction can occur.
• Abscess in the throat - An abscess in the throat is a collection of pus surrounded by inflamed tissue. If the abscess is large enough, it may narrow the airway to a critically small opening. These abscesses may occur next to the tonsil or in the soft tissue of the neck surrounding the airway.

Traumatic causes

• Foreign bodies - Foreign bodies in the breathing tract may cause severe airway symptoms. Foreign bodies are any objects placed in the mouth that do not belong there. For example, a peanut in the trachea (windpipe) may close off the breathing passages and result in suffocation and death.

Other causes

• Trauma (injury) to the neck - Trauma to the neck may cause a fracture to the larynx or bleeding into the airway.
• Swallowing a harmful substance - Swallowing a harmful substance (acid, lye)

How is stridor diagnosed?

Stridor is usually diagnosed relying on the medical history and physical examination of your child. It is important to remember that stridor is a symptom of some underlying problem or condition. If your child has stridor, your child's physician may order some of the following tests to help determine the cause of the stridor:

• Blood tests
• X-ray of the chest and/or neck
• Pulse oximetry - an oximeter is a small machine that measures the amount of oxygen in the blood. To obtain this measurement, a small sensor (like an adhesive bandage) is taped onto a finger or toe. When the machine is on, a small red light can be seen in the sensor. The sensor is painless and the red light does not get hot.
• Culture - Sputum culture is a diagnostic test performed on the material that is coughed up from the lungs and into the mouth. A sputum culture is often performed to determine if an infection is present. A nose of throat culture may also be obtained.
• Endoscopic evaluation of the airway – Visualization of the upper airway that is obtained by inserting a small, flexible, lighted instrument into the child’s nose to examine the nose, pharynx and larynx. Topical anesthesia may be required for this procedure.

The specific treatment for this condition depends on many factors and is tailored for each child. Please discuss your child's condition, treatment options and your preferences with your child's physician or healthcare provider.

Treatment may include:

• Referral to an ear, nose and throat specialist (otolaryngologist) for further evaluation (if your child has a history of stridor)
• Surgery
• Medications by mouth or injection (to help decrease the swelling in the airways)
• Hospitalization and emergency surgery may be necessary depending on the severity of the stridor.

Reviewed by: Steven D. Handler, MD, MBE
Date: April 2009