If you think croup and stridor are basically the same, you’re not alone. Although both conditions can occur with airway obstruction, they’re different entities. The primary distinction: stridor is a sign of airway obstruction, whereas croup is a syndrome that can cause stridor. Airway obstruction, whether caused by croup or another condition, is an emergency situation that must be investigated fully and treated promptly to prevent a detrimental outcome. Your ability to identify and differentiate croup and stridor can help ensure effective treatment.
Stridor is a harsh, crowing, or vibratory sound of variable pitch that results from turbulent air flow caused by partial obstruction of the respiratory passages. Audible without a stethoscope, stridor always
warrants immediate attention because it may be the first sign of a serious or life-threatening process. (For common causes of stridor, see the box below.)
What causes stridor?
Conditions commonly associated with stridor include the following:
- Acute epiglottitis has a sudden onset. Typically, the child appears ill, drools, leans forward, and is markedly distressed. (Important: Never perform an oral examination if you suspect epiglottitis.)
- Bilateral vocal-cord paralysis produces a high-pitched inspiratory stridor. (Stridor doesn’t occur in unilateral vocal-cord paralysis.)
- Congenital subglottic stenosis causes stridor that’s commonly biphasic or inspiratory. It’s typically associated with recurrent or persistent croup. Initial signs of congenital subglottic stenosis include respiratory tract infection and edema of an already compromised airway.
- Croup (laryngotracheobronchitis) is a syndrome in which inspiratory stridor typically occurs. It’s discussed in more detail below.
- Gastroesophageal reflux disease may arise in infants with a predisposition to stridor.
- Laryngeal foreign body results from aspiration of a foreign object. It doesn’t cause fever or apparent illness.
- Laryngomalacia, the most common cause of stridor, is the inward collapse of the supraglottic structures during inspiration. Stridor associated with this condition typically is low-pitched and exacerbated by exertion. Signs and symptoms of laryngomalacia usually arise within the first 2 weeks after birth and may grow more severe over the next 6 months.
In some cases, stridor occurs only during inspiration or only during expiration; sometimes it’s biphasic, occurring during both inspiration and expiration. Inspiratory stridor, the most common type, reflects obstruction at the level of the vocal cords or higher. Expiratory stridor reflects obstruction of the small airways. (Asthma is the most common expiratory obstruction.) Biphasic stridor signifies obstruction within the subglottis or trachea.
Persistent or frequently recurring stridor usually is a harsh, medium-pitched sound heard on inspiration. Stridor and other signs of airway obstruction always warrant immediate treatment.
Also called laryngotracheobronchitis, croup is the leading cause of acute inspiratory stridor in children. Besides stridor, croup is characterized by a brassy or “barking” cough and hoarseness. The most common form of acute upper respiratory obstruction, croup in infants is a common reason for pediatric practitioner consults.
Signs and symptoms of croup stem from inflammation within the lining of the trachea and larynx, which narrows the airways and leads to negative pressure in the thoracic cavity. This negative pressure occurs distal to the narrowed area; pressure grows more negative during inspiration as the diaphragm and other inspiratory muscles try to overcome increased resistance at the obstruction level. This, in turn, causes collapse of the extrathoracic airways downstream from the obstruction, usually resulting in an audible vibration or inspiratory stridor as gas rushes through the obstruction.
Croup is most common in children ages 6 and younger. It affects about 60 of every 1,000 children between ages 1 and 2; occurrence drops significantly after age 6. Among persons diagnosed with croup, 15% have a family history of the disease; many infants and children with croup have a history of frequent respiratory infections. Conditions associated with croup include asthma, atopy (genetic hypersensitivity to environmental allergens), and diminished pulmonary function.
Croup results primarily from a viral infection (such as parainfluenza type 1 or 2 virus) in the glottis and subglottic region. Influenza type A2 virus most often necessitates airway management. Croup accompanied by wheezing commonly stems from respiratory syncytial virus, which affects the lower airways. (Children who experience croup with wheezing have an increased incidence of decreased pulmonary function.) Croup without wheezing often results from parainfluenza infections; it has no effect on the lower airways.
Croup usually is self-limiting; dyspnea and stridor typically arise as the patient starts to recover from the illness. Respiratory distress from croup varies from mild to moderate; it rarely progresses to upper airway obstruction.
Croup occurs in several types. (See the box below.)
Types of croup
Diphtheritic croup is rare in North America. Initial signs and symptoms include malaise, sore throat, low-grade fever, and anorexia. A white-gray membrane covers the entire soft palate or a portion of the tonsils. This membrane can’t be removed; forceful removal causes bleeding.
Laryngotracheitis, the most common type of croup, typically is viral and preceded by coryza (acute rhinitis) and fever.
Measles croup almost always accompanies systemic manifestation of measles and resolves as measles resolves.
Spasmodic croup is most common between ages 1 and 3—usually in children with no history of viral infection or fever. It causes a pale, watery edema. The child may have excessive saliva or may drool due to difficulty swallowing; the epithelium is intact. Spasmodic croup occurs most often at night. Its sudden onset is marked by a harsh and barking cough, noisy inspiration, respiratory distress, anxiety, and fear. It usually stems from an allergic reaction to antigens with an unknown pathology.
Viral croup, a benign and self-limiting disease, is characterized by the same barking cough and stridor that accompany other croup types. When mild, it doesn’t cause stridor or chest-wall retractions at rest.
When assessing a patient with croup, you may note hoarseness, coryza (acute rhinitis), pharyngeal erythema, and a slightly increased respiratory rate. When croup progresses to upper airway obstruction, the patient may have an increased respiratory rate, nasal flaring, and suprasternal, infrasternal, and intercostal retractions along with continuous stridor.
To aid assessment and diagnosis of croup, clinicians use the number grades below:
- Grade 1: stridor at rest without retractions.
- Grade 2: stridor and retractions of the sternal chest wall.
- Grade 3: respiratory distress, irritability, pallor or cyanosis, tachycardia, and exhaustion.
Grade 3 croup is an emergency that necessitates immediate treatment. Your ability to promptly recognize croup and stridor can save a child’s life.
Castro-Rodriguez JA, Holberg CA, Morgan WJ, et al. Relation of two different subtypes of croup before age three to wheezing, atopy, and pulmonary function during childhood: a prospective study. Pediatrics. 2001;107(3):512-8.
Hockenberry MJ, Wilson D. Wong’s Nursing Care of Infants and Children. 9th ed. Mosby; 2010.
Kliegman RM, Stanton B, St. Geme J, Schor NF, Behrman RE, Behrman RE. Nelson Textbook of Pediatrics. 19th ed. Saunders: Philadelphia, PA; 2011.
Sparrow A, Geelhoed G. Prednisolone versus dexamethasone in croup: a randomised equivalence trial. Arch Dis Child. 2006;91(7):580-3.
Tuckson RV. Clinical Evidence Handbook. London: BMJ Publishing Group; 2007.
Worrall G. Croup. Can Fam Physician. 2008;54(4):573–4. www.ncbi.nlm.nih.gov/pmc/articles/PMC2294095/
Patricia Vanderpool is a nurse practitioner in private practice in Mt. Summit, Indiana.