It is 3 am; Lily Griffen, who is 4 years old presents with difficulty breathing. She has been unwell for 2 days with an upper respiratory tract infection and fever to 38⁰C. Last night she developed a barking cough. She has awoken with noisy difficult breathing.
Vital signs: Temp 38⁰C, HR 100 bpm, RR 20min, BP 75/50, SaO₂ – 95% [room air]
Observation: Stridorous breathing with use of accessory muscles at rest.
[Note: The PDF includes a management flowchart diagram showing the approach to croup diagnosis and treatment based on severity]
Management approach based on severity:
YES: Nebulised adrenaline 0.5 ml of 1% solution in 3.5 ml saline. If no improvement or in need of further dose consult paediatric intensive care. Prednisolone 1 mg/kg orally or dexamethasone 0.6 mg/kg i.m. or orally. Close clinical monitoring. Admit to hospital.
YES: Prednisolone 1 mg/kg orally or dexamethasone 0.6 mg/kg i.m. or orally. Consider nebulised adrenaline (as above) if not improved after 30 min. Consider discharge 3 hours after initial treatment if asymptomatic.
YES: Prednisolone 1 mg/kg orally or dexamethasone 0.6 mg/kg i.m. or orally. Discharge +/- observation 1 hour if stable or earlier signs are gone. Consider admission if latest at night and/or family is geographically isolated.
YES: No specific treatment indicated. Can be discharged without further observation. Advise parents to return if there are signs of increased obstruction.
Signs of Hypoxia: agitated, distressed, cyanosis, SaO₂ \<92% in air
Severe obstruction: marked accessory muscle use/recessions
Note: Risk factors for severe disease: subglottic stenosis or other congenital or prolonged intubation; age <6 months. Down syndrome or other neurological abnormalities. Consider admission for such children even with mild symptoms.
Stridor is a harsh, high pitched noise heard predominantly during inspiration. The presence of an added respiratory sound implies an obstruction to the free flow of gas through the airway tree. Flow limitation in a compliant tube, such as the airways, is accompanied by fluttering of the walls, which occurs to conserve energy when driving pressure exceeds the pressure required to produce the maximal flow. The fluttering of the walls produces a respiratory noise. When this phenomenon occurs during inspiration, the resultant noise is known as stridor, and when it occurs during expiration, the noise is known as wheeze.
Avoid any examination that may distress the child.
Typically a disease of toddlers. Usually begins with symptoms of URTI and progresses to typical croup over 1-2 days. The typical barking cough usually begins at night or in the early hours of the morning. As the disease progresses, stridor may be heard on exertion initially. If the subglottic obstruction progresses further, stridor may be heard at rest and an expiratory component may be heard (the typical cough continues).
If the degree of obstruction continues to worsen, the stridor may become more difficult to hear and the child may become distressed and restless. Cough may be absent at this stage. The lack of stridor comes about because the amount of air moving through the obstructed airway is not sufficient to generate the noise (see above). The distress and restlessness are most likely to be due to hypoxia and signal impending complete respiratory obstruction.
The viral illness generally lasts 7-10 days, but the typical croupy cough usually only occurs on the first 2-3 nights.
Laryngomalacia, which is sometimes known as infantile larynx, is the most common cause of persistent stridor. It is not well named, as the larynx and vocal cords are actually normal. The supraglottic tissues appear as if they are too large for the size of the glottis and narrow the glottic aperture during inspiration instead of the more normal widening during inspiration. This can occur in a number of ways, the most common being:
In more severe cases combinations of these mechanisms may be responsible for the inspiratory obstruction.
Laryngomalacia classically produces a cog-wheel stridor, with no expiratory component. The cog-wheel nature to the stridor is likely to come from vibrations of the supraglottic tissues as the degree of obstruction varies during the inspiratory effort. The stridor may be worse when the infant is lying supine, although this feature is not always seen. More severe obstruction may be associated with suprasternal and sternal retraction during inspiration.
Laryngomalacia is usually a benign condition that does not require any treatment, except to reassure the parents that this is the case. Severe laryngomalacia may be associated with failure to thrive and gastro-oesophageal reflux.
Subglottic stenosis refers to a narrowing in the upper part of the trachea, immediately below the glottis. This narrowing may be congenital or acquired. Congenital subglottic stenosis occurs typically at the level of, and involves, the cricoid cartilage. The tracheal epithelium typically appears normal but the cross-sectional area of the lumen is reduced and typically does not vary with respiration. Acquired subglottic stenosis usually results from trauma and is most commonly seen in premature infants who required intubation. Older infants and children who require prolonged intubation are also at risk. Here the tracheal epithelium is more likely to be replaced by scar tissue.
Subglottic stenosis may present soon after birth or the presentation may be delayed. The stenosis, either congenital or acquired, is usually not progressive but the degree of obstruction may increase, e.g. as the child's activity levels increase or at times of respiratory infection. The typical presentation is with stridor, particularly at times of respiratory infection. If the obstruction is severe enough, the stridor may have an expiratory component and be associated with suprasternal and sternal retractions.
Many cases of subglottic stenosis do not require treatment and most will improve with growth.
Sub-glottic haemangiomas are typical haemangiomas occurring in the submucosal layer of the tracheal wall. As with other haemangiomas, they enlarge during the first year of life and typically present with increasing stridor and inspiratory obstruction. The stridor is rarely present at birth and most come to attention around 4-6 months of age. As the obstruction becomes worse, the stridor develops an expiratory component and is associated with sternal and suprasternal retractions. Approximately 50% of subglottic haemangiomas are associated with cutaneous haemangiomas, although the converse association is much less frequent.
During breathing, there are pressure gradients between the airway opening and the alveoli. Inspiration occurs when alveolar pressure is lowered below atmospheric pressure and air flows in to equalize the pressures. At the onset of expiration, alveolar pressure exceeds atmospheric pressure and air flows out.
There are also pressure gradients across the airway wall and these tend to alter airway calibre. The pressure around the extrathoracic airways, that is, those above the thoracic inlet, is atmospheric, while the pressure around the intrathoracic airways essentially is equal to the pleural pressure. The pressure gradients across the airway wall during inspiration means that there is a net force tending to narrow the extrathoracic airways and to dilate the intrathoracic airways. During expiration, the direction of the forces is opposite, resulting in a tendency to narrow intrathoracic airways and dilate extrathoracic airways.
As stridor is an inspiratory noise, the predominant site of obstruction (the site responsible for the flow limitation) is generally in the extrathoracic airways. Stridor with an expiratory component, that is, where the noise can also be heard at the beginning of expiration, can result from either a severe obstruction producing flow limitation during expiration as well, or from a lesion that extends into the intrathoracic airways.
Figure: The distribution of pressures throughout the respiratory system during (A) inspiration and (B) expiration. Atmospheric pressure is shown as zero. During inspiration, the expansion of the thorax results in pleural pressure falling below atmospheric. This relatively negative pressure is transmitted to the alveoli and a pressure gradient is established between the airway opening and the alveoli. Gas flows into the lungs along this pressure gradient. The pressure outside the airways is essentially pleural pressure and results in net forces that tend to expand intrathoracic airways and to collapse the extrathoracic trachea. As shown in B, the pressure gradients are opposite during expiration.
There is a widespread belief that exposing these children to steam, especially by steaming up the home bathroom, helps relieve stridor. There is no evidence to support this treatment. The only benefit that is likely to come from sitting with the child in a steamy bathroom is from sitting quietly with the child and not from the steam.
Some children suffer recurrent episodes of croup, frequently without the preceding viral prodrome usually seen in acute viral croup. Typically these children are well when they go to bed and wake in the early hours of the morning with a barking cough and stridor. Fever is unusual in this form of croup. The same viruses as found in acute viral croup may be found in the upper airways of children with spasmodic croup, although the relationship between the viruses and the symptoms is less clear. Frequently children with recurrent croup have a family history of atopy and asthma or have asthma themselves. This, together with the uncertain relationship between the clinical symptoms and the presence of a virus, have led to the concept that spasmodic croup maybe a manifestation of upper airway hyper responsiveness. There are no direct data to support or refute this hypothesis.