Abstract
This chapter discusses the common and potentially serious infective causes of acute upper airway obstruction in children. The laryngeal anatomy of young children makes them particularly susceptible to upper airway obstruction, and during acute infections this is exacerbated by inflammation and edema of the airway mucosa. The most common cause of infective upper airway obstruction in children is viral laryngotracheobronchitis, or croup, which is usually a mild and self-limiting illness, but management with corticosteroids may still be necessary. Bacterial causes of upper airway obstruction have fortunately become rare since the introduction of the Haemophilus influenzae B (HiB) immunization, but a few cases of epiglottitis do still occur due to nonimmunization, vaccine failure, and infection with non-HiB organisms. These cases constitute a medical emergency due to the risk of rapid progression to complete airway obstruction. Other rare conditions are discussed including bacterial tracheitis, diphtheria, retropharyngeal, and peritonsillar abscesses. Key learning points in this chapter include the main discriminating factors of the various causes of infective upper airway obstruction, the importance of a calm and minimally distressing approach to the child presenting with stridor, and the need for early anesthetic team involvement in cases with a suspected bacterial etiology or signs of impending airway obstruction.
Keywords
upper respiratory tract infection, upper airway obstruction, croup, viral laryngotracheobronchitis, epiglottitis, bacterial tracheitis
Upper airway obstruction due to acute infection is not uncommon in children, and many parents have experienced an anxious night with a “croupy” child. Although infants and young children are most commonly affected because they have relatively narrow upper airways, older children and adults can also have significant symptoms. Fortunately, these are mostly due to self-limiting viral laryngotracheobronchitis (LTB), but there is also a group of bacterial infections (e.g., epiglottitis, bacterial tracheitis, diphtheria, retropharyngeal abscess, and peritonsillar abscess) that can occasionally cause significant obstruction. It is the job of the emergency physician, pediatrician, pediatric pulmonologist, or otorhinolaryngologist to diagnose more serious infections promptly so that treatment can be instituted early and disastrous obstruction avoided. It is also important to recognize when a simple viral LTB is causing significant problems, so that appropriate treatment can be given immediately. This chapter is clinically oriented and outlines the principal infective causes of upper airway obstruction, with an emphasis on diagnosis and treatment. Confusion exists regarding the nomenclature for these disorders, with some using the term croup to refer to any inflammatory disorder of the upper airway, whereas others restrict its use to subglottic disease (i.e., LTB, which is usually of viral origin). Therefore, for the sake of clarity, the term croup will be largely avoided in this chapter.
The consequence of these upper airway infections is usually stridor, which is a clinical sign and should not be considered a definitive diagnosis. This section briefly outlines the principles behind what causes stridor, which should clarify why this condition mostly affects infants and young children. The appendix in Holinger and colleagues’ Pediatric Laryngology and Bronchoesophagology discusses the physics of air flow and fluid dynamics. The laws of fluid dynamics are based on flow through fixed tubes and may not always apply to dynamic airways in vivo. Normally, air flow through the upper airways is laminar, and the moving column of air produces slight negative pressure on the airway walls. Inflammation resulting from infection causes a degree of airway narrowing, which increases the flow rate through the narrowed segment (the Venturi effect). This, in turn, causes a reduction in the pressure exerted on the airway wall. This is the Bernoulli principle. In other words, negative intraluminal pressure increases. This enhances the tendency of the airway to collapse inward, further narrowing the airway and causing turbulent air flow. The respiratory phase (inspiration or expiration) has a differential effect on air flow, depending on whether the obstruction is intrathoracic or extrathoracic ( Fig. 23.1 ). Stridor is the sound made by rapid, turbulent flow of air through a narrowed segment of a large airway. It is most often loud, with medium or low pitch, and inspiratory. It usually originates from the larynx, upper trachea, or hypopharynx. Progression of the disease process may make stridor softer, higher-pitched, and biphasic (inspiratory and expiratory). With the onset of complete obstruction, stridor may become barely audible as minimal air moves through the critically narrowed airway.
The laryngeal anatomy of children makes them particularly susceptible to narrowing of the upper airways. The larynx of a neonate is situated high in the neck, and the epiglottis is narrow, omega-shaped (ω), and vertically positioned. The narrowest segment of the pediatric airway is the subglottic region (in adults, it is at the glottic level), which is encircled by the rigid cricoid cartilage ring. There is nonfibrous, loosely attached mucosa in this region that is easily obstructed in the presence of subglottic edema. In addition, the cartilaginous support of the infant airway is soft and compliant, easily allowing dynamic collapse of the airways during inspiration. Young children have proportionally large heads and relatively lax neck support; this combination increases the likelihood of airway obstruction when supine. Also, their tongues are relatively large for the size of the oropharynx. Simple mathematics shows why a small amount of edema has such a profound effect on the cross-sectional area and hence air flow. The diameter of the subglottis in a normal newborn is approximately 5 mm, and 0.5-mm edema in this region reduces the cross-sectional area to 64% of normal (area = π ∞ radius ). Air flow is directly proportional to the airway radius to the fourth power (Poiseuille’s law), so a small reduction in caliber has a major effect on flow rate. The same 5-mm airway with 0.5 mm edema will have a flow rate of only 41% of baseline, assuming that pressure remains unchanged—a situation that is not necessarily the case if the Bernoulli principle is in play. Because the caliber of the airway is almost inevitably reduced further in accord with the Bernoulli principle, and Poiseuille flow is not established, the flow rate is much further reduced, and the work of breathing is greatly increased to maintain ventilation.
Viral Laryngotracheobronchitis
Epidemiology
Viral LTB is the most common cause of infective upper airway obstruction in the pediatric age group. Affected children are usually of preschool age, with a peak incidence between 18 and 24 months of age. Although viral LTB episodes become uncommon beyond 6 years of age, cases have been reported during later childhood and adolescence, and rarely described in adults. Reported annual incidence rates in preschool children vary from 1.5% to 6%, but less than 5% of these require hospital admission, and only 1% to 2% of those admitted require endotracheal intubation and intensive care. This proportion has fallen dramatically since the use of corticosteroids has become routine. Mortality is low, reported by one 10-year follow-up study as less than 0.5% of intubated patients. There is a male preponderance in children younger than 6 years of age (1.4 : 1), although both sexes appear to be affected equally at an older age.
Children with a specific CD14 genetic polymorphism (C/C variant of CD14 C-159T) have recently been described as having a reduced prevalence of croup. It has been hypothesized that this relates to the role of the CD14 gene as a pattern recognition receptor in the mediation of the innate immune system response to LTB-causing viruses.
Cases may occur in epidemics, with those caused by parainfluenza virus (PIV) type 1 typically presenting in fall and winter months. Infections caused by other common organisms, including other PIV subtypes, occur more commonly as isolated infections. Infection is via droplet spread or direct inoculation from the hands. Viruses can survive for long periods on dry surfaces, such as clothes and toys, emphasizing the importance of infection-control practices.
Etiology
The most common etiologic agents are the PIVs, of which PIV 1 is found most frequently and leads to epidemics. PIV 2 may account for many sporadic cases, and PIV 3 is a less common cause of viral LTB, usually targeting the epithelium of the smaller airways and leading to bronchiolitic illness. Less is known about the clinical presentation of PIV 4, but it is reported to result in milder clinical illness and is infrequently associated with croup symptoms. The PIVs belong to the Paramyxoviridae family, along with respiratory syncytial virus, measles, mumps, and the recently identified human metapneumovirus. Together the PIVs account for more than 75% of viral LTB cases, although other respiratory viruses (e.g., respiratory syncytial virus, rhinovirus, adenovirus, coronavirus, human bocavirus, and enteroviruses) can produce a similar clinical syndrome. Herpes viruses and influenza viruses tend to cause a more severe and protracted form of the disease. LTB can also occur with some systemic infections, such as measles and, less commonly, mycoplasma. In general, however, it is not usually possible to identify the cause of infection from the child’s symptoms because severity does not correlate with any particular etiologic agent.
Pathology
Infection affects the larynx, trachea, and bronchi, although swelling and inflammation in the subglottic area leads to the characteristic clinical features of viral LTB. In addition to relative differences in airway size (discussed earlier in the chapter), it is suggested that poor cell-mediated immunity in younger age groups also accounts for differences observed between adults and children. The epithelium of the subglottis possesses abundant mucous glands, secretions from which can further narrow the airway lumen in response to infection. The PIVs are trophic for the respiratory epithelium, binding in particular to ciliated cells via an interaction between the viral hemagglutinin-neuraminidase protein and its receptor, sialic acid. Other viral proteins (the F protein in particular) are important in membrane fusion and the passage of viral particles between cells. Many strains of PIV are cytopathic, with infection leading to the formation of giant cells and cell death. As with many infective processes, the ensuing inflammatory response is involved in the evolution of symptoms. Both polymorphonuclear and monocytic leukocytes infiltrate the subepithelium, which leads to vascular congestion and airway wall edema. In addition, the symptoms of viral LTB are believed to be caused by the release of spasmogenic mediators, leading to decreased airway diameter. This may result from a type I hypersensitivity response to PIV, and some authors have postulated a role for anti-PIV-specific immunoglobulin E (IgE) in the development of airway narrowing. These factors may play a relatively greater role in patients with recurrent (spasmodic) croup, and these patients may have hyperreactivity of the extrathoracic and intrathoracic airways.
The etiology of recurrent, spasmodic croup remains unclear, with authors expressing differing views on whether it is usually virus-related or is a separate disease entity; suggested triggers include gastroesophageal reflux, eosinophilic esophagitis, and anatomical abnormalities, in addition to an allergic predisposition.
Clinical Features
Mild
Most children are affected mildly by viruses that cause LTB. The exact incidence remains unknown, because many of them do not receive medical attention, but are managed by parents at home. Children have a barking cough and a hoarse cry or voice; these symptoms are worse in the evening and at night. They may also have inspiratory stridor on exertion, but stridor at rest is usually absent, as are other signs of respiratory distress. There is most commonly a coryzal prodrome accompanied by a low-grade fever, but children are not particularly unwell or toxic. They remain interested in their surroundings, are playful, and still eat and drink.
Moderate
Features of moderate viral LTB include those discussed earlier, but with inspiratory stridor present at rest, as well as a degree of respiratory distress manifest by chest wall recession, tachypnea, and the use of accessory muscles of respiration. There is usually accompanying tachycardia, but children remain interactive and are able to take at least liquids orally.
Severe
Progression from moderate to severe infection can occur rapidly and may be precipitated by the distress caused by clinical examination. Worrisome signs include those of increasing respiratory distress, with the child appearing anxious or preoccupied and tired. Drooling may occur (but not as commonly as in epiglottitis), and the child will often refuse liquids or be unable to coordinate swallowing and breathing. However, the child with viral LTB will not appear toxic, with high fever and flushed face, as do those with the classic signs of bacterial epiglottitis ( Table 23.1 ). Another difference is in the nature of the cough; a harsh, barking cough is not commonly associated with epiglottitis (in which there is often a muffled cough and cry). Restlessness and agitation are late signs of airway obstruction of any cause, as is cyanosis, pallor, or decreased level of consciousness. Pulse oximetry should be performed, but limitations must be recognized. Oxygen saturation may be well preserved until the late stages of severe viral LTB, and it can lead to significant underestimation of respiratory compromise in a patient who is receiving supplementary oxygen. Conversely, desaturation may be seen in children with relatively mild airway obstruction (presumably reflecting lower airway involvement and ventilation-perfusion mismatch). Pulsus paradoxus is present in the group with severe disease, but in clinical practice, it is difficult to assess, and attempts to do so could worsen symptoms by causing distress.
| Viral Laryngotracheobronchitis | Epiglottitis | Bacterial Tracheitis | Diphtheria | Retropharyngeal Abscess | |
|---|---|---|---|---|---|
| Principal organisms | Parainfluenza 1–3 Adenovirus respiratory syncytial virus | Haemophilus influenzae, Streptococcus | Staphylococcus aureus, Moraxella catarrhalis, H. influenzae | Corynebacterium diphtheria | Mixed flora, including S. aureus, Streptococcus, H. influenzae, anaerobes |
| Age range | 6 months–4 years (peak, 1–2 years) | 2–7 years | 6 months–8 years | All ages | <6 years |
| Incidence | Common | Rare | Rare | Rare if vaccinated | Uncommon |
| Onset | Insidious usually follows upper respiratory tract infection | Rapid | Slow, with sudden deterioration | Insidious | Gradual |
| Site | Below the vocal cords | Supraglottis | Trachea | Tonsils, pharynx, larynx, nose, skin | Retropharyngeal space |
| Clinical manifestations | Low-grade fever Nontoxic barking (seallike) cough Stridor hoarseness Restlessness | High fever Severe sore throat Minimal nonbarking cough Toxic stridor Drooling Dysphagia Muffled voice Tripod position | High fever Toxic, brassy cough Stridor Hoarse voice Neck pain Choking | Fever Toxic stridor Sore throat Fetor oris Cervical lymphadenopathy Bull neck | Fever Sore throat Neck pain and stiffness (especially on extension) Dysphagia Stridor (less common) Drooling Retropharyngeal bulge |
| Endoscopic findings | Deep red mucosa Subglottic edema | Cherry-red or pale and edematous epiglottis Edematous aryepiglottic folds | Deep red mucosa Ulcerations Copious, thick tracheal secretions Subglottic edema, with normal epiglottis and arytenoids | Gray, adherent membrane on the pharynx | N/A |
| Intubation | Occasional | Usual | Usual | Occasional | Unusual |
| Therapy | Corticosteroids Nebulized epinephrine | Intubation (1–3 days) IV antibiotics | Intubation (3–7 days) IV antibiotics Tracheal suction | Diphtheria antitoxin IV antibiotics Immunization during convalescence | IV antibiotics ± surgery |
Diagnosis and Differential Diagnosis
The diagnosis of croup is made clinically, based on the features described earlier; there is no role for laboratory tests or radiography in the assessment of acute airways obstruction. In skilled hands, plain lateral neck radiographs may demonstrate sites of obstruction, but this rarely influences management; it also wastes time and can be dangerous. The neck extension that is required could precipitate sudden worsening of airway obstruction, which can be fatal in severe cases. Investigations during the acute illness should be reserved for children with an atypical presentation or who fail to respond to conventional treatment. In such cases, alternative infective (e.g., epiglottitis) and noninfective (e.g., inhaled foreign body) causes of acute airway obstruction require careful exclusion (see Box 23.1 and Table 23.1 ). Advice from a senior clinician is vital when croup is severe.
Recurrent or Spasmodic Croup
Symptoms are similar to those of the more typical forms of viral LTB, but children are often older, do not have the same coryzal prodrome, and may be afebrile during the episode. There may be links with atopy, often with a positive family history. Episodes are often similar to acute asthma except the child has stridor rather than wheeze. Attacks often occur suddenly, at night, and may resolve equally quickly. Treatment must be guided by the degree of severity, and is similar to that for viral LTB. Some practitioners prescribe oral or inhaled corticosteroids (via a nebulizer) to be kept at home and administered by the parents in case of an episode, although there is a paucity of evidence for or against this practice in spasmodic croup.
Noninfective Causes of Acute Airway Obstruction
There are a number of noninfective causes of upper airway obstruction, and these must be considered in the differential diagnosis of infective causes (see Box 23.1 ). Foreign body inhalation is the most common noninfective cause in children. Symptoms may partly mimic those of viral LTB and will depend on the location of the foreign body, the degree of resultant airway obstruction, and (to a lesser extent) the nature of the foreign body. Onset of symptoms may be either acute or insidious; a large foreign body may cause severe obstruction, whereas a smaller one may simply lead to laryngeal and tracheal irritation and airway edema. In cases of severe airway obstruction, the voice may be lost and breath sounds quiet. This condition is an emergency, and requires immediate visualization of the larynx and trachea and removal of the foreign body by a physician or surgeon experienced in this procedure. Occasionally an unrecognized inhaled foreign body leads to chronic stridor. Acute upper airway obstruction may also result from the ingestion of caustic substances, with resulting pharyngeal burns, edema, and inflammation of the epiglottis, aryepiglottic folds, larynx, and trachea. This diagnosis is usually clear from the history. Rarely, angioneurotic edema may cause acute laryngeal swelling and airway obstruction. Patients appear nontoxic and may exhibit other signs of allergic disease, such as urticaria and abdominal pain. In hereditary angioneurotic edema due to C1 esterase inhibitor deficiency, the family history may be positive, although the first presentation is more common in adults than in children. Hypocalcemia, for example, due to hypoparathyroidism, can lead to laryngospasm (a form of tetany), which can cause stridor with significant airway obstruction.
There are numerous causes of chronic airway obstruction that are discussed elsewhere in this book. Confusion may arise when an upper respiratory tract infection unmasks a previously asymptomatic congenital abnormality. For example, mild subglottic stenosis may cause symptoms only with the additional burden of airway edema due to a simple viral upper respiratory infection. It is important to ensure that there is no history of intubation (which may have been brief, as in resuscitation of a newborn in the maternity unit) or of any coexisting signs (e.g., a cutaneous hemangioma) that may increase the index of suspicion for a congenital airway abnormality. One catch with subglottic hemangiomata is that they may initially respond to systemic steroids, and thus their diagnosis may be masked with the assumption that stridor was due to viral croup.
Management of Viral Laryngotracheobronchitis
Management of viral LTB must be based on clinical assessment of severity. Several scoring systems have been devised, and the most commonly applied system (the 17-point Westley scale, which assesses degree of stridor, chest retractions, air entry, cyanosis, and level of consciousness) has been well validated. However, these are mainly used in the context of clinical trials and are not a substitute for experienced clinical assessment.
Supportive Care
Children with mild croup can be managed at home. They should be treated with plenty of fluids and antipyretics as required. Because the vast majority of cases are of viral etiology, there is no role for the routine use of antibiotics in the absence of other features suggestive of bacterial infection. Parents should be warned that symptoms are usually worse at night and may recur after apparently disappearing during the day.
Humidification
Both at home and in the hospital setting, humidified air (either steam or cool mist) has been used for more than a century to produce symptomatic relief from croup. Despite this, there is very little supportive evidence; most early studies, some of which may have been underpowered, generally suggested no benefit. A larger study of 140 moderately affected children showed no differences in signs or requirement for additional treatments with optimally delivered 100% humidity, and the most recent Cochrane Systematic Review has also concluded there is no evidence of benefit. Case reports have described severe burns caused by spilling of boiling water and facial scalds from the use of steam, so this type of treatment is not without the potential for harm.
Corticosteroids
The use of corticosteroids has received much attention for more than a decade, and their therapeutic role is well established. Their mechanism of action, however, remains unclear, although is believed to relate to rapid-onset antiinflammatory properties. The cumulative evidence strongly supports their use in children with moderate to severe symptoms, although there are still outstanding questions, including the optimal route of administration, the most appropriate dosing regimen, and the best oral agent.
The role of corticosteroids in the management of croup in children has been the subject of several Cochrane reviews, with the most recent update in January 2011. In this review, the authors identified 38 studies that fulfilled their criteria for inclusion—namely, randomized controlled trials in children measuring the effectiveness of corticosteroids (any route of administration) against either a placebo or another treatment. A total of 4299 children were included, the majority from double-blind, placebo-controlled trials. Outcome measures included the croup score (most commonly the Westley scale), the requirement for admission or return visit, the length of stay, the requirement for additional therapeutic interventions, and overall assessment of “improvement” (indicated by a minimum incremental improvement in croup score or subjective relief of symptoms). Overall, treatment led to an improvement in the croup score at 6 and 12 hours, with a number needed to treat (NNT) of 5 calculated in order to achieve clinical improvement in one child at both those time points. The improvement was no longer apparent at 24 hours, but this was thought to be a reflection of reduced statistical power due to the small number of participants evaluated at 24 hours. The length of time spent in either the emergency department or the hospital was also significantly decreased, as was the requirement for nebulized epinephrine. Importantly, and in contrast to the first version of this Cochrane review, the authors concluded with funnel plots and other statistical methods that these results were not influenced by publication bias. In conclusion, there is convincing evidence that corticosteroids provide effective and sustained treatment of croup symptoms, leading to clinical improvement within 6 hours of administration. In severe disease, rates of intubation are significantly decreased and the duration of intubation is reduced, and in moderate disease admission, the need for additional treatment and return visits are reduced. More recent studies have focused attention on the optimal formulation, dose, and treatment regimen.
Optimal Route of Administration, Formulation, and Dosing Regimen
Studies included in the Cochrane review (discussed earlier in the chapter) and others conducted since then have used the intramuscular, oral, or nebulized route to administer different corticosteroid preparations. This area has been well reviewed recently. From the studies that have attempted to address the route of administration, nebulized, oral, and intramuscular routes appear, in general, to be roughly equivalent. Nebulization could potentially increase distress of the child and worsen upper airway obstruction, although it may be preferable in a child who is vomiting or having difficulty swallowing.
Similarly, studies using oral agents have used either dexamethasone or prednisolone, and both in varying doses. Many primary care physicians who visit homes do not routinely carry dexamethasone but do carry oral prednisolone. There is no strong evidence in support of one preparation over the other, although one recent study favored dexamethasone, which led to a reduced frequency of re-presentation. In contrast, a recent Australian trial compared 1 mg/kg prednisolone with a single dose of oral dexamethasone using two different dosing regimens (0.15 and 0.6 mg/kg) and found no difference in croup score, requirement for further treatment, or re-presentation. Similarly, a community-based double-blind trial comparing a single dose of dexamethasone 0.6 mg/kg with three doses of 2 mg/kg prednisolone on consecutive days found no difference in additional health care attendances, duration of symptoms, parental stress, or sleep disturbance. With regard to dexamethasone, 0.6 mg/kg has been the dose most widely used, but several studies have demonstrated that this dose may be higher than required and that 0.15 mg/kg is just as effective. A practical approach might be to use dexamethasone, if available, at a dose of 0.15 mg/kg. If this preparation were not available at a home visit, prednisolone (at an equivalent dose of 1 mg/kg) could provide a useful substitute. Due to the short duration of symptoms in a typically episode of croup, one dose of steroid is usually sufficient treatment. However, a second dose should be considered if residual symptoms are still present the following day, and can be given to the parents to administer at their discretion.
Nebulized Epinephrine (Adrenaline).
The most recent update of the Cochrane Review of nebulized epinephrine use in croup was published in 2013. It included eight randomized controlled studies, with a total of 225 subjects comparing the efficacy of nebulized epinephrine to placebo (six studies), or comparing different epinephrine formulations and delivery methods (two studies).
All studies involved the management of moderate to severe croup in either an emergency department or hospital setting. Outcome measures used were croup score, intubation rates, side effect profile, and total health care utilization. Nebulized epinephrine was associated with improved clinical severity score 30 minutes posttreatment, but this effect was not sustained at 2 or 6 hours posttreatment. Magnitude of benefit was consistent between studies, and similar, irrespective of whether epinephrine was administered in an inpatient or outpatient setting.
Duration of hospitalization was also significantly reduced with epinephrine (mean difference of 32 hours), although this outcome was only assessed in one study. No studies provided a comparison of intubation rate or side effect profile. In summary, nebulized epinephrine has been shown to improve clinical severity in the short term and reduce hospital admission in cases of moderate to severe croup. It should be used in any child who has severe signs and symptoms, and it should be considered for those with moderate signs and symptoms, depending on the signs of respiratory distress and possible response to corticosteroid administration. It can be administered in the home setting while awaiting an ambulance, but clearly any child requiring this treatment at home must be transferred promptly to the hospital for monitoring. Multiple doses may be administered, although the requirement for this must lead to consideration of the need for intensive care management. Although rebound worsening of symptoms after administration of nebulized epinephrine is often alluded to, in practice, this phenomenon does not appear to be a real risk. Traditionally, children treated with epinephrine have been admitted to the hospital, but recent studies have confirmed that discharge home is safe after 3 to 4 hours of observation if the child has made significant improvement.
Most clinical trials have used the racemic form of this drug, although there is evidence that the l -isomer used alone (which is the only available formulation in some units) may be equally effective and has a longer duration of action. The mechanisms of action are believed to be a combination of rapid reduction in airway wall edema and bronchodilation. The recommended dose is 0.4 to 0.5 mL/kg (to a maximum of 5 mL) of the 1 : 1000 preparation that is put undiluted into the nebulizer cup. Intramuscular epinephrine is not used in severe stridor, so it is important to ensure the stridor is not due to acute anaphylaxis, in which case it should be given.
Other Treatments for Severe Cases.
Oxygen should be administered to any child with severe airway obstruction, even in the absence of severe hypoxia, because it will aid respiratory muscle function. As mentioned earlier, a child with severe respiratory distress and obstruction may have normal pulse oximetry readings when breathing oxygen, which can be dangerous if misinterpreted by staff who are unaware of this limitation. Heliox (70% to 80% helium with 20% to 30% oxygen) has been used in both upper airway obstruction and severe asthma, and it is the focus of a recent Cochrane review.
Three randomized controlled trials were identified totaling 91 participants with croup of varying severity. Heliox was compared with either 30% humidified oxygen, 100% oxygen plus epinephrine, or against no treatment. No pooled analysis was possible, as each study used a different comparator. Collectively, these studies provided evidence of a short-term benefit of Heliox inhalation, with improved croup scores at 60 to 90 minutes following administration. However, this clinical improvement was not sustained over subsequent hours. The authors summarized that no additional benefit appeared to have been provided by Heliox beyond that delivered by administration of 30% oxygen in cases of mild croup, or 100% oxygen plus nebulized epinephrine in moderate to severe croup. Adequately powered studies are required to further evaluate the role of Heliox in the management of moderate to severe croup.
Endotracheal Intubation
Some children with severe croup either do not respond to the usual therapies or are too severely compromised at presentation to permit their use. These children require urgent endotracheal intubation and mechanical ventilation to avoid potentially catastrophic complete airway obstruction and the serious sequelae of hypoxia and hypercapnia (e.g., hypoxic ischemic encephalopathy). Intubation should be performed by the most experienced person available, and it should be attempted with an uncuffed endotracheal tube one size smaller than the usual size for the child. Facilities for immediate tracheostomy must be available at the time of intubation. Children may have coexisting lower airway and parenchymal involvement that impairs gas exchange and may lead to slower than expected clinical improvement after intubation. Rarely, pulmonary edema may develop after relief of airway obstruction, particularly if the disease course has been prolonged. Most children without severe parenchymal involvement require respiratory support for 3 to 5 days. This is one context in which multiple rather than single doses of corticosteroids are often administered. The timing of extubation will depend on the development of an air leak around the endotracheal tube, indicating resolution of airway narrowing. Reintubation rates of approximately 10% have been reported.
Prevention
Because of the substantial health care costs associated with management of PIV infections (estimated annual costs of $43, $58, and $158 million for hospitalizations in the United States for PIV-associated bronchiolitis, croup, and pneumonia, respectively), there is much interest in development of an effective PIV vaccine. The most promising candidate vaccine developed to date is an intranasally administered cold-adapted PIV 3 vaccine that appears to be well-tolerated and immunogenic in infants as young as 1 month of age. Also under evaluation is a PIV3-vectored RSV vaccine that would confer protection against both of these common respiratory viruses. Results from efficacy studies into each of these promising vaccine candidates are awaited.
Prognosis and Further Evaluation
Most children with viral LTB were previously well, have short, self-limiting symptoms, and make a full recovery. The lack of complete immunity and the variety of agents that can cause viral LTB mean that more than one episode is not uncommon, particularly in separate seasons.
Recurrent (≥3) episodes have been reported in more than 60% of affected children, with family history of croup identified as the most significant risk factor for recurrence in one case-control study. Although further evaluation is not necessary in every case of recurrent croup, it should be considered in cases that are particularly severe or frequent, if symptoms are particularly slow to resolve, or if symptoms occur between or in the absence of obvious infections. Evaluation of patients in this group is aimed at identifying an underlying airway abnormality that would predispose the child to more severe airway narrowing with viral infections, or that could cause problems independently of such infection. Investigation is usually centered on airway endoscopy. This must be performed in a unit and by an operator who is experienced in the technique because there is a risk of exacerbating the airway obstruction. Spontaneous breathing is necessary to identify vocal cord problems or airway malacia, and anesthetic techniques must be carefully considered. If an inhaled foreign body is considered likely, rigid bronchoscopy is the study of choice. Additional studies that might be considered once the acute episode has resolved include plain lateral neck and chest radiographs, computed tomography or magnetic resonance imaging, contrast assessment of the upper airway (e.g., videofluoroscopy, barium swallow), and a pH probe study. Polysomnography may help determine the severity of chronic symptoms. Rarer causes of recurrent stridor (e.g., hypocalcaemia or angioneurotic edema) are diagnosed by blood testing.
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