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Evaluation of the upper airway
PAEDIATRIC RESPIRATORY REVIEWS (2004) 5, 9–16 doi:10.1016/j.prrv.2003.09.006
MINI-SYMPOSIUM: UPPER AIRWAY OBSTRUCTION
Evaluation of the upper airway Ernst Eber Respiratory and Allergic Disease Division, Paediatric Department, University of Graz, Austria KEYWORDS children; endoscopy; imaging; infants; pulmonary function testing; upper airway obstruction
Summary The evaluation of infants and children with upper airway obstruction always involves a history and physical examination, which in many cases allow a diagnosis to be made. Assessment of severity and response to treatment relies on subjective parameters. Flow-volume loop analysis is a rapid, simple and effective method of evaluating patients with upper airway obstruction non-invasively. Imaging studies are complementary to endoscopy, and include plain radiography as well as computed tomography and magnetic resonance imaging, with the latter two being increasingly used in the evaluation of the paediatric airway. The ultimate diagnostic test for evaluation of upper airway obstruction, however, is flexible endoscopy. ß 2004 Elsevier Ltd. All rights reserved.
History
positive in hereditary angioneurotic oedema. Birth and neonatal histories, as well as previous respiratory problems, should be explored in detail: the reason for and the duration of endotracheal intubation may be important clues to the evaluation of upper airway problems; trauma during birth (e.g. forceps delivery) may have caused vocal cord paralysis. Other important information includes the age at onset, the duration of stridor and an association with precipitating events such as crying or feeding, or an association with the infant’s position.1 In addition, the quality and nature of crying and the presence of other associated symptoms, such as fever, cough, aspiration or drooling may be helpful in establishing the diagnosis. Associated feeding difficulties may hint at the presence of a laryngeal cleft, or may be the symptoms of vocal cord paralysis or laryngeal cysts. Children with Chiari malformation and respiratory difficulties may have vocal cord paralysis. When stridor or hoarseness disappear with sleep, this could point to a functional nature of the problem (i.e. vocal cord dysfunction). This paradoxical vocal cord adduction was reported to be more common in young women with some health care background; in some cases there can be a combination of vocal cord dysfunction and bronchial asthma.2,3 In children with a history of choking or gagging, and subsequent cough, foreign body inhalation is likely; such patients must be referred for immediate airway endoscopy.
A careful history usually provides valuable guidance in the evaluation of the child with UAO. Family history may be
Physical examination
Correspondence to: Ernst Eber. Tel.: þ43 316 385 2620; Fax: þ43 316 385 4621; E-mail: [email protected]
The physical examination begins with observation. Particular notice should be taken of craniofacial morphology,
INTRODUCTION Upper airway obstruction (UAO) is an infrequent disorder in the newborn but is relatively common in infants and young children. Congenital forms can be differentiated from acquired, infectious from non-infectious and acute from chronic ones. Numerous causes can be distinguished in the newborn and infant; most of them are congenital abnormalities. In contrast, there are relatively few causes in children and croup (acute laryngotracheobronchitis) is the most frequent one. UAO may be life-threatening; thus, early and accurate diagnosis and treatment are essential. Evaluation of the child with UAO starts with a detailed history followed by a thorough physical examination, including an assessment of severity. In many cases, a correct diagnosis can be made or at least supected by history and physical examination. Depending on the age of the patient and the suspected aetiology, additional studies such as pulmonary function testing, imaging studies and especially the endoscopic evaluation of the airway, may be helpful in establishing the diagnosis. In case of respiratory distress, intervention may be necessary before aetiologic evaluation can take place.
CLINICAL ASSESSMENT
1526–0542/$ – see front matter
ß 2004 Elsevier Ltd. All rights reserved.
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skin colour, use of accessory muscles of respiration, nasal flaring, chest wall retractions and level of consciousness. The profile of the mandible should be inspected for the presence of retrognathia or micrognathia, both of which may lead to airway obstruction, especially during sleep. Swollen facial tissues and often urticaria suggest angioedema. These patients may also exhibit abdominal pain. If cough is present, its character can provide important clues to the aetiology. A ‘barking’ character of the cough (especially at night) suggests croup. A harsh (croupy) cough is common in children with tracheal lesions. Inspection enables assessment of work of breathing. Patients with UAO must generate increased negative intrathoracic pressures. To achieve this, they use the accessory muscles of respiration such as the sternocleidomastoid muscles, which will be prominent on physical examination. Other signs of increased work of breathing are nasal flaring as an attempt to reduce nasal resistance to airflow and retractions of the soft tissues of the chest wall as a consequence of increased negative pleural pressures during inspiration. Areas of retraction include the suprasternal notch, the subxiphoid region and the costal interspaces. In infants and toddlers, the sternum itself draws in during inspiration, a manifestation of the highly compliant rib cage in this age group. If the obstruction is long-standing, a permanent chest-wall deformity of the pectus excavatum type may result. In the older child, suprasternal and intercostal retractions predominate. With increasing negative pleural pressures, dynamic collapse of the soft extrathoracic airways results, further worsening UAO and feeding a vicious cycle. Stridor, a variably pitched respiratory sound, is often the most prominent symptom of UAO. It is caused by tissue vibration from airflow of increased turbulence and velocity passing through a narrowed segment of the large airways. Usually, stridor is indicative of substantial narrowing or obstruction of the larynx or extrathoracic trachea. In minor degrees of narrowing, breathing may be quiet at rest; with increased activity (e.g. crying) and consequently increased velocity of airflow, however, stridor may develop. Stridor is predominantly an inspiratory sound, although, in some infants with subglottic lesions (particularly if there is involvement of the upper trachea as well) a soft expiratory element may be noted. Biphasic stridor suggests severe, fixed airway obstruction at the level of the glottis or subglottis but lesions extending down to the midtracheal region may also result in inspiratory and expiratory stridor. In neonates, the most common causes of biphasic stridor are vocal cord paralysis and subglottic stenosis.1 Loud stridor usually is believed to represent a significant narrowing of the airway; however, a sudden decrease in volume sometimes can signify worsening obstruction and decreasing air movement. The character of the voice often provides important information. Hoarseness with or without stridor suggests an abnormality of the vocal cords (e.g. laryngeal web, vocal cord paralysis, enlodgement of a foreign body, oedema). Narrowing of the glottis itself results in hoarseness with a
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high-pitched inspiratory stridor. A muffled voice associated with a low-pitched stridor but no hoarseness may indicate a supraglottic process such as epiglottitis, whereas a weak voice accompanied by a high-pitched inspiratory stridor but no hoarseness can result from a subglottic obstruction. Another physical sign sometimes associated with UAO is pulsus paradoxus. This is the fluctuation in arterial systolic blood pressure with the respiratory cycle, the pressure falling during inspiration and rising with expiration. Pulsus paradoxus is quantified as the difference between the systolic pressures measured during inspiration and expiration. It can be detected by palpation when the difference is greater than 20 mmHg. Pulsus paradoxus was reported to be elevated in children with croup, and its magnitude to correlate with severity as measured by the Westley croup score.4 Most physicians and paediatricians, however, no longer measure pulsus paradoxus because of the difficulty in its measurement and interpretation. Acute UAO may present with pulmonary oedema. The pathogenesis of pulmonary oedema associated with UAO is multifactorial, with a markedly negative intrapleural pressure being the dominant pathophysiological mechanism (‘negative pressure pulmonary oedema’). The frequency of the event is impossible to ascertain from the literature, but paediatric cases requiring airway intervention for croup or epiglottitis account for over 50% of the documented cases. Most cases present within minutes of either the development of acute severe UAO or of relief of the obstruction.5 The nasal passages can often be visualised through the use of an otoscope and an ear speculum. Foul-smelling or bloody secretions may suggest a foreign body, whereas clear secretions may be related to an uncomplicated upper respiratory tract infection. The relative patency of the passages can be assessed by asking the child to sniff while manually occluding one naris; in the younger child simple listening may suffice. As a submucous cleft palate can easily be missed on inspection, the integrity of the palate should be assessed preferably be gentle palpation. A bifid uvula may be a clue to an occult submucous cleft palate. Intraoral examination should include attention to signs of infection, swelling or poor handling of secretions. The presence and size of the tonsils, as well as any other masses, especially unilateral enlargement as seen in retropharyngeal or tonsillar abscess, should be noted. The posterior part of the tongue should be palpated in all infants with stridor in order to identify or rule out a cyst arising from the tongue. Thyroglossal or mucus retention cysts can cause sudden asphyxiation. The neck should be palpated for adenopathy and masses; the latter may lead to deviation of the trachea. A child presenting with a rapidly progressive illness and characteristic signs and symptoms such as toxicity, fever, sore throat, muffled voice, dysphagia and drooling is likely to suffer from epiglottitis. Such children should be approached in a calm and reassuring manner, and physical
EVALUATION OF THE UPPER AIRWAY
examination should be deferred, as emotional upset may precipitate complete airway obstruction. Although laryngeal foreign bodies typically produce pain, laryngeal spasm, inspiratory stridor and hoarseness, foreign bodies lodged in the region of the cricopharyngeus muscle produce dysphagia and drooling rather than stridor. When foreign-body inhalation is suspected, immediate visualisation of the airway is required. Although the clinical features often suggest the type of airway abnormality present in a newborn, an endoscopic examination is usually necessary to guide management. Similarly infants with persistent stridor should be investigated endoscopically to establish a precise diagnosis so that appropriate treatment can be planned and an accurate prognosis can be given to the parents. If there are any unusual features, investigation is always essential.
Assessment of severity A previously healthy infant or child will readily tolerate UAO of moderate severity. With increasing obstruction, tidal volume is maintained virtually to the point of exhaustion, at which time hypoxaemia, hypercapnia and acidosis progress rapidly, and cardiorespiratory arrest will follow soon unless the obstruction is relieved.6 Arterial blood gas analysis,7 transcutaneous measurement of carbon dioxide pressure,8 changes in tracheal diameter as measured by fluoroscopy,9 thoraco-abdominal asynchrony assessed by non-calibrated inductance plethysmography10 and noninvasively measured pulsus paradoxus4 were suggested as objective measures of severity; however, none of these methods has been established in clinical practice. As noninvasive objective measures of the severity of UAO are still to be developed, it is standard practice to judge the severity of UAO clinically. Thus, accurate assessment of the severity and response to treatment of UAO relies on subjective parameters and often may be difficult. Stridor is a poor indicator of the severity of obstruction, because it may decrease with worsening obstruction. Severity of dyspnoea, increase in tachypnoea, poor air entry, tachycardia, cyanosis, evidence of fatigue and level of consciousness and responsivity of the child are generally used to predict the onset of respiratory failure and the need for an artificial airway. Measurable signs (e.g. pulse rate or respiratory rate) may be of much less clinical value than the child’s general appearance to an experienced observer.6 Scoring systems based on clinical signs have been developed and are often used as measures of severity.11,12
PHYSIOLOGIC STUDIES Blood gas determinations Hypoxia and hypercapnia (the latter occuring only late in the course of UAO) may develop as complications of UAO7,8 and the absence of cyanosis does not preclude
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the possibility of mild to moderate hypoxaemia. Respiratory rate was reported to be an indicator of lowered arterial oxygen tension7 in children with croup associated with pulmonary disease due to extension of the viral infection into the lower airways or, alternatively, with pulmonary oedema and resultant ventilation-perfusion abnormalities. In children with severe croup, monitoring of transcutaneous carbon dioxide pressure was reported to be a reliable tool for patient management, whereas croup scores were found to be misleading.8 With hypoxaemia and hypercapnia, the need for intervention is urgent.
Pulmonary function testing Respiratory inductive plethysmography Several investigators have attempted to assess objectively the severity of UAO and the response to treatment by respiratory inductive plethysmography in infants and small children. In this age group, UAO results in thoraco-abdominal asynchrony secondary to the easily distorted, highly compliant chest wall. In an earlier study10 the phase angle from the rib cage vs. abdominal signal curve was found to be significantly higher in children with upper airway obstruction compared with control children and treatment-induced changes in the phase angle were associated with changes in the degree of stridor in most children. Animal model work of the same group subsequently showed that monitoring of the relative changes in phase angles is useful to observe the severity of UAO only in early stages, and does not predict the development of hypercapnia secondary to inspiratory load.13 Recently, respiratory inductive plethysmography was reported to be insufficiently accurate for predicting the severity of UAO, and not useful as a predictor of UAO in the clinical or research setting.14
Flow-volume loop analysis Lung function analysis can be used only in patients with minor UAO, because the measurement itself may disturb the patient and lead to deterioration. In infants and young children with persistent stridor, tidal breathing flow-volume loop analysis may be used as a first diagnostic approach, that may add useful information to the initial physical examination. Recently, it has been shown to be a rapid, non-invasive and accurate method for establishing the site of airway obstruction in these patients.15 In addition, by comparing serial evaluations in the same patient, this technique may be used to evaluate pharmacological or surgical interventions. In patients who are able to co-operate, obtaining maximal inspiratory and expiratory flow-volume loops is a simple and effective method of non-invasively evaluating a patient for the presence of a UAO.16 Visual interpretation of the flow-volume loop allows variable and fixed lesions to be distinguished. The flow-volume loop in a patient with
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Figure 1 Maximal inspiratory and expiratory flow-volume loop of a 16-year-old boy with glottic stenosis.
variable extrathoracic airway obstruction is characterised by a plateau in the inspiratory limb due to increased obstruction during inspiration as a result of collapse of the extrathoracic structures. This form of flow-volume loop occurs with laryngomalacia, supraglottic tumour and viral croup. The flow-volume loop in a patient with fixed obstruction is characterised by plateaus in the inspiratory and expiratory limbs, as inspiratory and expiratory flows are reduced to the same extent. This ‘box-shaped’ loop may be seen in glottic, subglottic or tracheal stenosis (Fig. 1). Flowvolume loop analysis measures the functional rather than the anatomical degree of obstruction, and provides a simple non-invasive way of monitoring the response to treatment.17 In addition, flow-volume loops may be used to calculate the ratio of FEF50% to FIF50%. With extrathoracic airway obstruction, flow is reduced during inspiration and is maintained better during expiration, thus giving rise to a higher than normal FEF50%/FIF50% ratio (i.e. larger than or equal to 1).18,19
IMAGING Plain radiography Imaging studies aim at further defining a lesion and its extent or character, and are therefore complementary to flexible endoscopy. Usually, radiographic evaluation of the airway begins with plain films as a screening modality. Although plain films can provide a detailed view of the adenoid and tonsil size, nasopharyngeal vault, epiglottic shadow, retropharyngeal soft tissue profile and subglottic and tracheal air columns they can be inaccurate and must be considered in context with history, physical examination and clinical suspicion.20 For standard evaluation of the airway, magnification radiographs, using a high kilovolt technique and added filtration, are obtained. When a foreign body is
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suspected, a low kilovolt x-ray is obtained to maximise the contrast between the foreign body and tissue. Slightly opaque objects such as small bones can be missed with high kilovolt radiographs. A number of radiographs can be obtained for the same or less radiation as is delivered during short fluoroscopy. Once severe airway obstruction is present, radiography will cause undue delay in definitive treatment and may precipitate respiratory arrest. In this situation, an x-ray should not be taken, unless it appears absolutely necessary in exceptional circumstances. In straightforward viral croup, further investigations are rarely necessary. Occasionally, radiographs of the neck, especially a lateral view with the head in extension during inspiration, may be useful in differentiating croup from other causes of UAO, such as a foreign body or retropharyngeal abscess. The radiologic appearance of croup is characteristic, albeit not specific. Corresponding to symmetric subglottic oedema, antero-posterior neck radiographs demonstrate a pointed or spire-shaped configuration (‘steeple-sign’) rather than the normal dome-shaped appearance of the upper trachea under the vocal folds.21 In some cases of viral croup, however, asymmetric narrowing of the subglottic space can be seen, a finding suggestive of other entities such as haemangioma or acquired subglottic stenosis. Lateral neck radiographs show subglottic narrowing, usually extending a centimeter below the glottis and sometimes inspiratory distention.21 The radiographic appearance of acute epiglottitis (or, more appropriately, supraglottitis) is characteristic. Classic findings in the lateral neck radiograph include loss of distinctive anatomy with enlargement of the epiglottis, thickening of the aryepiglottic folds that join with the epiglottis to produce a mass-like appearance and distention of the hypopharynx.21 Isolated thickening of the epiglottis is not diagnostic of acute supraglottitis because an omegashaped epiglottis can have a similar appearance in the lateral neck radiograph. Swelling of the epiglottis also may be caused by oedema from allergic reaction, a foreign body, cyst or tumour. In bacterial tracheitis, antero-posterior and lateral projections may provide roentgenographic evidence of narrowing of the subglottic area.22,23 The epiglottis and aryepiglottic folds are normal, unless epiglottitis co-exists. The tracheal mucosa may appear to be irregular as a result of the formation of pseudomembranes. Lateral x-ray films often suggest the presence of radio-opaque foreign material in the tracheal lumen, which represents a detached tracheal pseudomembrane.23 There is some controversy about the benefits of radiographs in the evaluation of croup and epiglottitis. Radiographic changes heavily depend on the stage of the respiratory cycle during which they are taken. Inspiratory distention of the hypopharynx often is seen in children with UAO, but occasionally can be a normal finding.21 Radiographs are unreliable in reflecting the severity of airway obstruction, and may be inaccurate in the diagnosis of croup
EVALUATION OF THE UPPER AIRWAY
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and epiglottitis. Thus, caution and good clinical judgement should be used when interpreting these radiographs.24
Fluoroscopy Fluoroscopy can be used to clarify uncertain radiographic findings or to study functional aspects. Furthermore, fluoroscopic examination can be used to evaluate children suspected of foreign-body aspiration. The amount of radiation delivered, even in a short fluoroscopy, is considerable and thus argues for using this technique only in exceptional circumstances.
Computed tomography In the past, tomography was considered to be the procedure of choice for imaging airway lesions. Today, it has largely been replaced by computed tomography (CT). As infants and young children do not routinely co-operate and remain motionless for a longer period, they may require sedation for CT or magnetic resonance imaging (MRI). If possible, sedation should be avoided as it carries particular hazards in the child with a compromised airway. Compared with MRI, CT is more readily available, is not as affected by motion and gives better spatial resolution. Disadvantages of CT include the application of ionising radiation and the inability to image the trachea along its long axis. CT is the modality of choice for investigating the causes of nasal obstruction in the neonate and infant. It provides confirmation of the clinical diagnosis choanal atresia, and also clearly separates bony atresia patients from those with membranous choanal atresia.25 The best method of visualisation of a retropharyngeal mass is CT with intravenous contrast medium. Ultrafast CT with short data acquisition times is of particular value in evaluating the airways of infants and children. In a comparison with clinical and surgical data, ultrafast CT was shown to provide an accurate, minimally invasive method for dynamic imaging of the airways in nonsedated children.26 A study comparing ultrafast CT with endoscopy concluded that, for the greatest diagnostic accuracy with ultrafast CT in evaluation of the paediatric airway, both cine and high-resolution modes should be used.27 In patients with UAO, CT-based virtual endoscopy has been shown to be useful in assessing fixed airway lesions; however, it was not as sensitive as actual endoscopy in detecting dynamic airway obstruction.28 Virtual endoscopy allows further evaluation of high-grade stenosis that cannot be passed by actual endoscopy. In addition, it offers the possibility of identifying the structures around the airway, which is advantageous in cases with suspected airway compression.
Magnetic resonance imaging MRI is increasingly used in the evaluation of the paediatric airway, and is the preferred technique for imaging of the
Figure 2 Coronal T1-weighted magnetic resonance scan of a 3-month-old girl. Right-sided subglottic haemangioma (arrow).
trachea in infants and young children. Its advantages over CT include multiplanar imaging, good resolution without contrast injection, estimation of the length and degree of tracheal obstruction, evaluation of mediastinal involvement and lack of ionising radiation. As a disadvantage, MRI requires prolonged and greater sedation. MRI is particularly useful in the assessment of masses (Fig. 2) and evaluation of vascular compression of the airway.29 In addition, MRI is useful for analysing in detail the upper airway structure, size, and motion in children with obstructive sleep apnoea.30,31
Contrast studies Today, angiography has little use in airway evaluation because most vascular structures causing airway obstruction are better evaluated with MRI or CT. Similarly, tracheography has been replaced by alternative methods such as flexible endoscopy, MRI and CT. Contrast oesophagography may be used to evaluate the patency of the oesophageal inlet and to rule out aspiration through a tracheo-oesophageal fistula or a patent posterior laryngeal cleft. In infants with persistent stridor, especially with an expiratory component, a barium swallow examination may help in establishing the diagnosis of a vascular ring.
Ultrasound Ultrasound of the larynx may be used in the evaluation of functional disorders and space-occupying lesions in infants and children.32 A typical application of sonography is to differentiate cystic and solid masses.
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ENDOSCOPY Indirect evaluation of airway anatomy and function using radiographic or pulmonary function studies may provide important information in infants and children with UAO. In many patients, however, direct evaluation of the airway (i.e. visual examination) is required to determine specific causes and guide definitive interventions. Endoscopy, therefore, remains by far the most important diagnostic tool for the evaluation of UAO.
Rigid versus flexible endoscopy Rigid and flexible endoscopy are complementary methods, each with specific advantages in different situations. Rigid bronchoscopy is the method of choice for removal of a foreign body. In addition, it is ideal for documenting the pathology of the posterior glottis, subglottis and trachea, such as laryngeal cleft and H-type tracheo-oesophageal fistula. On the other hand, flexible bronchoscopes are considered the instruments of choice for most bronchoscopies and ultrathin endoscopes were repeatedly reported to be extremely useful in infants and young children with airway abnormalities.33–35 Advantages of flexible bronchoscopy include the avoidance of general anaesthesia, the low incidence of complications (e.g. subglottic oedema) and, as a result of less mechanical interference by the instrument, a reliable assessment of dynamic airway lesions, which is particularly relevant for patients with stridor (Fig. 3a and b). Thus, flexible bronchoscopes are adequate for the diagnosis of most causes of UAO; sometimes they also serve as a valuable aid to accomplish difficult intubations with tubes as small as 2.5 mm in the intensive care unit or the operating room.36 Provided adequate training and constant practice of the endoscopist, flexible bronchoscopy is a safe and valuable diagnostic tool for the investigation of children with UAO.35,37,38 Endoscopic findings frequently serve as the basis for early and accurate therapeutic intervention.
Figure 3 (a) Flexible airway endoscopy of a 4-month-old girl with laryngomalacia; laryngeal opening during expiration and (b) closure during inspiration.
Flexible endoscopy: technique In general, flexible endoscopes are passed through the nose. This transnasal approach allows the entire upper airway to be examined in detail, and leaves the head and neck in a neutral position so that the dynamics of the pharynx and larynx can be observed without any distortion. As the patients may be examined with only mild sedation, vocal cord movements can be fully evaluated. Recently, it was shown that, in infants and children undergoing flexible bronchoscopy, topical anaesthesia with lidocaine may exaggerate the findings commonly associated with laryngomalacia.39 Thus, it is important to examine the supraglottic parts of the larynx before applying topical anaesthesia. When a lesion causing sig-
nificant airway obstruction is detected, the endoscope should not be passed beyond the point of obstruction in order to avoid further narrowing due to oedema. With this exception, a strong case can be made for including endoscopy of the lower airways, even when the primary indication for the procedure involves the upper airway because upper airway lesions are frequently associated with lower airway lesions. Several studies have shown, that, in 14–26% of patients with persistent stridor, significant additional lower airway abnormalities, or two or more synchronous airway lesions may be detected.37,40,41 It is a generally accepted
EVALUATION OF THE UPPER AIRWAY
standard to videotape endoscopic investigations. Where dynamic changes occur very rapidly, a replay of the procedure (in slow motion) may help to understand the nature of the lesion. Furthermore, videotaping is a useful tool for communicating findings to colleagues and families.
Flexible endoscopy: indications Sometimes it is difficult to decide whether to perform endoscopy in an infant who develops stridor at the age of some weeks or months. In infants and children with viral croup, endoscopy is rarely indicated unless there is no response to treatment or stridor persists longer than 2 weeks. Direct examination of the airway is indicated in virtually all infants with persistent stridor, especially when stridor is progressive or associated with apnoeas, difficulty in feeding or growth retardation. Stridor is one of the most common indications for diagnostic airway endoscopy in infants and children,35,37,42–46 and endoscopy has a high diagnostic yield in patients with stridor.41,44,45,47,48 Children with stridor should be examined while they are stridulous, as the vibrating structures should then always be visible.49 In many cases, ‘negative’ findings are as important as ‘positive’ findings. The documentation of laryngomalacia and the exclusion of other causes of stridor in an infant usually alleviates parental anxiety and may prevent further diagnostic evaluation. Other indications for endoscopic evaluation may be abnormal cry or hoarseness (with or without stridor) persisting for longer than 2 weeks. Possible endoscopic findings include vocal cord paralysis and laryngeal papillomatosis. Unless mild sedation is used, the diagnosis of vocal cord paralysis, particularly of the unilateral form, may be difficult to establish. Children with atypical croup, characterised by prolonged symptoms, lack of response to treatment or an age less than 6 months should also be investigated by flexible endoscopy. The reason for investigating a child with recurrent croup (especially if there were episodes of severe or prolonged stridor) is to determine whether a pre-existing lesion (e.g. subglottic stenosis) favours the development of stridor with respiratory infections. When a patient with vocal cord dysfunction is symptomatic, the diagnosis can be confirmed by visualisation of a paradoxical inspiratory narrowing of the anterior portion of the vocal cords during inspiration. Flexible endoscopy has also proved to be a useful method for assessing symptomatic patients after extubation. Although some infants or children fail immediately and require reintubation, in others it may take hours or even days to develop UAO. Therefore, in some patients initial endoscopic findings may be normal as a result of temporary stenting by the endotracheal tube and the later development of oedema.
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PRACTICE POINTS Upper airway obstruction is common in infants and young children. In many cases, a correct diagnosis can be made by history and physical examination. Clinical scoring systems are unreliable in the assessment of severity. Maximal inspiratory and expiratory flow-volume loop analysis is a simple and effective method for evaluating a patient with upper airway obstruction non-invasively. Radiographs are unreliable in reflecting the severity of airway obstruction. For many patients with upper airway obstruction, flexible endoscopy is by far the most important diagnostic tool.
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15. Filippone M, Narne S, Pettenazzo A, Zacchello F, Baraldi E. Functional approach to infants and young children with noisy breathing: validation of pneumotachography by blinded comparison with bronchoscopy. Am J Respir Crit Care Med 2000; 162: 1795–1800. 16. Lunn WW, Sheller JR. Flow volume loops in the evaluation of upper airway obstruction. Otolaryngol Clin North Am 1995; 28: 721–729. 17. Couriel JM, Hibbert M, Olinsky A. Assessment of proximal airway obstruction in children by analysis of flow-volume loops. Br J Dis Chest 1984; 78: 36–45. 18. Miller RD, Hyatt RE. Evaluation of obstructing lesions of the trachea and larynx by flow-volume loops. Am Rev Respir Dis 1973; 108: 475–481. 19. Rotman HH, Liss HP, Weg JG. Diagnosis of upper airway obstruction by pulmonary function testing. Chest 1975; 68: 796–799. 20. Walner DL, Ouanounou S, Donnelly LF, Cotton RT. Utility of radiographs in the evaluation of pediatric upper airway obstruction. Ann Otol Rhinol Laryngol 1999; 108: 378–383. 21. Capitanio MA, Kirkpatrick JA Jr. Upper respiratory tract obstruction in infants and children. Radiol Clin North Am 1968; 6: 265–277. 22. Liston SL, Gehrz RC, Siegel LG, Tilelli J. Bacterial tracheitis. Am J Dis Child 1983; 137: 764–767. 23. Henry RL, Mellis CM, Benjamin B. Pseudomembranous croup. Arch Dis Child 1983; 58: 180–183. 24. Stankiewicz JA, Bowes AK. Croup and epiglottitis: a radiologic study. Laryngoscope 1985; 95: 1159–1160. 25. Slovis TL, Renfro B, Watts FB, Kuhns LR, Belenky W, Spoylar J. Choanal atresia: precise CT evaluation. Radiology 1985; 155: 345–348. 26. Brasch RC, Gould RG, Gooding CA, Ringertz HG, Lipton MJ. Upper airway obstruction in infants and children: evaluation with ultrafast CT. Radiology 1987; 165: 459–466. 27. Brody AS, Kuhn JP, Seidel FG, Brodsky LS. Airway evaluation in children with use of ultrafast CT: pitfalls and recommendations. Radiology 1991; 178: 181–184. 28. Burke AJ, Vining DJ, McGuirt WF Jr, Postma G, Browne JD. Evaluation of airway obstruction using virtual endoscopy. Laryngoscope 2000; 110: 23–29. 29. Vogl T, Wilimzig C, Bilaniuk LT et al. MR imaging in pediatric airway obstruction. J Comput Assist Tomogr 1990; 14: 182–186. 30. Arens R, McDonough JM, Corbin AM et al. Upper airway size analysis by magnetic resonance imaging of children with obstructive sleep apnea syndrome. Am J Respir Crit Care Med 2003; 167: 65–70. 31. Donnelly LF, Surdulescu V, Chini BA, Casper KA, Poe SA, Amin RS. Upper airway motion depicted at cine MR imaging performed during sleep: comparison between young patients with and those without obstructive sleep apnea. Radiology 2003; 227: 239–245.
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32. Garel C, Contencin P, Polonovski JM, Hassan M, Narcy P. Laryngeal ultrasonography in infants and children: a new way of investigating. Normal and pathological findings. Int J Pediatr Otorhinolaryngol 1992; 23: 107–115. 33. Fan LL, Sparks LM, Fix EJ. Flexible fiberoptic endoscopy for airway problems in a pediatric intensive care unit. Chest 1988; 93: 556–560. 34. De Blic J, Delacourt C, Scheinmann P. Ultrathin flexible bronchoscopy in neonatal intensive care units. Arch Dis Child 1991; 66: 1383–1385. 35. Eber E, Zach M. Flexible fiberoptic bronchoscopy in pediatrics: an analysis of 420 examinations. Wien Klin Wochenschr 1995; 107: 246–251. 36. Finer NN, Muzyka D. Flexible endoscopic intubation of the neonate. Pediatr Pulmonol 1992; 12: 48–51. 37. Wood RE. Spelunking in the pediatric airways: explorations with the flexible fiberoptic bronchoscope. Pediatr Clin North Am 1984; 31: 785–799. 38. De Blic J, Marchac V, Scheinmann P. Complications of flexible bronchoscopy in children: prospective study of 1,328 procedures. Eur Respir J 2002; 20: 1271–1276. 39. Nielson DW, Ku PL, Egger M. Topical lidocaine exaggerates laryngomalacia during flexible bronchoscopy. Am J Respir Crit Care Med 2000; 161: 147–151. 40. Gonzalez C, Reilly JS, Bluestone CD. Synchronous airway lesions in infancy. Ann Otol Rhinol Laryngol 1987; 96: 77–80. 41. Eber E, Zach M. Flexible fiberoptic endoscopy in children with upper airway obstruction. Monatsschr Kinderheilkd 1996; 144: 43–47. 42. Holinger LD. Etiology of stridor in the neonate, infant and child. Ann Otol Rhinol Laryngol 1980; 89: 397–400. 43. Nussbaum E. Usefulness of miniature flexible fiberoptic bronchoscopy in children. Chest 1994; 106: 1438–1442. 44. Godfrey S, Avital A, Maayan C, Rotschild M, Springer C. Yield from flexible bronchoscopy in children. Pediatr Pulmonol 1997; 23: 261–269. 45. Barbato A, Magarotto M, Crivellaro M et al. Use of the paediatric bronchoscope, flexible and rigid, in 51 European centres. Eur Respir J 1997; 10: 1761–1766. 46. Nicolai T. Pediatric bronchoscopy. Pediatr Pulmonol 2001; 31: 150–164. 47. Wood RE. The diagnostic effectiveness of the flexible bronchoscope in children. Pediatr Pulmonol 1985; 1: 188–192. 48. Lis G, Szczerbinski T, Cichocka-Jarosz E. Congenital stridor. Pediatr Pulmonol 1995; 20: 220–224. 49. Wood RE. Pitfalls in the use of the flexible bronchoscope in pediatric patients. Chest 1990; 97: 199–203.
MINI-SYMPOSIUM: UPPER AIRWAY OBSTRUCTION
Evaluation of the upper airway Ernst Eber Respiratory and Allergic Disease Division, Paediatric Department, University of Graz, Austria KEYWORDS children; endoscopy; imaging; infants; pulmonary function testing; upper airway obstruction
Summary The evaluation of infants and children with upper airway obstruction always involves a history and physical examination, which in many cases allow a diagnosis to be made. Assessment of severity and response to treatment relies on subjective parameters. Flow-volume loop analysis is a rapid, simple and effective method of evaluating patients with upper airway obstruction non-invasively. Imaging studies are complementary to endoscopy, and include plain radiography as well as computed tomography and magnetic resonance imaging, with the latter two being increasingly used in the evaluation of the paediatric airway. The ultimate diagnostic test for evaluation of upper airway obstruction, however, is flexible endoscopy. ß 2004 Elsevier Ltd. All rights reserved.
History
positive in hereditary angioneurotic oedema. Birth and neonatal histories, as well as previous respiratory problems, should be explored in detail: the reason for and the duration of endotracheal intubation may be important clues to the evaluation of upper airway problems; trauma during birth (e.g. forceps delivery) may have caused vocal cord paralysis. Other important information includes the age at onset, the duration of stridor and an association with precipitating events such as crying or feeding, or an association with the infant’s position.1 In addition, the quality and nature of crying and the presence of other associated symptoms, such as fever, cough, aspiration or drooling may be helpful in establishing the diagnosis. Associated feeding difficulties may hint at the presence of a laryngeal cleft, or may be the symptoms of vocal cord paralysis or laryngeal cysts. Children with Chiari malformation and respiratory difficulties may have vocal cord paralysis. When stridor or hoarseness disappear with sleep, this could point to a functional nature of the problem (i.e. vocal cord dysfunction). This paradoxical vocal cord adduction was reported to be more common in young women with some health care background; in some cases there can be a combination of vocal cord dysfunction and bronchial asthma.2,3 In children with a history of choking or gagging, and subsequent cough, foreign body inhalation is likely; such patients must be referred for immediate airway endoscopy.
A careful history usually provides valuable guidance in the evaluation of the child with UAO. Family history may be
Physical examination
Correspondence to: Ernst Eber. Tel.: þ43 316 385 2620; Fax: þ43 316 385 4621; E-mail: [email protected]
The physical examination begins with observation. Particular notice should be taken of craniofacial morphology,
INTRODUCTION Upper airway obstruction (UAO) is an infrequent disorder in the newborn but is relatively common in infants and young children. Congenital forms can be differentiated from acquired, infectious from non-infectious and acute from chronic ones. Numerous causes can be distinguished in the newborn and infant; most of them are congenital abnormalities. In contrast, there are relatively few causes in children and croup (acute laryngotracheobronchitis) is the most frequent one. UAO may be life-threatening; thus, early and accurate diagnosis and treatment are essential. Evaluation of the child with UAO starts with a detailed history followed by a thorough physical examination, including an assessment of severity. In many cases, a correct diagnosis can be made or at least supected by history and physical examination. Depending on the age of the patient and the suspected aetiology, additional studies such as pulmonary function testing, imaging studies and especially the endoscopic evaluation of the airway, may be helpful in establishing the diagnosis. In case of respiratory distress, intervention may be necessary before aetiologic evaluation can take place.
CLINICAL ASSESSMENT
1526–0542/$ – see front matter
ß 2004 Elsevier Ltd. All rights reserved.
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skin colour, use of accessory muscles of respiration, nasal flaring, chest wall retractions and level of consciousness. The profile of the mandible should be inspected for the presence of retrognathia or micrognathia, both of which may lead to airway obstruction, especially during sleep. Swollen facial tissues and often urticaria suggest angioedema. These patients may also exhibit abdominal pain. If cough is present, its character can provide important clues to the aetiology. A ‘barking’ character of the cough (especially at night) suggests croup. A harsh (croupy) cough is common in children with tracheal lesions. Inspection enables assessment of work of breathing. Patients with UAO must generate increased negative intrathoracic pressures. To achieve this, they use the accessory muscles of respiration such as the sternocleidomastoid muscles, which will be prominent on physical examination. Other signs of increased work of breathing are nasal flaring as an attempt to reduce nasal resistance to airflow and retractions of the soft tissues of the chest wall as a consequence of increased negative pleural pressures during inspiration. Areas of retraction include the suprasternal notch, the subxiphoid region and the costal interspaces. In infants and toddlers, the sternum itself draws in during inspiration, a manifestation of the highly compliant rib cage in this age group. If the obstruction is long-standing, a permanent chest-wall deformity of the pectus excavatum type may result. In the older child, suprasternal and intercostal retractions predominate. With increasing negative pleural pressures, dynamic collapse of the soft extrathoracic airways results, further worsening UAO and feeding a vicious cycle. Stridor, a variably pitched respiratory sound, is often the most prominent symptom of UAO. It is caused by tissue vibration from airflow of increased turbulence and velocity passing through a narrowed segment of the large airways. Usually, stridor is indicative of substantial narrowing or obstruction of the larynx or extrathoracic trachea. In minor degrees of narrowing, breathing may be quiet at rest; with increased activity (e.g. crying) and consequently increased velocity of airflow, however, stridor may develop. Stridor is predominantly an inspiratory sound, although, in some infants with subglottic lesions (particularly if there is involvement of the upper trachea as well) a soft expiratory element may be noted. Biphasic stridor suggests severe, fixed airway obstruction at the level of the glottis or subglottis but lesions extending down to the midtracheal region may also result in inspiratory and expiratory stridor. In neonates, the most common causes of biphasic stridor are vocal cord paralysis and subglottic stenosis.1 Loud stridor usually is believed to represent a significant narrowing of the airway; however, a sudden decrease in volume sometimes can signify worsening obstruction and decreasing air movement. The character of the voice often provides important information. Hoarseness with or without stridor suggests an abnormality of the vocal cords (e.g. laryngeal web, vocal cord paralysis, enlodgement of a foreign body, oedema). Narrowing of the glottis itself results in hoarseness with a
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high-pitched inspiratory stridor. A muffled voice associated with a low-pitched stridor but no hoarseness may indicate a supraglottic process such as epiglottitis, whereas a weak voice accompanied by a high-pitched inspiratory stridor but no hoarseness can result from a subglottic obstruction. Another physical sign sometimes associated with UAO is pulsus paradoxus. This is the fluctuation in arterial systolic blood pressure with the respiratory cycle, the pressure falling during inspiration and rising with expiration. Pulsus paradoxus is quantified as the difference between the systolic pressures measured during inspiration and expiration. It can be detected by palpation when the difference is greater than 20 mmHg. Pulsus paradoxus was reported to be elevated in children with croup, and its magnitude to correlate with severity as measured by the Westley croup score.4 Most physicians and paediatricians, however, no longer measure pulsus paradoxus because of the difficulty in its measurement and interpretation. Acute UAO may present with pulmonary oedema. The pathogenesis of pulmonary oedema associated with UAO is multifactorial, with a markedly negative intrapleural pressure being the dominant pathophysiological mechanism (‘negative pressure pulmonary oedema’). The frequency of the event is impossible to ascertain from the literature, but paediatric cases requiring airway intervention for croup or epiglottitis account for over 50% of the documented cases. Most cases present within minutes of either the development of acute severe UAO or of relief of the obstruction.5 The nasal passages can often be visualised through the use of an otoscope and an ear speculum. Foul-smelling or bloody secretions may suggest a foreign body, whereas clear secretions may be related to an uncomplicated upper respiratory tract infection. The relative patency of the passages can be assessed by asking the child to sniff while manually occluding one naris; in the younger child simple listening may suffice. As a submucous cleft palate can easily be missed on inspection, the integrity of the palate should be assessed preferably be gentle palpation. A bifid uvula may be a clue to an occult submucous cleft palate. Intraoral examination should include attention to signs of infection, swelling or poor handling of secretions. The presence and size of the tonsils, as well as any other masses, especially unilateral enlargement as seen in retropharyngeal or tonsillar abscess, should be noted. The posterior part of the tongue should be palpated in all infants with stridor in order to identify or rule out a cyst arising from the tongue. Thyroglossal or mucus retention cysts can cause sudden asphyxiation. The neck should be palpated for adenopathy and masses; the latter may lead to deviation of the trachea. A child presenting with a rapidly progressive illness and characteristic signs and symptoms such as toxicity, fever, sore throat, muffled voice, dysphagia and drooling is likely to suffer from epiglottitis. Such children should be approached in a calm and reassuring manner, and physical
EVALUATION OF THE UPPER AIRWAY
examination should be deferred, as emotional upset may precipitate complete airway obstruction. Although laryngeal foreign bodies typically produce pain, laryngeal spasm, inspiratory stridor and hoarseness, foreign bodies lodged in the region of the cricopharyngeus muscle produce dysphagia and drooling rather than stridor. When foreign-body inhalation is suspected, immediate visualisation of the airway is required. Although the clinical features often suggest the type of airway abnormality present in a newborn, an endoscopic examination is usually necessary to guide management. Similarly infants with persistent stridor should be investigated endoscopically to establish a precise diagnosis so that appropriate treatment can be planned and an accurate prognosis can be given to the parents. If there are any unusual features, investigation is always essential.
Assessment of severity A previously healthy infant or child will readily tolerate UAO of moderate severity. With increasing obstruction, tidal volume is maintained virtually to the point of exhaustion, at which time hypoxaemia, hypercapnia and acidosis progress rapidly, and cardiorespiratory arrest will follow soon unless the obstruction is relieved.6 Arterial blood gas analysis,7 transcutaneous measurement of carbon dioxide pressure,8 changes in tracheal diameter as measured by fluoroscopy,9 thoraco-abdominal asynchrony assessed by non-calibrated inductance plethysmography10 and noninvasively measured pulsus paradoxus4 were suggested as objective measures of severity; however, none of these methods has been established in clinical practice. As noninvasive objective measures of the severity of UAO are still to be developed, it is standard practice to judge the severity of UAO clinically. Thus, accurate assessment of the severity and response to treatment of UAO relies on subjective parameters and often may be difficult. Stridor is a poor indicator of the severity of obstruction, because it may decrease with worsening obstruction. Severity of dyspnoea, increase in tachypnoea, poor air entry, tachycardia, cyanosis, evidence of fatigue and level of consciousness and responsivity of the child are generally used to predict the onset of respiratory failure and the need for an artificial airway. Measurable signs (e.g. pulse rate or respiratory rate) may be of much less clinical value than the child’s general appearance to an experienced observer.6 Scoring systems based on clinical signs have been developed and are often used as measures of severity.11,12
PHYSIOLOGIC STUDIES Blood gas determinations Hypoxia and hypercapnia (the latter occuring only late in the course of UAO) may develop as complications of UAO7,8 and the absence of cyanosis does not preclude
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the possibility of mild to moderate hypoxaemia. Respiratory rate was reported to be an indicator of lowered arterial oxygen tension7 in children with croup associated with pulmonary disease due to extension of the viral infection into the lower airways or, alternatively, with pulmonary oedema and resultant ventilation-perfusion abnormalities. In children with severe croup, monitoring of transcutaneous carbon dioxide pressure was reported to be a reliable tool for patient management, whereas croup scores were found to be misleading.8 With hypoxaemia and hypercapnia, the need for intervention is urgent.
Pulmonary function testing Respiratory inductive plethysmography Several investigators have attempted to assess objectively the severity of UAO and the response to treatment by respiratory inductive plethysmography in infants and small children. In this age group, UAO results in thoraco-abdominal asynchrony secondary to the easily distorted, highly compliant chest wall. In an earlier study10 the phase angle from the rib cage vs. abdominal signal curve was found to be significantly higher in children with upper airway obstruction compared with control children and treatment-induced changes in the phase angle were associated with changes in the degree of stridor in most children. Animal model work of the same group subsequently showed that monitoring of the relative changes in phase angles is useful to observe the severity of UAO only in early stages, and does not predict the development of hypercapnia secondary to inspiratory load.13 Recently, respiratory inductive plethysmography was reported to be insufficiently accurate for predicting the severity of UAO, and not useful as a predictor of UAO in the clinical or research setting.14
Flow-volume loop analysis Lung function analysis can be used only in patients with minor UAO, because the measurement itself may disturb the patient and lead to deterioration. In infants and young children with persistent stridor, tidal breathing flow-volume loop analysis may be used as a first diagnostic approach, that may add useful information to the initial physical examination. Recently, it has been shown to be a rapid, non-invasive and accurate method for establishing the site of airway obstruction in these patients.15 In addition, by comparing serial evaluations in the same patient, this technique may be used to evaluate pharmacological or surgical interventions. In patients who are able to co-operate, obtaining maximal inspiratory and expiratory flow-volume loops is a simple and effective method of non-invasively evaluating a patient for the presence of a UAO.16 Visual interpretation of the flow-volume loop allows variable and fixed lesions to be distinguished. The flow-volume loop in a patient with
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Figure 1 Maximal inspiratory and expiratory flow-volume loop of a 16-year-old boy with glottic stenosis.
variable extrathoracic airway obstruction is characterised by a plateau in the inspiratory limb due to increased obstruction during inspiration as a result of collapse of the extrathoracic structures. This form of flow-volume loop occurs with laryngomalacia, supraglottic tumour and viral croup. The flow-volume loop in a patient with fixed obstruction is characterised by plateaus in the inspiratory and expiratory limbs, as inspiratory and expiratory flows are reduced to the same extent. This ‘box-shaped’ loop may be seen in glottic, subglottic or tracheal stenosis (Fig. 1). Flowvolume loop analysis measures the functional rather than the anatomical degree of obstruction, and provides a simple non-invasive way of monitoring the response to treatment.17 In addition, flow-volume loops may be used to calculate the ratio of FEF50% to FIF50%. With extrathoracic airway obstruction, flow is reduced during inspiration and is maintained better during expiration, thus giving rise to a higher than normal FEF50%/FIF50% ratio (i.e. larger than or equal to 1).18,19
IMAGING Plain radiography Imaging studies aim at further defining a lesion and its extent or character, and are therefore complementary to flexible endoscopy. Usually, radiographic evaluation of the airway begins with plain films as a screening modality. Although plain films can provide a detailed view of the adenoid and tonsil size, nasopharyngeal vault, epiglottic shadow, retropharyngeal soft tissue profile and subglottic and tracheal air columns they can be inaccurate and must be considered in context with history, physical examination and clinical suspicion.20 For standard evaluation of the airway, magnification radiographs, using a high kilovolt technique and added filtration, are obtained. When a foreign body is
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suspected, a low kilovolt x-ray is obtained to maximise the contrast between the foreign body and tissue. Slightly opaque objects such as small bones can be missed with high kilovolt radiographs. A number of radiographs can be obtained for the same or less radiation as is delivered during short fluoroscopy. Once severe airway obstruction is present, radiography will cause undue delay in definitive treatment and may precipitate respiratory arrest. In this situation, an x-ray should not be taken, unless it appears absolutely necessary in exceptional circumstances. In straightforward viral croup, further investigations are rarely necessary. Occasionally, radiographs of the neck, especially a lateral view with the head in extension during inspiration, may be useful in differentiating croup from other causes of UAO, such as a foreign body or retropharyngeal abscess. The radiologic appearance of croup is characteristic, albeit not specific. Corresponding to symmetric subglottic oedema, antero-posterior neck radiographs demonstrate a pointed or spire-shaped configuration (‘steeple-sign’) rather than the normal dome-shaped appearance of the upper trachea under the vocal folds.21 In some cases of viral croup, however, asymmetric narrowing of the subglottic space can be seen, a finding suggestive of other entities such as haemangioma or acquired subglottic stenosis. Lateral neck radiographs show subglottic narrowing, usually extending a centimeter below the glottis and sometimes inspiratory distention.21 The radiographic appearance of acute epiglottitis (or, more appropriately, supraglottitis) is characteristic. Classic findings in the lateral neck radiograph include loss of distinctive anatomy with enlargement of the epiglottis, thickening of the aryepiglottic folds that join with the epiglottis to produce a mass-like appearance and distention of the hypopharynx.21 Isolated thickening of the epiglottis is not diagnostic of acute supraglottitis because an omegashaped epiglottis can have a similar appearance in the lateral neck radiograph. Swelling of the epiglottis also may be caused by oedema from allergic reaction, a foreign body, cyst or tumour. In bacterial tracheitis, antero-posterior and lateral projections may provide roentgenographic evidence of narrowing of the subglottic area.22,23 The epiglottis and aryepiglottic folds are normal, unless epiglottitis co-exists. The tracheal mucosa may appear to be irregular as a result of the formation of pseudomembranes. Lateral x-ray films often suggest the presence of radio-opaque foreign material in the tracheal lumen, which represents a detached tracheal pseudomembrane.23 There is some controversy about the benefits of radiographs in the evaluation of croup and epiglottitis. Radiographic changes heavily depend on the stage of the respiratory cycle during which they are taken. Inspiratory distention of the hypopharynx often is seen in children with UAO, but occasionally can be a normal finding.21 Radiographs are unreliable in reflecting the severity of airway obstruction, and may be inaccurate in the diagnosis of croup
EVALUATION OF THE UPPER AIRWAY
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and epiglottitis. Thus, caution and good clinical judgement should be used when interpreting these radiographs.24
Fluoroscopy Fluoroscopy can be used to clarify uncertain radiographic findings or to study functional aspects. Furthermore, fluoroscopic examination can be used to evaluate children suspected of foreign-body aspiration. The amount of radiation delivered, even in a short fluoroscopy, is considerable and thus argues for using this technique only in exceptional circumstances.
Computed tomography In the past, tomography was considered to be the procedure of choice for imaging airway lesions. Today, it has largely been replaced by computed tomography (CT). As infants and young children do not routinely co-operate and remain motionless for a longer period, they may require sedation for CT or magnetic resonance imaging (MRI). If possible, sedation should be avoided as it carries particular hazards in the child with a compromised airway. Compared with MRI, CT is more readily available, is not as affected by motion and gives better spatial resolution. Disadvantages of CT include the application of ionising radiation and the inability to image the trachea along its long axis. CT is the modality of choice for investigating the causes of nasal obstruction in the neonate and infant. It provides confirmation of the clinical diagnosis choanal atresia, and also clearly separates bony atresia patients from those with membranous choanal atresia.25 The best method of visualisation of a retropharyngeal mass is CT with intravenous contrast medium. Ultrafast CT with short data acquisition times is of particular value in evaluating the airways of infants and children. In a comparison with clinical and surgical data, ultrafast CT was shown to provide an accurate, minimally invasive method for dynamic imaging of the airways in nonsedated children.26 A study comparing ultrafast CT with endoscopy concluded that, for the greatest diagnostic accuracy with ultrafast CT in evaluation of the paediatric airway, both cine and high-resolution modes should be used.27 In patients with UAO, CT-based virtual endoscopy has been shown to be useful in assessing fixed airway lesions; however, it was not as sensitive as actual endoscopy in detecting dynamic airway obstruction.28 Virtual endoscopy allows further evaluation of high-grade stenosis that cannot be passed by actual endoscopy. In addition, it offers the possibility of identifying the structures around the airway, which is advantageous in cases with suspected airway compression.
Magnetic resonance imaging MRI is increasingly used in the evaluation of the paediatric airway, and is the preferred technique for imaging of the
Figure 2 Coronal T1-weighted magnetic resonance scan of a 3-month-old girl. Right-sided subglottic haemangioma (arrow).
trachea in infants and young children. Its advantages over CT include multiplanar imaging, good resolution without contrast injection, estimation of the length and degree of tracheal obstruction, evaluation of mediastinal involvement and lack of ionising radiation. As a disadvantage, MRI requires prolonged and greater sedation. MRI is particularly useful in the assessment of masses (Fig. 2) and evaluation of vascular compression of the airway.29 In addition, MRI is useful for analysing in detail the upper airway structure, size, and motion in children with obstructive sleep apnoea.30,31
Contrast studies Today, angiography has little use in airway evaluation because most vascular structures causing airway obstruction are better evaluated with MRI or CT. Similarly, tracheography has been replaced by alternative methods such as flexible endoscopy, MRI and CT. Contrast oesophagography may be used to evaluate the patency of the oesophageal inlet and to rule out aspiration through a tracheo-oesophageal fistula or a patent posterior laryngeal cleft. In infants with persistent stridor, especially with an expiratory component, a barium swallow examination may help in establishing the diagnosis of a vascular ring.
Ultrasound Ultrasound of the larynx may be used in the evaluation of functional disorders and space-occupying lesions in infants and children.32 A typical application of sonography is to differentiate cystic and solid masses.
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ENDOSCOPY Indirect evaluation of airway anatomy and function using radiographic or pulmonary function studies may provide important information in infants and children with UAO. In many patients, however, direct evaluation of the airway (i.e. visual examination) is required to determine specific causes and guide definitive interventions. Endoscopy, therefore, remains by far the most important diagnostic tool for the evaluation of UAO.
Rigid versus flexible endoscopy Rigid and flexible endoscopy are complementary methods, each with specific advantages in different situations. Rigid bronchoscopy is the method of choice for removal of a foreign body. In addition, it is ideal for documenting the pathology of the posterior glottis, subglottis and trachea, such as laryngeal cleft and H-type tracheo-oesophageal fistula. On the other hand, flexible bronchoscopes are considered the instruments of choice for most bronchoscopies and ultrathin endoscopes were repeatedly reported to be extremely useful in infants and young children with airway abnormalities.33–35 Advantages of flexible bronchoscopy include the avoidance of general anaesthesia, the low incidence of complications (e.g. subglottic oedema) and, as a result of less mechanical interference by the instrument, a reliable assessment of dynamic airway lesions, which is particularly relevant for patients with stridor (Fig. 3a and b). Thus, flexible bronchoscopes are adequate for the diagnosis of most causes of UAO; sometimes they also serve as a valuable aid to accomplish difficult intubations with tubes as small as 2.5 mm in the intensive care unit or the operating room.36 Provided adequate training and constant practice of the endoscopist, flexible bronchoscopy is a safe and valuable diagnostic tool for the investigation of children with UAO.35,37,38 Endoscopic findings frequently serve as the basis for early and accurate therapeutic intervention.
Figure 3 (a) Flexible airway endoscopy of a 4-month-old girl with laryngomalacia; laryngeal opening during expiration and (b) closure during inspiration.
Flexible endoscopy: technique In general, flexible endoscopes are passed through the nose. This transnasal approach allows the entire upper airway to be examined in detail, and leaves the head and neck in a neutral position so that the dynamics of the pharynx and larynx can be observed without any distortion. As the patients may be examined with only mild sedation, vocal cord movements can be fully evaluated. Recently, it was shown that, in infants and children undergoing flexible bronchoscopy, topical anaesthesia with lidocaine may exaggerate the findings commonly associated with laryngomalacia.39 Thus, it is important to examine the supraglottic parts of the larynx before applying topical anaesthesia. When a lesion causing sig-
nificant airway obstruction is detected, the endoscope should not be passed beyond the point of obstruction in order to avoid further narrowing due to oedema. With this exception, a strong case can be made for including endoscopy of the lower airways, even when the primary indication for the procedure involves the upper airway because upper airway lesions are frequently associated with lower airway lesions. Several studies have shown, that, in 14–26% of patients with persistent stridor, significant additional lower airway abnormalities, or two or more synchronous airway lesions may be detected.37,40,41 It is a generally accepted
EVALUATION OF THE UPPER AIRWAY
standard to videotape endoscopic investigations. Where dynamic changes occur very rapidly, a replay of the procedure (in slow motion) may help to understand the nature of the lesion. Furthermore, videotaping is a useful tool for communicating findings to colleagues and families.
Flexible endoscopy: indications Sometimes it is difficult to decide whether to perform endoscopy in an infant who develops stridor at the age of some weeks or months. In infants and children with viral croup, endoscopy is rarely indicated unless there is no response to treatment or stridor persists longer than 2 weeks. Direct examination of the airway is indicated in virtually all infants with persistent stridor, especially when stridor is progressive or associated with apnoeas, difficulty in feeding or growth retardation. Stridor is one of the most common indications for diagnostic airway endoscopy in infants and children,35,37,42–46 and endoscopy has a high diagnostic yield in patients with stridor.41,44,45,47,48 Children with stridor should be examined while they are stridulous, as the vibrating structures should then always be visible.49 In many cases, ‘negative’ findings are as important as ‘positive’ findings. The documentation of laryngomalacia and the exclusion of other causes of stridor in an infant usually alleviates parental anxiety and may prevent further diagnostic evaluation. Other indications for endoscopic evaluation may be abnormal cry or hoarseness (with or without stridor) persisting for longer than 2 weeks. Possible endoscopic findings include vocal cord paralysis and laryngeal papillomatosis. Unless mild sedation is used, the diagnosis of vocal cord paralysis, particularly of the unilateral form, may be difficult to establish. Children with atypical croup, characterised by prolonged symptoms, lack of response to treatment or an age less than 6 months should also be investigated by flexible endoscopy. The reason for investigating a child with recurrent croup (especially if there were episodes of severe or prolonged stridor) is to determine whether a pre-existing lesion (e.g. subglottic stenosis) favours the development of stridor with respiratory infections. When a patient with vocal cord dysfunction is symptomatic, the diagnosis can be confirmed by visualisation of a paradoxical inspiratory narrowing of the anterior portion of the vocal cords during inspiration. Flexible endoscopy has also proved to be a useful method for assessing symptomatic patients after extubation. Although some infants or children fail immediately and require reintubation, in others it may take hours or even days to develop UAO. Therefore, in some patients initial endoscopic findings may be normal as a result of temporary stenting by the endotracheal tube and the later development of oedema.
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PRACTICE POINTS Upper airway obstruction is common in infants and young children. In many cases, a correct diagnosis can be made by history and physical examination. Clinical scoring systems are unreliable in the assessment of severity. Maximal inspiratory and expiratory flow-volume loop analysis is a simple and effective method for evaluating a patient with upper airway obstruction non-invasively. Radiographs are unreliable in reflecting the severity of airway obstruction. For many patients with upper airway obstruction, flexible endoscopy is by far the most important diagnostic tool.
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