be the predominant presenting clinical feature and wheezing may be absent despite careful lung auscultation FIGURE 84.2 Approach to wheezing in children year or older URI, upper respiratory infection Physical Examination Wheezing must be distinguished from other causes of “noisy breathing” in children, including the stridor of upper airway obstruction (see Chapter 75 Stridor ), the stertor of nasal congestion, and audible rhonchi Because of the dynamic flexibility of airway structures, these clinical features of airway obstruction vary in accordance with the respiratory phase Accordingly, upper airway collapse and stridor are typically worse on inspiration, whereas lower airway narrowing and wheezing are accentuated on expiration Moreover, sounds originating in the upper airway passages (e.g., stridor, stertor) are transmitted with uniform quality and intensity across both lung fields In contrast, wheezes tend to be polyphonic in pitch and distributed somewhat unevenly in intensity and location due to inevitable variation in airway narrowing that occurs Importantly, wheezes consistently limited to a single lung field suggest a localized obstructive process, such as a foreign body, pneumonia, or an extrinsic mass lesion TABLE 84.3 MAJOR CAUSES OF WHEEZING WITH ASSOCIATED CLINICAL FEATURES Causes Bronchiolitis Associated clinical features Age 6 mo aspiration Choking episode associated with onset of symptoms Abrupt onset or prolonged symptoms despite appropriate therapy Unilateral wheezing or decreased breath sounds Intellectual disability History of tracheal surgery/tracheostomy Swallowing disorder, GE reflux Anaphylaxis Sudden onset Accompanying urticaria, angioedema, stridor, or hypotension New exposure or Hymenoptera envenomation Congestive heart History of failure to thrive failure/cardiac Heart murmur, hepatomegaly, poor perfusion disease Cardiomegaly Cystic fibrosis History of failure to thrive Recurrent respiratory tract infections Steatorrhea Adapted from Martinati LC, Boner AL Clinical diagnosis of wheezing in early childhood Allergy 1995;50:701–710 The intensity of wheezes and their pitch and duration are a function of the degree of airway narrowing and the velocity of airflow at the site(s) of obstruction In patients with minimal airway obstruction, wheezing may be difficult to detect When such instances are suspected, forced exhalation may reveal low-pitched wheezes limited to the end of expiration Subtle wheezes can be accentuated further by combining forced exhalation with simultaneous manual compression applied by the examiner in the anteroposterior dimension of the chest (the so-called “squeezing the wheeze”) As airway narrowing and minute ventilation increase, wheezes become louder and higher pitched However, when airway obstruction becomes more severe, airflow and wheezes will diminish proportionately A “quiet chest” in the face of significant respiratory distress may indicate impending respiratory failure Conversely, in patients with reversible bronchospasm, air exchange and wheezes are often noted to increase in response to bronchodilator therapy Auscultation of the neck may be used to determine the source of wheezing Wheezing heard only in the chest, and not the neck, is more likely to be associated with intrathoracic airway obstruction, whereas wheezing heard over the neck, but not in the chest, is more likely associated with upper airway causes of wheezing, such as psychogenic wheezing The clinical evaluation of a patient with obstructive lower airway disease will invariably reveal a prominent cough To the experienced clinician or parent, this cough will usually be perceived as having a characteristic whistling or “wheezy” quality that is distinct from the “seallike” barky cough of croup Physical examination of the wheezing child may also reveal inspiratory and expiratory crackles, which are far more often attributable to subsegmental atelectasis than to an associated pneumonia and parenchymal consolidation DIAGNOSTIC TESTS Most diagnoses can be made based on the clinical history and physical examination alone, but a limited number of diagnostic modalities may support the emergency department (ED) evaluation of the wheezing child The primary measurement that should accompany any patient with respiratory complaints is respiratory rate from pulse oximetry, which measures oxygenation Noninvasive end-tidal carbon dioxide measurements may also be used to assess ventilation When bronchiolitis or asthma is the clear diagnosis and the course is uncomplicated, a chest radiograph is not routinely indicated The available data ... history and physical examination alone, but a limited number of diagnostic modalities may support the emergency department (ED) evaluation of the wheezing child The primary measurement that should accompany