Chapter 15. Wheezing

Wheezing is a high-pitched whistling sound heard during expiration. It occurs when air flows through narrowed or partially obstructed airways, mostly the bronchioles. It can also be heard because of narrowing of larger airways.

Wheezing is common in infants and children. An estimated 10–15% of all infants younger than 1 year have an episode of wheezing. Up to 25% of children younger than 5 years present at least once to medical attention for evaluation of wheezing.1 Recurrent wheezing over the age of 1 year usually indicates a diagnosis of asthma.

The differential diagnosis for wheeze is broad.2 An initial episode of wheezing typically suggests viral respiratory tract infection. Since wheezing is often associated with viral respiratory infections in infants, it is difficult to distinguish an initial episode of asthma triggered by a viral respiratory tract infection from acute viral bronchiolitis. The causes of recurrent or persistent wheezing are more diverse. Common causes of recurrent wheezing include serial viral respiratory infections, poorly controlled asthma, and gastroesopheal reflux with pulmonary aspiration. Less commonly, recurrent wheezing is caused by congenital abnormalities of the lung, diaphragm, or branches of the aorta or pulmonary vessels. Vascular rings, aberrant right subclavian artery, innominate arterial compression, aberrant left pulmonary artery (pulmonary sling), and absence of the pulmonary valve may all present with abnormal respiratory sounds and distress in infants.3,4 Cystic fibrosis or immunologic defects may also manifest first with wheezing. In addition, wheezing may not be the reason why a caregiver brings a child to medical attention. Thus, children with wheeze can present in a variety of ways. These variable paths also provide clues to the etiology. Table 15–1 provides the most common presentations and associated signs and symptoms. Figure 15–1 provides anatomic locations of causes of wheezing.

A complete history and physicial examination will facilitate the accurate diagnosis of a child evaluated for wheezing. Features of the history that warrant clarification include the periodicity of the wheezing (initial, recurrent, or persistent), family history of pertinent medical conditions, relevant epidemiologic exposures, and presence of associated signs and symptoms.

For infants, a history of prematurity, mechanical ventilation (tracheal stenosis), or noisy breathing independent of symptoms of respiratory infection may suggest either bronchopulmonary dysplasia or a congenital structural airway abnormality. Investigate all perinatal screening to assess for HIV status of mother and child and pulmonary or cardiac anatomic anomaly that may have been seen on ultrasound. Delayed passage of meconium may be a clue for cystic fibrosis. Reflux, arching, or choking above the ordinary could be a sign that gastroesophageal reflux disease (GERD) or aspiration are a cause of wheezing. A history of sweating and/or difficulty with feeds suggests congenital heart disease and cardiac failure. Family history of asthma, cystic fibrosis, α1-antrypsin deficiency, immunodeficiency, or immotile cilia/Kartagener syndrome would be of interest. Relevant social history includes exposure to smoke or other exhaust, pets or animals, daycare, or travel. If tuberculosis is being considered, evaluate risk factors for exposure, including foreign travel, contact with visitors from other countries, or contact with prisoners or homeless shelters. Unusual causes of wheezing, such as histoplasmosis or other endemic fungi are more likely to occur after travel to the mid-Atlantic.

In younger children, wheezing may be hard to differentiate from stridor (harsh, high-pitched sound heard more on inspiration) or stertor (rattling and congested noise heard more on inspiration), or may accompany them. Auscultation in front of the nose and along the throat can help localize the source of the noisy breathing. Upper airway noises are also symmetrically distributed on ausculation of the chest, but wheezing can be localized or diffuse. Lack of wheezing may indicate insufficient respiratory effort by the patient or such severe narrowing of distal airways that air is not flowing to create an audible noise. Asking older children to breathe deeply or blow out, or assisting infants by compressing the chest on expiration, can make wheezing more apparent.

Physical examination should pay close attention to vital signs, with particular note of temperature, heart rate, respiratory rate, and pulse oximetry reading. Presence of fever should focus attention on infectious causes (such as pneumonia), though infants with bronchiolitis are often afebrile. Tachycardia may be a sign of signficant distress or dehydration. Preductal and postductal saturations or oxygen challenges may provide evidence toward heart disease. The presence of upper respiratory infection (URI) symptoms, including rhinorrhea, congestion, and sneezing may point toward a viral cause and bronchiolitis in an infant, but could also be a sign of an underlying anatomic or physiologic problem. In particular, patients with very severe illnesses that are associated with signs of URI should be evaluated in more depth.

Evidence of failure to thrive on examination should raise questions about prematurity and caloric intake, HIV status, and cystic fibrosis. Abnormal heart sounds, murmur on examination, or unequal pulses would raise the question of congenital heart disease.

Examination of a wheezing child can be done before and after bronchodilator therapy. Lack of any response to this treatment (or through history) may raise suspicion for a cause outside of the small airways. This would include congenital heart disease, aortic arch abnormalities, aberrant pulmonary veins, extrinsic compression of the trachea or bronchi, tracheobronchial anomalies, lung cysts, mediastinal masses, and thymus hyperplasia.

Chest Radiography

The need for laboratory or radiological studies depends on the presentation and level of concern. Chest radiography is often not needed in the evaluation of wheezing, especially in an infant with signs of a URI. In bronchiolitis or asthma, CXR may show hyperinflation, peribronchial thickening, and atelectasis. Plain film of the chest in anterior-posterior and lateral views may identify a right-sided or double aortic arch. The study can also delineate vascular anomaly, cardiac enlargement, or pulmonary hypertension. Plain film can also help elucidate the presence of a foreign body, but lateral decubitus films may be required (persistence of hyperinflation when lobe is down). CXR can also reveal infiltrates or masses, including mediastinal masses (Figure 15–2). Chest radiography is generally recommended in febrile patients or patients with focal findings (i.e., wheeze or rales) on pulmonary auscultation.5 Patients with recurrent wheezing, if they have not had a chest radiograph done, should have one to rule out an anatomic etiology for wheezing.

Other Studies

Blood-based laboratory studies are usually not needed for straightforward wheezing. A complete blood count may be indicated when evaluating for infection or anemia. Patients in severe respiratory distress, status asthmaticus, or with significant desaturations should have an arterial blood gas to evaluation for hypoxia, hypercarbia, and acidosis.

Rapid virologic testing for respiratory infections, such as influenza, RSV, and human metapneumovirus, are making their way into widespread clinical practice. The results rarely change management but can be helpful in cohorting hospitalized patients.

Other studies to consider in the wheezing patient, particularly those with chronic wheeze, would be sweat chloride test for cystic fibrosis, tuberculin skin test, allergy testing, and spirometry. Evaluation for airway and esophageal pathology (such as tracheoesophageal fistula) may be indicated in some cases. Difficult-to-control wheezing can be the result of gastroesophageal reflux disease with aspiration and studies to evaluate for those conditions may be needed.

Pulse oximetry is often used in the assessment of wheezing children, particularly those with evidence of bronchiolitis, pneumonia, and those in respiratory distress. Pulse oximetry can detect hypoxemia that is not evident on physical examination.6

Age, severity, associated symptoms, recurrence or persistence, and knowledge of past medical history will help guide evaluation of the wheezing child. Table 15–2 provides an algorithm of features of presentation and Table 15–1 provides laboratory or radiological studies associated with various diagnoses.

Depending on the severity of respiratory distress, the acuity or chronicity, age of the patient, likelihood of anatomic and mechanical etiology, associated findings, and location of presentation, consultation or referral may or may not be needed.

Infants and young children without significant tachypnea, desaturation, or respiratory distress can be managed on an outpatient basis with caregiver understanding of reasons to return to medical attention and assurance of good follow-up.

Any patient in extremis, status asthmaticus, or respiratory distress should be referred to an emergency department through emergency medical services. In bronchiolitis, high-risk patients include premature infants (≤34 weeks gestational age), infants younger than 3 months, those with respiratory rate greater than 70 breaths per minute or an underlying immunodeficiency; they are at increased risk for severe disease and should be referred to a hospital for evaluation and monitoring.

Patients with chronic wheezing not associated with infections, and who are difficult to control with standard outpatient measures, may be referred to allergy or pulmonary specialists for further evaluation and management. Patients at risk for GERD or aspiration may need additional evaluation and referral to a gastroenterologist.