Respiratory Distress

Pulmonary Physical Examination

The physical examination begins with measurement of vital signs, with attention paid to respiratory rate, pulse oximetry, heart rate, and blood pressure. Tachypnea is often the most prominent manifestation of respiratory distress. A respiratory rate of more than 50 breaths/min in infants 2–12 months of age, 40 breaths/min in children 1–5 years, and 30 breaths/min in children older than 5 years is abnormal. The physical examination should be performed in a warm, well-lit room, preferably with the child in the parent’s lap and the child’s chest exposed. It is essential to observe the child’s general appearance, sense of well-being, degree of dyspnea or cyanosis, and respiratory pattern, including nasal flaring, retractions, and accessory muscle use. Central cyanosis (lips, tongue, sublingual tissue as well as hands and feet) is related to both the degree of oxygen desaturation and the hemoglobin level ( Table 4.4 ). Cyanosis is detected when the average amount of deoxygenated hemoglobin is 5 g/dL. Any posture assumed in an effort to minimize the airway difficulties should be determined. The degree and location of retractions should be noted. Retractions may be intercostal, subcostal, or suprasternal, and often signify worsening respiratory distress, particularly in the older child. Infants have a particularly compliant chest wall and are therefore more predisposed to intercostal and sternal retractions; in older children, these features may be less prominent. Nasal flaring and accessory muscle use signify significant respiratory distress; and, as fatigue sets in, head bobbing and/or grunting can be noted, which requires prompt management as this may be a sign of impending respiratory failure. Altered mental status (either agitation or somnolence) may be indicative of severe respiratory distress, hypoxemia, hypercapnia, and impending respiratory failure. Palpation of the chest wall and cervical region may enable the examiner to detect the presence of subcutaneous emphysema indicative of pulmonary air leak. On percussion of the chest and back, a hyperresonant note during percussion of the chest wall indicates hyperinflation, whereas dullness to percussion suggests atelectasis, pulmonary consolidation, or pleural effusion.

Auscultation of the chest should focus on identifying the degree of air exchange and the presence, timing, and symmetry of adventitious breath sounds. Air entry should be evaluated over all discrete anatomic locations bilaterally. Homologous segments of each lung should be examined sequentially to compare similar areas. The presence of adventitious sounds should be determined next. The most encountered sounds are wheezing, stridor, crackles, and rhonchi ( Table 4.5 ).

Crackles (previously called “rales”) are intermittent, nonmusical low- or higher-pitched, largely inspiratory noises that are produced by the opening (reinflation) of groups of alveoli closed during the previous expiration.

Wheezing is a continuous, high-pitched musical noise, similar to a hiss or whistle.

Rhonchi are continuous sounds that are lower pitched and more rumbling or sonorous, heard more during expiration, and primarily heard over the trachea and bronchi; however, if loud enough they can be heard throughout all lung fields.

Stridor is a high-pitched musical noise generated by turbulent flow of air through the large upper airways.

Other adventitious breath sounds that are described include pleural rub, which has a grating quality heard best during inspiration, and stertor, a low-pitched, nonmusical noise generated by the vibration of the pharyngeal tissues (nasopharynx, oropharynx, soft palate) due to significant upper respiratory obstruction and subsequent turbulent airflow downstream in the upper airway heard only during inspiration. Determination of the timing (inspiration, expiration, or biphasic) and distribution of the adventitious sounds offers clues as to the site of airway and lung involvement. Wheezing that is continuous and heard equally over both lung fields is associated with diffuse airway narrowing and limitation of airflow, whereas unilateral or very localized wheezing or decreased breath sounds suggest segmental airway obstruction, such as that found with retained foreign body aspiration, mucus plugging, or atelectasis. Additionally, inspiratory stridor is characteristic of partial airway obstruction at or above the vocal cords, whereas biphasic or expiratory stridor is characteristic of airway obstruction in the subglottic space or trachea ( Fig. 4.1 ).

Other Parts of the Physical Examination

Other elements of the physical examination may have direct bearing on the respiratory system. Pulsus paradoxus , the difference between the systolic blood pressure obtained during inspiration and during exhalation, is exaggerated by airway obstruction and pulmonary hyperinflation. As pulmonary overinflation gets worse, pulsus paradoxus values increase and correlate well with the degree of airway obstruction. It is difficult to measure pulsus paradoxus in young children with rapid heart rates. A method that allows a reasonable approximation of the pulsus paradoxus can be obtained by using a sphygmomanometer and noting the difference between the pressure at which the first sporadic faint pulse sounds and the pressure at which all sounds are heard. Values >10 mm Hg are abnormal, and values >20 mm Hg are consistent with severe airway obstruction. Although digital clubbing is very rarely seen as a normal and familial variant, its presence in a child with respiratory distress suggests an acute illness superimposed on an underlying chronic respiratory condition. The most common pulmonary causes of digital clubbing in pediatric patients are cystic fibrosis, bronchiectasis, and other destructive pulmonary diseases. Digital clubbing is rarely seen in children with asthma. Other physical findings to observe include mouth breathing and morphologic features suggestive of craniofacial anomalies, such as maxillary hypoplasia, nasal septal deflection, micrognathia, retrognathia, absent nasal airflow (choanal obstructions), platybasia, or macroglossia.

Radiography

A plain x-ray of the chest, taken in the posterior-anterior and lateral projections, should be obtained in any patient with respiratory distress in which an etiology has not been determined from the history and physical examination. Important information regarding the presence of parenchymal infiltrates, pleural effusions, airway obstruction, cardiac size, pulmonary vascular markings, extrapulmonary air leaks, and the presence of radiopaque foreign bodies may be obtained from this test. Radiopaque foreign bodies are generally seen easily on a radiograph. If there is a possibility of a radiolucent foreign body, inspiratory and expiratory chest radiographic studies must be performed. Demonstration of unilateral hyperinflation or a mediastinal shift during expiration suggests localized bronchial obstruction, such as a retained foreign body. Lateral decubitus positioning of the patient during the radiographic procedure can reveal a pleural effusion in the lower dependent lung. Ultrasonography of the chest is also useful in detecting pleural fluid and loculations within pleural effusions.

In patients with stridor, anteroposterior and lateral soft tissue radiographic studies of the neck and chest are frequently needed. These should be obtained during inspiration, because the soft tissues of the pharynx may bulge with expiration, causing a false-positive finding of a soft tissue mass that may mimic a retropharyngeal infection.

Computed Tomography

CT of the upper airway and chest can help detect the relationship of the vasculature to the airways (trachea and large central airways); pulmonary parenchymal lesions (infiltrates, abscesses, cysts) or lesions (abscesses, inflammation) in the airway; and central airway caliber. Rapid, fine-cut CT is a technique of high resolution and short duration, which increases its acceptability for pediatric patients. It is the method of choice for noninvasive detection and evaluation of bronchiectasis and interstitial lung disease. In some patients with a normal chest x-ray, the CT will be abnormal. Helical CT is a valuable method of detecting pulmonary embolism. A PET scan may be used in combination with a CT scan to evaluate for malignancy or other etiologies.

Magnetic Resonance Imaging

MRI of the pulmonary system may also be useful in elucidating the relationship of the great vessels to the airways and may be superior to CT for this purpose. MRI is less useful for imaging the lung parenchyma. The need for long imaging times often means sedation for young children, and this limits the utility of MRI of the chest for some pediatric patients. Sedatives must be used very carefully, particularly in patients with respiratory distress, and only in monitored situations with the availability of experienced personnel and equipment to provide possible resuscitation.

Fluoroscopy

Fluoroscopic examination of the chest may be useful in determining the cause of respiratory distress. Real-time visualization of the diaphragm can determine whether paralysis or paresis of this major muscle of respiration is contributing to respiratory distress. Asymmetric chest wall motion or unilateral hyperinflation during the respiratory cycle suggests bronchial obstruction, such as that seen with a retained foreign body in the airways. An upper gastrointestinal series is useful to assess for abnormalities of swallowing causing aspiration, presence of tracheoesophageal fistula, or presence of a vascular ring.

Endoscopy

Endoscopy can provide direct visualization of the cause of the airway obstruction and lung lesions; its use involves manipulation of the airway, which should not be undertaken unless the personnel and equipment are present to manage possible worsening airway compromise. Flexible, direct laryngoscopy is widely used to visualize the upper airway without the need for sedation. Rigid bronchoscopy provides visualization of both the upper and lower airways; cardiopulmonary monitoring and intravenous access for sedative administration are required. In cases of significant upper airway obstruction necessitating intervention, or if there is any likelihood of a foreign body, direct laryngoscopy and rigid bronchoscopy in the operating room are the safest procedures that can secure the airway, provide a diagnosis, and accomplish treatment.

Wheezing

Wheezing is best characterized as a continuous musical sound most often heard on expiration, but it may occur in both phases of respiration. The most common causes of acute wheezing in children are bronchiolitis and asthma. However, it is critical to rule out other causes of wheezing that necessitate different therapy ( Table 4.6 ). Anatomic abnormalities of the airway, such as vascular ring, tracheobronchomalacia, primary ciliary dyskinesia, and foreign body aspiration, may cause airway obstruction and wheezing, especially in infants and young children. Viral infections, notably those of respiratory syncytial virus (RSV), human metapneumovirus, adenovirus, parainfluenza, and influenza, are also common causes of wheezing (bronchiolitis) in infants and young children. Infection with Mycoplasma species may produce airway hyperactivity in older children. Other entities to consider are cystic fibrosis, interstitial lung disease, or vocal cord dysfunction. In comparison with asthma, one key distinguishing feature of these diagnoses is that the wheezing does not respond to treatment with bronchodilators.

Asthma

Asthma is defined as airway obstruction that is reversible either spontaneously or with the use of medication. Chronic airway inflammation and bronchial hyperresponsiveness are the likely causes of the airway obstruction. The airways of patients with even mild asthma demonstrate inflammation, manifested as mucosal edema, hypersecretion of mucus, smooth muscle constriction, and inflammatory cell infiltrate. Even when asthma symptoms are not present, airway inflammation may be demonstrated. Furthermore, bronchial hyperresponsiveness, the tendency of airway smooth muscle to constrict in response to a variety of environmental stimuli, is present in virtually all children with asthma and may be exacerbated by airway inflammation. Airway remodeling, the deposition of collagen in the subepithelial basement membrane area, occurs in some but not all asthmatic patients. Fixed airway obstruction is a long-term complication that may occur as a result of airway remodeling.

The diagnosis of asthma is made by a combination of history, physical examination, and spirometry testing. For the child with acute wheezing and respiratory distress, a therapeutic trial of an inhaled β-agonist is the best “diagnostic test” for reversible airway obstruction. Once the acute symptoms have improved, other diagnostic studies can be undertaken. Spirometry, particularly measurement of the forced expiratory volume in 1 second (FEV ₁ ) and mid-maximal forced expiratory flow rates (FEF _25–75% ), provides a good indication of airflow obstruction in the larger and smaller airways, respectively. If airway obstruction is detected in the resting state, a bronchodilator (typically albuterol) is administered, and spirometry is repeated. An improvement of ≥12% and ≥200 mL in FEV ₁ above baseline is considered significant and indicative of reversible airway obstruction ( Fig. 4.2 ). If the baseline spirometry is normal, an inhalation challenge test, with either increasing doses of methacholine or hyperventilation of cold, dry air, can provoke a statistically (but usually not clinically) significant decrease in FEV ₁ ; a fall in FEV ₁ of 10% or greater is considered diagnostic of airway hyperresponsiveness and asthma. In children too young to perform spirometry (typically under the age of 5 years), the repeated nature of wheezing episodes and the improvement in symptoms after treatment with antiinflammatory agents and bronchodilators, peripheral blood eosinophilia (>4%), a family history of atopy, and/or a personal history of atopy (eczema, food allergy, or allergic rhinitis) are strongly suggestive of the diagnosis of asthma. Other studies include measurement of total serum immunoglobulin E (IgE) levels. This immunoglobulin is often elevated in individuals with asthma and/or allergy, as well as in those predisposed to asthma.

Patients with acute asthma typically present with shortness of breath, wheezing, cough, and increased work of breathing. Persistent cough may be the most prominent or even sole feature of acute asthma (see Chapter 3 ). Many asthma episodes are misdiagnosed as bronchitis (which is rare in children). Chest wall retractions and the use of accessory muscles indicate significant airway obstruction. Acute asthma exacerbations that are unresponsive to aggressive bronchodilator administration are termed status asthmaticus . The severity of asthma exacerbation may be assessed with the parameters presented in Table 4.7 . Common triggers of acute asthma episodes include upper respiratory tract infections, exposure to cold air, exercise, allergens, pollutants, strong odors, and tobacco smoke.

A brief history should be obtained for every child with acute asthma to determine the duration of symptoms, the character of previous episodes (severity, need for hospitalization, and need for intensive care, including mechanical ventilation), antecedent illness, symptoms, exposures, and both chronic and acute use of medications, including dose and time of last administration. History should also focus on identifying risk factors for severe asthma ( Table 4.8 ) and classification of asthma type, which are based on age ( Figs. 4.3, 4.4, and 4.5 ). It is also important to assess the degree of asthma control. The physical examination should focus on respiratory rate, air exchange, degree and localization of wheezing, other adventitious lung sounds, mental status, presence of cyanosis, and degree of fatigue. A chest radiograph should be obtained for all patients with a first episode of wheezing to evaluate for other causes of wheezing if clinically indicated. Patients with recurrent asthma should have a chest radiograph if there is evidence for a foreign body or pneumonia, or concern for a pneumothorax. Chest radiograph findings in asthma are nonspecific, but they usually show symmetric hyperinflation and increased peribronchial thickening. Spirometry has limited efficacy in the emergency management of status asthmaticus. Although peak expiratory flow rates are often measured, this test is a measure of large airway function only, is effort dependent, and may be unreliable in an anxious, untrained patient. The major value of peak flow measurements in acute asthma is to provide an objective trend indicative of improvement (or lack thereof) in airway caliber if frequent and scheduled treatments are needed.

A CBC is not of use unless other complicating conditions (i.e., bacterial infection, anemia, hemoglobinopathy) are suspected. Serum electrolyte measurements are of little value unless dehydration is suspected. Hypokalemia can be associated with the frequent administration of β-agonists.

Treatment of acute asthma should be instituted in any child with wheezing, dyspnea, cough, and no other immediately discernible cause of the symptoms. Patients with moderate to severe airway obstruction can have significant hypoxemia as a result of ventilation-perfusion mismatch. Consequently, supplemental humidified oxygen should be administered to any child who has significant wheezing, accessory muscle use, or an oxygen saturation of <93%. The mainstay of treatment for an asthma exacerbation is the administration of an inhaled β-adrenergic agonist and systemic corticosteroids. Inhalation of β-agonist by nebulizer or metered-dose inhaler is the route of choice because the onset of action is rapid, sustained, and relatively free of significant side effects even in the most severely affected patients. Anticholinergic agents (ipratropium bromide), when combined with a β-agonist as inhaled treatment, can provide additional bronchodilation. The effect is most marked in children who present to the emergency department with significant airway obstruction. With few exceptions, any patient who presents with wheezing responsive to bronchodilator therapy or any patient requiring hospital admission should receive corticosteroids. In severe respiratory distress, intravenous magnesium or theophylline (or the intravenous formulation aminophylline) may be of benefit. A small percentage of children with acute asthma progress to severe status asthmaticus and respiratory failure. A number of clinical signs and symptoms define respiratory failure in such severely affected patients: a Pa o ₂ <60 mm in room air or cyanosis in 40% F io ₂ , a Pa co ₂ of 40 mm or higher or rising and accompanied by respiratory distress, deterioration in clinical status in spite of aggressive treatment, a change in mental status, and fatigue. Patients meeting any of these criteria should be admitted to an intensive care unit.

Identification and treatment of chronic asthma require careful assessment of the severity of the disease, according to frequency and intensity of symptoms, and subsequent grading into mild, moderate, and severe categories (see Figs. 4.3, 4.4, and 4.5 ). All patients except those with mild intermittent disease are best managed with chronic administration of an inhaled antiinflammatory agent (corticosteroids) and the intermittent use of an inhaled β-agonist for treatment of acute wheezing episodes. Leukotriene receptor antagonists may be considered as an alternative preventive therapy for mild asthma. Oral corticosteroids are administered for short intervals to control more severe exacerbations. Avoidance of environmental triggers (allergens, tobacco smoke) is also paramount to successful management.

Bronchiolitis

Bronchiolitis is a common, acute viral infection of the distal lower respiratory tract, and is characterized as lower airway obstruction secondary to airway edema, mucus, and cellular debris. Impaired gas exchange can occur as a result of airway obstruction and ventilation-perfusion inequalities. RSV is the most important respiratory pathogen in infants and young children. In addition, it has been identified as the etiologic agent in 5–40% of pneumonias in young children. Other viruses, such as adenovirus, influenza, human metapneumovirus, parainfluenza, and coronavirus, can also cause bronchiolitis. The most severe disease occurs in infants younger than 6 months. By 5 years of age, 95% of all children have serologic evidence of RSV infection. Reinfections are common in older children and adults, because immunity to RSV is short lived and incomplete. In older children and adolescents, infections with RSV are often limited to the upper respiratory tract. In temperate climates, RSV epidemics occur yearly, beginning in midwinter and persisting through early spring.

In infected infants, upper respiratory tract symptoms usually precede the lower respiratory tract involvement by 3–7 days. Low-grade fever, rhinitis, and pharyngitis are common signs in the initial phase of the disease. This then progresses to cough, increased work of breathing, and wheezing (see Chapter 3 ). Apnea may also occur, particularly in infants younger than 3 months of age. Chest wall retractions and dyspnea are frequently observed, and adventitious sounds (wheezing, crackles) are appreciated on auscultation of the chest. Most children with bronchiolitis demonstrate clinical improvement after 5–7 days, but the duration of illness can be as long as 21 days. Bacterial superinfection of the lower respiratory tract is rare . Approximately 30% of infants with bronchiolitis caused by RSV have recurrent episodes of wheezing caused by bronchial hyperactivity and are diagnosed with asthma. This is in part due to persistent inflammation of the distal respiratory tract produced by the viral infection.

The clinical determination of the severity of the lower respiratory tract involvement in infants infected with bronchiolitis can be difficult. Physical findings often associated with respiratory distress, such as tachypnea, intercostal retractions, and wheezing, are not necessarily correlated with the level of hypoxemia. Carbon dioxide retention secondary to alveolar hypoventilation is not a common finding in otherwise previously normal children, but hypercapnia and acute respiratory acidosis can be serious problems in infants with chronic pulmonary disease or congenital heart disease. Chest radiograph findings include a diffuse interstitial pneumonitis and bilateral lung overinflation; alveolar infiltrates or consolidation are present in approximately 20% of children. Infants with congenital heart disease, pulmonary hypertension, prematurity, and young age (younger than 12 weeks) have an increased rate of severe disease and mortality; the course of illness is usually prolonged, and intensive care and mechanical ventilation are frequently needed.

The diagnosis of bronchiolitis is usually made on clinical grounds. Bronchiolitis is most common in children under 2 years of age and should be suspected in the wheezing child who has current or antecedent upper respiratory tract infection symptoms in the late fall or winter months. The definitive diagnosis of RSV or other viral infection is based on the presence of the viral genome in respiratory secretions. This testing is often not needed if the clinical findings are consistent with bronchiolitis. Polymerase chain reaction (PCR) testing is specific and accurate, and has a short turnaround time in identifying the virus from nasopharyngeal swabs.

Suctioning and supplemental oxygen remain the cornerstone of treatment for bronchiolitis if needed. Unlike asthma, the wheezing accompanying bronchiolitis is often less responsive to bronchodilators. Nonetheless, patients with significant hypoxia and hypercapnia may receive a trial treatment with aerosol bronchodilators to determine if this may improve symptoms, which may be continued if infants do show improvement. Infants with bronchiolitis do not respond to treatment with antiinflammatory agents, such as corticosteroids, so these are not recommended. Severely ill patients may require mechanical ventilation; heated, humidified, high-flow nasal cannula oxygen decreases intubation rates and is used in children with severe respiratory distress. Other modalities, such as hypertonic or normal saline aerosols, positive expiratory pressure (PEP) therapy, and chest physiotherapy have shown mixed results but may be of benefit for patients who are hospitalized.

Monthly administration (intramuscularly) of a humanized monoclonal antibody (palivizumab) against RSV can reduce morbidity from bronchiolitis but does not completely prevent infection. Infants at high risk (infants who are premature, those with bronchopulmonary dysplasia or other forms of chronic obstructive pulmonary disease, those with complex congenital heart disease) who are younger than 2 years are most likely to benefit.

Mycoplasma pneumoniae Infections

One of the basic tenets regarding respiratory infections in children is that “bacteria do not make you wheeze.” Mycoplasma pneumoniae is an exception to that rule and should be considered in an older child who presents with new-onset wheezing. In addition, infections with M. pneumoniae can precipitate exacerbations in patients with asthma. Productive or dry coughs secondary to tracheobronchitis are the most common symptoms of M. pneumoniae infections. Pulmonary symptoms span from mild viral symptoms to more severe presentations of pneumonia. Other clinical manifestations of M. pneumoniae infections include fever/chills, rhinorrhea, and otitis media (see Chapter 5 ). Extrapulmonary manifestations not only are due to the infection itself but also can be due to immune or vascular complications. Examples of M. pneumoniae extrapulmonary findings include hemolytic anemia, rash, mucositis, cardiac disease, polyarthritis, transverse myelitis, rhabdomyolysis, and central nervous system disease. The incidence of M. pneumoniae infection peaks between the ages of 5 and 19 years; the organism usually does not produce disease in children younger than age 2. Infections with M. pneumoniae tend to be seasonal, occurring most frequently during autumn and early winter.

The findings of M. pneumoniae on chest radiographs are variable. In about 5% of patients, the chest radiograph appears normal. A diffuse, bilateral, reticular infiltrate is the classic appearance in about half of patients. However, lobar, alveolar, and interstitial infiltrates have also been described ( Fig. 4.6 ). Enlargement of hilar or peritracheal lymph nodes may also be evident. Pleural effusions (usually small) are found in 14% of patients with M. pneumoniae . Atypical pneumonia (diffuse infiltrates with nonlobar pattern; fever, malaise, myalgias) is often caused by M. pneumoniae but may also be caused by Chlamydia pneumoniae , Legionella species, and other related pathogens. PCR may help to confirm a diagnosis. Many M. pneumoniae infections are self-limiting within 7–10 days. When antibiotics are used, treatment is with azithromycin. Doxycycline or fluoroquinolones may also be used in older children, although there is increasing emergence of M. pneumoniae resistance to macrolides in some areas of the world.