History

Beyond the narrative provided by the parent and in older patients, the history should include questions about respiratory symptoms (dyspnea, cough, pain, wheezing, snoring, apnea, cyanosis), chronicity, timing during day or night, and associations with activities such as exercise or food intake. The respiratory system interacts with a number of other systems, and questions related to cardiac, gastrointestinal, central nervous, hematologic, and immune systems may be relevant. Questions related to gastrointestinal reflux, congenital abnormalities (airway anomalies, ciliary dyskinesia), or immune status may be important in a patient with repeated pneumonia. The family history is essential and should include inquiries about siblings and other close relatives with similar symptoms or any chronic disease with respiratory components.

Physical Examination

Respiratory dysfunction usually produces detectable alterations in the pattern of breathing. Values for normal respiratory rates are presented in Table 62-1 and depend on many factors, most importantly, age. Repeated respiratory rate measurements are necessary because respiratory rates, especially in the young, are exquisitely sensitive to extraneous stimuli. Sleeping respiratory rates are more reproducible in infants than those obtained during feeding or activity. These rates vary among infants but average 40-50 breaths/min in the 1st few weeks of life and usually <60 breaths/min in the 1st few days of life.

Respiratory control abnormalities can cause the child to breathe at a low rate or periodically. Mechanical abnormalities produce compensatory changes that are generally directed at altering minute ventilation to maintain alveolar ventilation. Decreases in lung compliance require increases in muscular force and breathing rate, leading to variable increases in chest wall retractions and nasal flaring. The respiratory excursions of children with restrictive disease are shallow. An expiratory grunt is common as the child attempts to raise the functional residual capacity (FRC) by closing the glottis at the end of expiration. Children with obstructive disease might take slower, deeper breaths (Chapter 365). When the obstruction is extrathoracic (from the nose to the mid-trachea), inspiration is more prolonged than expiration, and an inspiratory stridor can usually be heard. When the obstruction is intrathoracic, expiration is more prolonged than inspiration, and the patient often has to make use of accessory expiratory muscles. Intrathoracic obstruction results in air trapping and, therefore, a larger residual volume and, perhaps, greater functional residual capacity.

Lung percussion has limited value in small infants because it cannot discriminate between noises originating from tissues that are close to each other. In adolescents and adults, percussion is usually dull in restrictive lung disease, with a pleural effusion, pneumonia, and atelectasis, but it is tympanitic in obstructive disease (asthma, pneumothorax).

Auscultation confirms the presence of inspiratory or expiratory prolongation and provides information about the symmetry and quality of air movement. In addition, it often detects abnormal or adventitious sounds such as stridor (a predominant inspiratory monophonic noise), crackles (or rales) (high-pitched, interrupted sounds found during inspiration and more rarely during early expiration, which denote opening of previously closed air spaces), or wheezes (musical, continuous sounds usually caused by the development of turbulent flow in narrow airways) (Table 366-1). Digital clubbing is a sign of chronic hypoxia and chronic lung disease (Fig. 366-1) but may be due to nonpulmonary etiologies (Table 366-2).

Figure 366-1 Finger clubbing can be measured in different ways. The ratio of the distal phalangeal diameter (DPD) over the interphalangeal diameter (IPD), or the phalangeal depth ratio, is <1 in normal subjects but increases to >1 with finger clubbing. The DPD/IPD can be measured with calipers or, more accurately, with finger casts. The hyponychial angle can be measured from lateral projections of the finger contour on a magnifying screen and is usually <180 degrees in normal subjects but >195 degrees in patients with finger clubbing. For bedside clinical assessment, the Schamroth sign is useful. The dorsal surfaces of the terminal phalanges of similar fingers are placed together. With clubbing, the normal diamond-shaped aperture or “window” at the bases of the nail beds disappears, and a prominent distal angle forms between the ends of the nails. In normal subjects, this angle is minimal or nonexistent.

(From Chernick V, Boat TF: Kendig’s disorders of the respiratory tract in children, ed 6, Philadelphia, 1998, WB Saunders.)

Table 366-1 LUNG SOUND NOMENCLATURE

From Cugell DW: Lung sound nomenclature, Am Rev Respir Dis 136:1016, 1987, with permission; from Chernick V, Boat TF: Kendig’s disorders of the respiratory tract in children, ed 6, Philadelphia, 1998, WB Saunders, p 97.

Blood Gas Analysis

An arterial blood gas analysis is probably the single most useful rapid test of pulmonary function. Although this analysis does not specify the cause of the condition or the specific nature of the disease process, it can give an overall assessment of the functional state of the respiratory system and clues about the pathogenesis of the disease. Because the detection of cyanosis is influenced by skin color, perfusion, and blood hemoglobin concentration, the clinical detection by inspection is an unreliable sign of hypoxemia. Arterial hypertension, tachycardia, and diaphoresis are late, and not exclusive, signs of hypoventilation.

Blood gas exchange is evaluated most accurately by the direct measurement of arterial PO₂, PCO₂, and pH (Chapters 95.3 and 365). The blood specimen is best collected anaerobically in a heparinized syringe containing only enough heparin solution to displace the air from the syringe. The syringe should be sealed, placed in ice, and analyzed immediately. Although these measurements have no substitute in many conditions, they require arterial puncture and have been replaced to a great extent by noninvasive monitoring, such as capillary samples and/or oxygen saturation.

The age and clinical condition of the patient need to be taken into account when interpreting blood gas tensions. With the exception of neonates, values of arterial PO₂ <85 mm Hg are usually abnormal for a child breathing room air at sea level. Calculation of the alveolar-arterial oxygen gradient is useful in the analysis of arterial oxygenation, particularly when the patient is not breathing room air or in the presence of hypercarbia. Values of arterial PCO₂ >45 mm Hg usually indicate hypoventilation or a severe ventilation-perfusion mismatch, unless they reflect respiratory compensation for metabolic alkalosis (Chapter 52).

Transillumination of the Chest

In infants up to at least 6 months of age, a pneumothorax can often be diagnosed by transilluminating the chest wall using a fiberoptic light probe. Free air in the pleural space often results in an unusually large halo of light in the skin surrounding the probe. Comparison with the contralateral chest is often very helpful in interpreting findings. This test is unreliable in older patients and in those with subcutaneous emphysema or atelectasis.

Radiographic Techniques

Pulmonary Function Testing

The measurement of respiratory function in infants and young children can be difficult because of the lack of cooperation. Attempts have been made to overcome this limitation by creating standard tests that do not require the patient’s active participation. Respiratory function tests still provide only a partial insight into the mechanisms of respiratory disease at early ages.

Whether restrictive or obstructive, most forms of respiratory disease cause alterations in lung volume and its subdivisions (Chapter 365). Restrictive diseases typically decrease total lung capacity (TLC). TLC includes residual volume, which is not accessible to direct determinations. It must therefore be measured indirectly by gas dilution methods or, preferably, by plethysmography. Restrictive disease also decreases vital capacity (VC). Obstructive diseases produce gas trapping and thus increase residual volume and FRC, particularly when these measurements are considered with respect to TLC.

Airway obstruction is most commonly evaluated from determinations of gas flow in the course of a forced expiratory maneuver. The peak expiratory flow is reduced in advanced obstructive disease. The wide availability of simple devices that perform this measurement at the bedside makes it useful for assessing children who have airway obstruction. Evaluation of peak flows requires a voluntary effort, and peak flows may not be altered when the obstruction is moderate or mild. Other gas flow measurements require that the child inhale to TLC and then exhale as far and as fast as possible for several seconds. Cooperation and good muscle strength are therefore necessary for the measurements to be reproducible. The forced expiratory volume in 1 sec (FEV₁) correlates well with the severity of obstructive diseases. The maximal midexpiratory flow rate, the average flow during the middle 50% of the forced vital capacity (FVC), is a more reliable indicator of mild airway obstruction. Its sensitivity to changes in residual volume and vital capacity, however, limits its use in children with more severe disease. The construction of flow-volume relationships during the FVC maneuvers overcomes some of these limitations by expressing the expiratory flows as a function of lung volume (Chapter 365).

A spirometer is used to measure VC and its subdivisions and expiratory (or inspiratory) flow rates (see Fig. 365-1). A simple manometer can measure the maximal inspiratory and expiratory force a subject generates, normally at least 30 cm H₂O, which is useful in evaluating the neuromuscular component of ventilation. Expected normal values for VC, FRC, TLC, and residual volume are obtained from prediction equations based on body height.

Flow rates measured by spirometry usually include the FEV₁ and the maximal midexpiratory flow rate. More information results from a maximal expiratory flow-volume curve, in which expiratory flow rate is plotted against expired lung volume (expressed in terms of either VC or TLC). Flow rates at lung volumes <~75% VC are relatively independent of effort. Expiratory flow rates at low lung volumes (<50% VC) are influenced much more by small airways than are flow rates at high lung volumes (FEV₁). The flow rate at 25% VC (V₂₅) is a useful index of small airway function. Low flow rates at high lung volumes associated with normal flow at low lung volumes suggest upper airway obstruction (Chapter 365).

Airway resistance (R_AW) is measured in a plethysmograph, or, alternatively, the reciprocal of R_AW, airway conductance (G_AW), may be used. Because airway resistance measurements vary with the lung volume at which they are taken, it is convenient to use specific airway resistance, SR_AW (SR_AW = R_AW/lung volume), which is nearly constant in subjects >6 yr old (normally <7 sec/cm H₂O).

The diffusing capacity for carbon monoxide (DLCO) is related to oxygen diffusion and is measured by rebreathing from a container having a known initial concentration of carbon monoxide or by using a single-breath technique. Decreases in DLCO reflect decreases in effective alveolar capillary surface area or decreases in diffusibility of the gas across the alveolar-capillary membrane. Primary diffusion abnormalities are unusual in children; therefore, this test is most commonly employed in children with rheumatologic or autoimmune diseases and in children exposed to toxic drugs to the lungs (e.g., oncology patients) or chest wall radiation. Regional gas exchange can be conveniently estimated with the perfusion-ventilation xenon scan. Determining arterial blood gas levels also discloses the effectiveness of alveolar gas exchange.

Pulmonary function testing, although rarely resulting in a diagnosis, is helpful in defining the type of process (obstruction, restriction) and the degree of functional impairment, in following the course and treatment of disease, and in estimating the prognosis. It is also useful in preoperative evaluation and in confirmation of functional impairment in patients having subjective complaints but a normal physical examination. In most patients with obstructive disease, a repeat test after administering a bronchodilator is warranted.

Most tests require some cooperation and understanding by the patient, and interpretation is greatly facilitated if the test conditions and the patient’s behavior during the test are known. Infants and young children who cannot or will not cooperate with test procedures can be studied in a limited number of ways, which often require sedation. Flow rates and pressures during tidal breathing, with or without transient interruption of the flow, may be useful to assess some aspects of airway resistance or obstruction and to measure compliance of the lungs and thorax. Expiratory flow rates can be studied in sedated infants with passive compression of the chest and abdomen with a rapidly inflatable jacket. Gas dilution or plethysmographic methods can also be used in sedated infants to measure FRC and R_AW.

Microbiology: Examination of Lung Secretions

The specific diagnosis of infection in the lower respiratory tract depends on the proper handling of an adequate specimen obtained in an appropriate fashion. Nasopharyngeal or throat cultures are often used but might not correlate with cultures obtained by more-direct techniques from the lower airways. Sputum specimens are preferred and are often obtained from patients who do not expectorate by deep throat swab immediately after coughing or by saline nebulization. Specimens can also be obtained directly from the tracheobronchial tree by nasotracheal aspiration (usually heavily contaminated), by transtracheal aspiration through the cricothyroid membrane (useful in adults and adolescents but hazardous in children), and in infants and children by a sterile catheter inserted into the trachea either during direct laryngoscopy or through a freshly inserted endotracheal tube. A specimen can also be obtained at bronchoscopy. A percutaneous lung tap or an open biopsy is the only way to obtain a specimen absolutely free of oral flora.

A specimen obtained by direct expectoration is usually assumed to be of tracheobronchial origin, but often, especially in children, it is not from this source. The presence of alveolar macrophages (large mononuclear cells) is the hallmark of tracheobronchial secretions. Nasopharyngeal and tracheobronchial secretions can contain ciliated epithelial cells, which are more commonly found in sputum. Nasopharyngeal and oral secretions often contain large numbers of squamous epithelial cells. Sputum can contain both ciliated and squamous epithelial cells.

During sleep, mucociliary transport continually brings tracheobronchial secretions to the pharynx, where they are swallowed. An early-morning fasting gastric aspirate often contains material from the tracheobronchial tract that is suitable for culture for acid-fast bacilli.

The absence of polymorphonuclear leukocytes in a Wright-stained smear of sputum or bronchoalveolar lavage (BAL) fluid containing adequate numbers of macrophages may be significant evidence against a bacterial infectious process in the lower respiratory tract, assuming that the patient has normal neutrophil counts and function. Eosinophils suggest allergic disease. Iron stains can reveal hemosiderin granules within macrophages, suggesting pulmonary hemosiderosis. Specimens should also be examined by Gram stain. Bacteria within or near macrophages and neutrophils can be significant. Viral pneumonia may be accompanied by intranuclear or cytoplasmic inclusion bodies visible on Wright-stained smears, and fungal forms may be identifiable on Gram or silver stains.

Exercise Testing

Exercise testing (Chapter 417.5) is a more-direct approach for detecting diffusion impairment as well as other forms of respiratory disease. Exercise is a strong provocateur of bronchospasm in susceptible patients, so exercise testing can be useful in the diagnosis of patients with asthma that is only apparent with activity. Measurements of heart and respiratory rate, minute ventilation, oxygen consumption, carbon dioxide production, and arterial blood gases during incremental exercise loads often provide invaluable information about the functional nature of the disease. Often a simple assessment of the patient’s exercise tolerance in conjunction with other, more static forms of respiratory function testing can allow a distinction between respiratory and nonrespiratory disease in children.

Sleep Studies

The sleep state has an important influence on respiratory function at all ages. Polysomnographic studies are often helpful for diagnosing airway obstruction during sleep, when abnormalities of central respiratory control, muscular disorders, or respiratory complications from gastroesophageal reflux (GER) are suspected. Polysomnography is now considered the gold standard test for obstructive sleep apnea or hypoventilation during sleep. pH probe studies are indicated and are added to such sleep studies when GER is suspected. In these studies, a pH probe is placed in the esophagus and prolonged (usually over several hours) monitoring is undertaken (Chapter 315). These studies, which usually include the simultaneous assessment of ventilatory effort, airway gas flow, gas exchange, and sleep state, are also useful in the diagnosis and management of airway and respiratory control disorders and nocturnal hypoxemia and hypercapnia in children with chronic respiratory disease (Chapter 365).

Airway Visualization and Lung Specimen–Based Diagnostic Tests