The primary function of the respiratory system is to provide adequate and adaptive gas exchange with a supply of oxygen to the body and removal of carbon dioxide. Illness can disturb this function by affecting 1 or more of the following: the central control of breathing, the respiratory pump comprising the chest cage and respiratory muscles, the small and large airways, and the pulmonary parenchyma. Nonrespiratory functions of the lung include production and regulation of surfactant, defense against infections, effective mucociliary clearance, participation in water and fluid balances, filtering of blood cells and emboli, and elimination of volatile substances.
Respiratory illness in children usually presents with clinical symptoms and signs that offer important diagnostic information. A clinical examination of the respiratory system should including inspection, palpation/percussion, and auscultation.
The thoracic cage is vital for the efficient bellows action of the respiratory pump. Congenital or acquired malformations of the chest wall can, therefore, impact considerably on lung volume and function. Congenital anomalies involve the sternum with concavity (pectus excavatum, see Fig. 498-1) or protrusion (pectus carinatum), the spine (eg, scoliosis, kyphosis), or the ribs themselves, sometimes in combination with an overall small thoracic cage (eg, Jeune syndrome or cerebrocostomandibular syndrome).
Patient with pectus excavatum.
Acquired deformations of the chest wall can be secondary to neuromuscular weakness (eg, flattening of the chest in children with spinal muscular atrophy) or reflect underlying chronic respiratory diseases. The Harrison sulcus, for example, is a groove along the lower ribs corresponding to the attachment of the diaphragm that develops after prolonged increase in the work of breathing. A secondary pectus excavatum might develop after longstanding upper airway obstruction. Chronic hyperinflation (eg, in asthma or cystic fibrosis) can lead to a barrel chest with increase of the anterior-posterior diameter of the thorax.
The respiratory rate (breaths per minute) is essential for assessing the respiratory function of children. Normal ranges are dependent on age, weight, body temperature, wakefulness, and the activity level of the child. The respiratory rate is counted by observing chest and abdominal movements or by listening to breaths with a stethoscope. The respiratory rate can be calculated by counting breaths for 15 or 30 seconds and multiplying the resulting number by 4 or 2, respectively. Table 498-1 shows reference values for afebrile children from birth to 18 years of age.
TABLE 498-1NORMAL RANGES OF RESPIRATORY RATES IN CHILDREN FROM BIRTH TO 18 YEARS |Favorite Table|Download (.pdf) TABLE 498-1NORMAL RANGES OF RESPIRATORY RATES IN CHILDREN FROM BIRTH TO 18 YEARS
|Age ||1st Percentile ||10th–90th (50th) Percentile ||99th Percentile |
|0–2 months ||20 ||27–47 (35) ||60 |
|3–5 months ||20 ||25–42 (31) ||55 |