Common Respiratory Disorders

Laryngotracheobronchitis (Croup)

Croup is the most common cause of acute upper airway obstruction in an otherwise healthy child (see Chapter 60 ). This viral infection (parainfluenza, influenza, adenovirus) produces swelling and edema of the tissues in the upper airway, particularly in the immediate subglottic region. Croup occurs most commonly in young infants and children between the ages of 3 months and 3 years. Children usually have a few days' history of an upper respiratory infection followed by the development of hoarseness, a croupy cough, and possibly stridor.^[165] The degree of respiratory distress and the child's ability to compensate

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Infants are initially treated with mist and aerosolized racemic epinephrine to reduce local mucosal swelling.^[166] The use of steroids is both common and controversial.^[123] Intubation is required when the infant can no longer sustain the necessary work of breathing. The child is intubated with the smallest possible ETT (usually 3.0 mm in a child younger than 2 years or 3.5 mm in a child aged 2 to 4 years) that will permit suctioning of secretions. Spontaneous resolution in 3 to 7 days is common. In my experience, the average duration of intubation is 4 to 5 days. As the trachea grows, laryngotracheobronchitis becomes an uncommon cause of significant airway obstruction in children older than 4 years.

Epiglottitis

Epiglottitis is an inflammation of the mucosa of the supraglottic structures that is usually caused by Haemophilus influenzae type B.^[167] It is a true pediatric emergency because its rapid progression has the potential for unpredictable and fatal airway obstruction. Restoration of a secure airway is the first priority. Epiglottitis is usually easily differentiated from laryngotracheobronchitis in that patients with epiglottitis are generally older (4 to 6 years), there is rarely an antecedent upper respiratory illness, and the child is in a quite toxic condition with the fulminant onset of fever and respiratory distress. Expectant intubation under anesthesia is the most common treatment until antibiotic therapy (ampicillin and chloramphenicol or ceftriaxone) is initiated and signs of systemic toxicity subside. The incidence of epiglottitis is dependent on contact with H. influenzae, which occurs most commonly in the early school-aged population.^[168] The introduction of H. influenzae vaccine has dramatically decreased the incidence of this disease, as well as that of other H. influenzae processes.^[169]

Bronchiolitis

Bronchiolitis is an acute viral infection of the lower respiratory tract that frequently occurs in the first 2 years of life, when small airways have the lowest specific conductance. The signs and symptoms are air trapping, wheezing, mild to moderate systemic hypoxemia, and a considerable increase in the work of breathing because of increased airway resistance. The cause is viral, usually attributed to respiratory syncytial virus.^[170] Bronchiolitis is epidemic in nature and variable in severity.

Although the disease is self-limited, patients at high risk of respiratory failure include infants and young children with a history of prematurity, chronic lung disease, or congenital heart disease. In neonates, apnea is often the first sign of decompensation, and it frequently occurs before significant hypercapnia. Clinical signs of fatigue are often more important than ABG sampling in determining whether mechanical ventilation is indicated. Therapy is primarily supportive, with endotracheal intubation and mechanical ventilation when the child can no longer support gas exchange.^[171]

Ribavirin is a virostatic drug available for use in children with respiratory syncytial viral infection. Infants and young children with complicated congenital heart disease, underlying immunosuppressive disease, or multiple congenital anomalies who acquire respiratory syncytial viral disease and are at high risk of serious complications should be considered for ribavirin aerosol therapy. Because of concern about its safety, benefit, and cost, definitive recommendations for ribavirin therapy are not possible.^[170]

Status Asthmaticus

Asthma, a disease of airway hyperreactivity, is the most common chronic respiratory disorder of childhood and is often the most frequent admission diagnosis to a pediatric medical service. Acute attacks are generally associated with intercurrent viral infections, allergen exposure, stress, or noncompliance with therapy.^[172]

The chronic treatment of asthma emphasizes a stepwise approach using inhaled aerosolized β-agonists, cromolyn/nedocromil, leukotriene pathway modifiers, and inhaled glucocorticoids.^[173] Of concern, the number of asthmatic patients and the mortality rate associated with asthma have been increasing. High mortality is associated with a number of risk factors: teen age, black race, history of previous life-threatening episodes, hospitalization within the last year, poor long-term medical care, and psychological and psychosocial problems.

Most episodes of status asthmaticus respond to emergency department management with oxygen, nebulized/inhaled β-agonists, anticholinergic agents, and intravenous steroids.^[174] A few children, however, fail to improve or even worsen despite this therapy. Signs of respiratory failure develop, including tachypnea and tachycardia, very poor aeration with a prolonged expiratory phase, marked retractions, nasal flaring, increased pulsus paradoxus, anxiety, or depressed mental status. Despite the increased minute ventilation, PaCO₂ is either normal or elevated, and moderate to severe hypoxemia is present. Treatment of this impending respiratory failure is to maximize conservative therapy and start an intravenous terbutaline infusion beginning at a rate of 0.1 μg/kg/min and increasing until clinical improvement occurs or until the heart rate exceeds 180 to 200 beats/min. If the patient is being treated with aminophylline, levels should be closely monitored. It is important to note that both phosphodiesterase inhibitors and adrenergic agonists share the serious side effects of increased myocardial oxygen consumption, potential myocardial ischemia, and ventricular arrhythmias; hence, it is important to prevent hypoxia and closely monitor with continuous ECG. Children tolerate these drug groups better than their adult counterparts do, most likely because children have relatively normal coronary arteries and better myocardial reserve. Inhaled heliox (a 70:30 helium-oxygen mixture) is about one third as dense as room air and may decrease the work of breathing in some asthmatics. It may not be feasible if high oxygen concentrations are required to prevent hypoxemia. Intravenous magnesium sulfate acts as a smooth muscle relaxant and may reduce bronchoconstriction. When administered as an infusion at 25 to 40 mg/kg (maximum of 2 g) over a 20-minute period, it has been demonstrated to improve pulmonary function. Hypotension, decreased reflexes, and drowsiness are recognized side effects.^[175]

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Tracheal intubation and mechanical ventilation are considered a last resort. PaCO₂ values in excess of 70 or 80 mm Hg are tolerated as long as the patient is cardiovascularly and neurologically stable.^[176] Intubation is only rarely required in a pediatric patient with asthma and is avoided if possible because the ETT serves as an irritant in the airway and may cause further bronchoconstriction. In addition, mechanical ventilation is usually inefficient in a patient with small airways disease, and the complications of barotrauma in all its forms are common. Inhaled anesthetics such as halothane and isoflurane have been used as bronchodilators in mechanically ventilated patients with asthma and those with severe respiratory failure who are unresponsive to maximal conventional therapy.^[177] ECMO could also be used in these patients if gas exchange cannot be achieved with conventional ventilators.

Cystic Fibrosis

Cystic fibrosis is a fatal autosomal recessive disease carried on chromosome 7. Although it is manifested as pancreatic, hepatic, pulmonary, GI, and reproductive abnormalities, 90% of the reported morbidity and mortality is pulmonary. ^[178] The pulmonary pathologic process is severe obstructive disease with bronchiectasis, emphysema, and ultimately, terminal respiratory failure.

Survival has improved dramatically over the past 30 years. More than a third of patients survive beyond the age of 30 years.^[179] This change reflects improved antibiotic therapy, nutritional adjuncts, and a more aggressive approach to the complications of the disease. This aggressive approach often involves extensive surgical procedures such as pleural stripping and pulmonary lobectomy. The success of these procedures necessitates a program of careful preoperative, intraoperative, and postoperative pulmonary care, which can often require a lengthy ICU admission for respiratory support and management. Lung transplants are being offered to these patients with chronic respiratory failure.^[180]

Bronchopulmonary Dysplasia

BPD is a form of chronic lung disease seen in young patients who survive severe neonatal lung disease. The cause is uncertain, but patients usually share the common history of prematurity, hyaline membrane disease, and a requirement for prolonged aggressive respiratory support with high levels of inflating and distending pressure and high FIO₂ values. Children with BPD have decreased dynamic compliance, increased airway resistance, increased physiologic dead space, and markedly increased work of breathing. On examination, these children are hyperinflated with retractions, nasal flaring, and wheezing. Chest radiographs show large lung volumes, fibrosis, and cystic and atelectatic areas. ABG analysis shows chronic hypercapnia and varying degrees of hypoxemia.^{[181] [182]}

Therapy for BPD includes maximal nutritional supplementation to support the large energy expenditure for the increased work of breathing, in addition to varying degrees of respiratory support. Some children have been treated with chronic mechanical ventilation and chronic increased ambient oxygen. Diuretics and bronchodilators are often adjunctive therapies. Most children are long-term survivors with subjectively normal pulmonary function. However, there is evidence^{[183] [184]} of chronic physiologic changes in this population. During the first years of life, any extraneous pulmonary infection or embarrassment may necessitate acute or chronic intensive respiratory support or may in fact prove to be a fatal event.

Much effort is being made to prevent the development of BPD. Because the trauma of mechanical ventilation on an immature lung is identified as the major cause, alternative modes of ventilatory support are being evaluated, including exogenous surfactant, high-frequency ventilation (especially HFOV),^[151] ECMO, and liquid ventilation.^{[181] [185]}

Sleep Apnea

Normal ventilation during sleep depends on normal upper airway anatomy and a number of intact reflexes, including the central response to hypercapnia and hypoxia, the response to airway irritation, and dynamic phasic contraction of the pharyngeal and hypopharyngeal muscles, all of which help maintain a patent airway. Sleep spnea usually results from an abnormality in one or more of these normal protective responses.

In infancy, central sleep apnea is not uncommon. Numerous potential causes have been postulated, but perhaps the most attractive is immaturity of the medullary chemoreceptors. Central sleep apnea can be complete, as in the Ondine curse, or it may be some lesser degree of hypoventilation related to the group of disorders causing sudden infant death syndrome (SIDS). Treatment consists of respiratory stimulants (theophylline), cardiorespiratory monitoring during sleep, and in complete sleep apnea, tracheotomy and nighttime mechanical ventilation.^[186]

Obstructive sleep apnea can occur in any pediatric age group. It can be associated with an identifiable anatomic disorder (e.g., tonsils, adenoids, and Pierre Robin syndrome) or with the more obscure dynamic abnormalities of lax pharyngeal musculature. Signs and symptoms include loud snoring, obstructive episodes with constant arousal, behavior disorders associated with sleep deprivation, and cor pulmonale. The diagnosis is made by the history, ECG, and formal sleep studies.

Treatment includes any maneuver that helps remove or bypass the obstruction. Tonsillectomy and adenoidectomy are generally performed to maximize the patent airway. Rarely does a child require a tracheostomy for definitive therapy.

Foreign Body Aspiration

Foreign body aspiration is a relatively common and often catastrophic event in children. Although it can occur at any age, the peak incidence is 6 months to 3 years. Materials aspirated range from vegetable matter (peanuts) and other foodstuffs (hot dogs) to coins and small pieces of toys; of interest to the clinician is that most of these objects are radiolucent. The symptoms noted by the physician are a function of both the location of the foreign body within the airway and the time of initial evaluation. Acute symptoms may include total airway obstruction, stridor, wheezing, or acute onset of

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Treatment is controversial. There is much argument on the comparative efficacy and safety of abdominal thrusts, Heimlich's maneuver, and back slaps, all of which are reserved for acute upper airway obstruction in which no air movement is occurring. Treatment of less acute or lower airway foreign body aspiration includes bronchoscopy, postural drainage, chest physical therapy, bronchodilators, and surgical removal.^[187]

Upper Airway Obstruction and Meningomyelocele

Stridor from bilateral vocal cord abductor paralysis is a reported complication of myelodysplasia. The vocal cord paralysis is secondary to brainstem abnormalities. Children with meningomyelocele have associated Arnold-Chiari malformations with a caudally displaced medulla, abnormally long cranial nerve tracts, and abnormal arterioarchitecture of the brainstem.

The vocal cord paralysis may be secondary to either pressure on the brainstem (i.e., with hydrocephalus) or focal infarcts. Treatment entails decompressing any degree of hydrocephalus and, if the paralysis persists, performing a high cervical decompression. Despite these surgical maneuvers, some children require a tracheotomy for long-term care.