PREDISPOSING FACTORS

Respiratory function must equate with metabolic demands. Oxygen consumption in the infant is approximately 7 ml/kg per min (compared with 3–4 ml/kg per min in the older child and adult). Fever, illness and restlessness dramatically increase demands; during periods of apnoea or respiratory depression, PaCO₂ rises at twice the rate of older children and adults. Respiratory reserve is reduced in infants and neonates due to the following factors.

CLINICAL PRESENTATION

Respiratory distress is manifested by tachypnoea, distortion of the chest wall (i.e. sternal and rib retraction, recession of intercostal, subcostal and suprasternal spaces) and use of accessory muscles (e.g. flaring of alae nasi and use of neck muscles).

In young infants, lethargy, pallor, apnoea, bradycardia and hypotension may be the first signs of hypoxia. The physiological anaemia of infancy may delay recognition of cyanosis, and major signs are those of CNS and cardiovascular depression. Increased work of breathing, marked by tachypnoea and chest-wall retraction, is poorly sustained; bradypnoea and apnoea are evidence of respiratory fatigue. Expiratory ‘grunting’ is a sign of respiratory distress that represents an attempt to maintain a positive expiratory airway pressure to prevent airway closure and alveolar collapse, the equivalent of pursed-lip breathing in the adult.

The older child with acute hypoxia, like the adult, demonstrates tachycardia, hypertension, mental confusion and restlessness prior to CNS and cardiovascular depression. Sweating occurs with CO₂ retention – a feature lacking in the newborn.

In the newborn, the effects of hypoxia and acidosis may be compounded by the development of pulmonary hypertension and reversion to a transitional circulation, with right-to-left shunting through a patent ductus arteriosus and foramen ovale. If untreated, increasing hypoxaemia, progressive acidosis and death may occur.

Conventional clinical examination of the chest should be performed. It is, however, of limited value in the neonate, as breath sounds may be transmitted uniformly through the chest, even in the presence of tension pneumothorax, lobar collapse or endobronchial intubation. The chest X-ray is an essential part of the assessment.

AETIOLOGY

Acute respiratory failure may result from upper or lower airway obstruction, alveolar disease, pulmonary compression, neuromuscular disease or injury (Table 98.1). Upper respiratory tract obstruction is discussed in Chapter 97.

Table 98.1 Causes of respiratory insufficiency in infancy and childhood

TRACHEOMALACIA, TRACHEAL STENOSIS AND VASCULAR COMPRESSION

Instability of the tracheal wall (tracheomalacia) is most commonly associated with oesophageal atresia, tracheo-oesophageal fistula and various vascular anomalies. The most common causes of vascular compression are a double aortic arch and the complex of a right-sided aortic arch, left ductus arteriosus and an aberrant left subclavian artery. These produce a true vascular ring, with encirclement of the trachea and oesophagus. Anterior tracheal compression may also be due to an anomalous innominate artery. Lower tracheomalacia or tracheal stenosis may occur in association with an anomalous left pulmonary artery (pulmonary artery sling). The problem may extend to the major bronchi (bronchomalacia). Tracheomalacia and bronchomalacia also occur as isolated airway anomalies. In this situation, the severity of dynamic airway obstruction is aggravated by any condition that results in reduced lung compliance.

Division of the vascular ring and ligation or repositioning of the aberrant vessel, while removing the cause of the obstruction, do not immediately re-establish normal airway dimensions or stability. Although severity of symptoms may be alleviated by surgery, problems may persist for some years. Tracheomalacia may sometimes be stabilised by a prolonged period of nasotracheal intubation or tracheostomy with continuous positive airway pressure (CPAP). Tracheopexy, which suspends the anterior tracheal wall from the posterior sternal surface and great vessels, is occasionally useful. A slide tracheoplasty may be required to correct tracheal stenosis associated with complete tracheal rings.³ A range of stenting devices have also been developed for complex airways and employed with mixed success.

MECONIUM ASPIRATION SYNDROME

Meconium aspiration is seen in 0.3% of live births, and is most common in term or postterm infants. There is usually a history of fetal distress in labour, or prolonged and complicated delivery. Asphyxia during labour results in the expulsion of meconium into the liquor. With the first few breaths, material in the upper airway (i.e. amniotic fluid, meconium, vernix and squames) is inhaled, obstructing small airways and producing atelectasis and obstructive emphysema. Meconium also causes a chemical pneumonitis and surfactant abnormalities. During recovery, the aspirated material is absorbed and phagocytosed.

Clinical signs include tachypnoea, retraction and cyanosis. The chest may become hyperexpanded and pneumomediastinum or pneumothorax is a frequent complication. Pulmonary hypertension and persistent fetal circulation are common.

The chest X-ray confirms the diagnosis, with coarse mottling and streakiness radiating from the hila. Lungs are overexpanded, with flattened diaphragms and an increase in the chest anteroposterior diameter. The condition is largely preventable if the airway can be aspirated rapidly and completely following delivery of the head and before the first breath.

Most of these infants require oxygen therapy. Severely affected infants require controlled mechanical ventilation (CMV), which may be difficult because of the high pressures required, the non-uniformity of ventilation, and danger of pneumothorax. Improved outcomes are now achieved using surfactant (may cause transient deterioration), inhaled nitric oxide and high-frequency oscillation.⁴ Extracorporeal membrane oxygenation (ECMO) is also effective in those centres that have the facility, although its use has declined since the introduction of the above therapies. Cerebral effects of severe intrapartum asphyxia contribute to overall morbidity and mortality.

CONGENITAL CYSTIC ADENOMATOID MALFORMATION

Congenital cystic adenomatoid malformation (CCAM) of the lung results from abnormal mesenchymal proliferation and failure of maturation of bronchiolar structures early in gestation. The result is multiple lung cysts, usually within a single lobe. CCAM is often diagnosed on antenatal ultrasound. Other cases present with respiratory distress due to obstruction whilst others present with infection in the cysts and recurrent lobar pneumonia. Some cases are diagnosed incidentally on chest radiographs taken for another reason. Some cases are associated with renal dysplasia. Even asymptomatic infants are at risk of cyst expansion or infection and lobectomy is the treatment of choice for all cases.

LOBAR EMPHYSEMA

Congenital lobar emphysema is characterised by overdistension of a pulmonary lobe caused by air trapping. Most cases present in the first month of life, with tachypnoea, wheezing, grunting and cough. Signs include hyperresonance, decreased air entry and deviation of the trachea and heart away from the affected lobe. There may be asymmetry of the chest due to bulging of the affected hemithorax. Cyanosis may be associated with periods of increased respiratory distress. There may be associated cardiovascular abnormalities, rib cage abnormalities or renal dysplasia.

Radiologically, the affected lobe is overdistended with compression and deviation of the surrounding structures. The pathogenesis is unknown in over 50%, 25% have localised bronchial cartilaginous dysplasia, and the remainder have obstruction of a lobar bronchus from a mucous plug, redundant mucosa, aberrant vessels or localised stenosis. Lobectomy is the definitive surgical treatment. Care must be taken with positive airway pressure because of the risk of further overdistension.

ASPIRATION PNEUMONIA

In the newborn, aspiration may result from pharyngeal incoordination or lack of protective reflexes, due to prematurity, birth asphyxia or intracranial haemorrhage. It is particularly likely to occur with abnormalities of the alimentary tract, such as oesophageal atresia, tracheo-oesophageal fistula and oesophageal reflux. Large and small airway obstruction and pneumonia may occur.

HYALINE MEMBRANE DISEASE

This is due to deficiency of lung surfactant. Predisposing factors are prematurity, maternal diabetes and intranatal asphyxia. Postnatal hypoxia and acidosis also inhibit surfactant production. Lack of surfactant results in alveolar instability, atelectasis, intrapulmonary shunting and increased work of breathing.

Clinical signs appear shortly after birth and consist of tachypnoea, chest-wall retraction, expiratory grunting and a progressive increase in oxygen requirements. The chest X-ray reveals a reticulogranular pattern (ground-glass appearance) with air bronchograms. In uncomplicated cases, the disease is self-limiting and resolves in 4–5 days. Respiratory failure may require increasing inspired oxygen concentrations (FiO₂), CPAP, intermittent mandatory ventilation (IMV) or CMV. CPAP is known to improve oxygenation, the pattern and regularity of respiration, retard the progression of the disease and reduce morbidity, particularly with early application in the extremely preterm infant. In infants with persistent pulmonary hypertension, transitional circulation and requiring high airway pressures, the use of inhaled nitric oxide and high-frequency oscillatory ventilation are beneficial.

Instillation of surfactant into the trachea has been shown to improve oxygenation and compliance (despite some initial deterioration) and reduce the risk of pneumothorax, early mortality and morbidity.^5–8 Two types of surfactant are used: synthetic (Exosurf), and bovine (Survanta) or porcine (Curosurf).

BRONCHOPULMONARY DYSPLASIA

Bronchopulmonary dysplasia (BPD), or chronic lung disease, may occur in survivors of neonatal lung disease. Its occurrence correlates with lung immaturity, high airway pressures and barotrauma. The lung architecture is abnormal with widespread fibrosis and cystic changes. There is often a reactive component to the airway disease that may be responsive to bronchodilator and anti-inflammatory therapy, such as steroids. It is a cause of chronic respiratory failure in infancy, and in severe cases progresses to cor pulmonale and death in the first 2 years of life. Prolonged low-flow home oxygen therapy may be necessary to reduce the risk of pulmonary hypertension. Superimposed bacterial and viral infection may exacerbate chronic respiratory failure and lead to further lung injury.

PNEUMONIA

Perinatal pneumonia may occur as a result of transplacental spread of a maternal infection, prolonged rupture of membranes, passage through an infected birth canal or cross-infection in the nursery. The immunoparetic state of the newborn and the need for invasive procedures increase the risk.

Clinical and radiological features may be indistinguishable from hyaline membrane disease. Antibiotics (e.g. penicillin and gentamicin) should be given until negative cultures exclude the diagnosis. The most common organisms include group B haemolytic Streptococcus, Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae and Staphylococcus aureus. Group B haemolytic streptococcal infection is frequently associated with septic shock and persistent fetal circulation. Failure to suspect group B haemolytic streptococcal infections (and hence treat promptly with penicillin) will result in poor outcome. Multiresistant staphylococcal and Gram-negative bacillary infections must be suspected in longer-stay patients in neonatal ICUs.

Most pneumonia in infants and young children is of viral origin. Viruses commonly implicated are respiratory syncytial virus (RSV), influenza A1, A2 and B, and parainfluenza types 1 and 3. Adenovirus and rhinovirus are less common causes. The spectrum of illness is wide. Many infants and children have cough, fever and tachypnoea, with X-ray evidence of patchy consolidation, all of which resolve rapidly. Occasionally, infants develop life-threatening respiratory illness with extensive pneumonic changes and marked necrosis. Permanent lung damage with bronchiolitis obliterans and pulmonary fibrosis may occasionally complicate severe adenoviral pneumonia in particular.

Bacterial pneumonia also occurs. Pneumococcal pneumonia is common and usually responds dramatically to appropriate antibiotic therapy. Staphylococcal pneumonia is relatively uncommon, but may result in life-threatening respiratory failure, and is often associated with complications (e.g. empyema, pneumatocele, tension pneumothorax and suppuration in other organs). Aspiration of an effusion may be useful for diagnostic purposes. Parapneumonic effusions (empyema) may require tube thoracostomy or video-assisted thoracoscopic drainage. Resolution of the effusion can be enhanced by the instillation of thrombolytic agents such as urokinase or tissue plasminogen activator.⁹ In severe cases with bronchopleural fistula, surgical resection of the necrotic area offers the best chance of survival.

Pneumonia due to Haemophilus influenzae may also occur and be associated with epiglottitis, meningitis, pericarditis or middle-ear disease. The prevalence of H. influenzae infection has reduced dramatically since the introduction of HiB immunisation.

Gram-negative pneumonia is seen mostly in infants with debilitating conditions who are hospitalised for prolonged periods. It is a particular risk for patients in ICUs with endotracheal or tracheostomy tubes. Other opportunistic infections, such as Pneumocystis jiroveci (formerly P. carinii), Candida albicans, Aspergillus and cytomegalovirus, may occur in immune deficiency states.

MASSIVE PULMONARY HAEMORRHAGE

This usually presents as acute cardiorespiratory collapse, accompanied by outpouring of bloodstained fluid from the trachea, mouth and nose. It is seen in association with severe birth asphyxia, hyaline membrane disease, congenital heart disease, erythroblastosis fetalis, coagulopathy and sepsis. Hypoxia is often a precipitating factor. The condition in the newborn is believed to represent haemorrhagic pulmonary oedema due to acute left ventricular failure. Treatment is that of the underlying condition with oxygenation, CMV and correction of any coagulation disturbance.

PULMONARY OEDEMA

Pulmonary oedema in the newborn period is due mostly to congenital heart disease, especially coarctation of the aorta, patent ductus arteriosus, critical aortic stenosis and, rarely, obstructed total anomalous pulmonary venous drainage. Pulmonary oedema due to circulatory overload may also occur in erythroblastosis fetalis, the placental transfusion syndrome, or as a result of inappropriate fluid therapy. Myocarditis is a further cause seen throughout infancy and childhood. Prolonged supraventricular tachycardia may result in ventricular dysfunction and biventricular failure, including pulmonary oedema.

In the newborn period, pulmonary oedema manifests as respiratory distress and feeding difficulty and specific features of congenital heart lesions may be evident. There is a spectrum of severity, from tachypnoea with a widened alveolar–arterial oxygen gradient to life-threatening respiratory failure requiring urgent support. Chest X-ray usually shows an enlarged heart (except in total anomalous pulmonary venous drainage) and a ground-glass appearance fanning out from the hilar regions.

PULMONARY HYPOPLASIA

This is seen most often in association with congenital diaphragmatic hernia, but bilateral pulmonary hypoplasia may also occur in association with renal agenesis or dysgenesis (Potter’s syndrome), in babies with severe Rhesus isoimmunisation, and in the presence of chronic amniotic fluid leak. It may also present as an isolated malformation. Unilateral hypoplasia can occur as an isolated anomaly or in association with cardiovascular defects.

DIAPHRAGMATIC HERNIA

Congenital diaphragmatic hernia (most commonly left-sided) results in respiratory failure, partly due to lung compression but mainly related to the associated pulmonary hypoplasia (both ipsilateral and contralateral). The degree of pulmonary hypoplasia is most severe in infants with absence of the diaphragm. The disturbance of pulmonary function ranges from mild to severe. In severe cases, life-threatening respiratory distress is present from birth, with cyanosis, intercostal retraction, mediastinal displacement, and poor or absent breath sounds on the affected side. The abdomen is usually scaphoid, due to much of its usual contents being in the chest. Chest X-ray shows loops of bowel in the affected hemithorax, with pulmonary compression and mediastinal displacement to the contralateral side.

Neonates presenting in the first 4 hours of life have major degrees of lung hypoplasia and have a mortality of 40% despite maximal supportive therapy. Those presenting after 4 hours of age should all survive. CMV may be complicated by tension pneumothorax and bronchopleural fistula on either side. Pulmonary hypertension with persistent fetal circulation and difficulties of CMV present major challenges. Many centres use ECMO or high-frequency ventilation in these infants. Nitric oxide is a useful pulmonary vasodilator in this condition.⁴ Prolonged ventilatory support is often required but the outlook for survivors is excellent.

PNEUMOTHORAX

Spontaneous pneumothorax may occur during the birth process in normal newborns, or secondary to hyaline membrane disease or meconium aspiration. Tension pneumothorax is particularly likely to occur when CMV is required in the presence of lung immaturity, lung hypoplasia, non-uniform lung disease (e.g. staphylococcal pneumonia) and diseases characterised by air trapping (e.g. meconium aspiration, bronchiolitis and asthma).

Tension pneumothorax should be suspected with any sudden deterioration of an infant on a ventilator. Classic clinical signs are evident in older children, but are of limited value in neonates. Circulatory embarrassment may be profound and rapidly progressive. Abdominal distension due to depression of the diaphragm and congestion of intra-abdominal organs, and unilateral chest hyperexpansion are useful signs. Transillumination of the thorax using a bright light source is a sensitive guide in newborn infants. A chest X-ray is mandatory, but should be preceded by needle aspiration or drainage if the infant’s condition is critical. Pre-existing pulmonary interstitial emphysema in one lung may also point to the likely side of the pneumothorax.

REPAIRED EXOMPHALOS OR GASTROSCHISIS

Complete repair of abdominal wall defects may cause marked elevation of intra-abdominal pressure when the intestines are then enclosed in a poorly developed peritoneal cavity. The diaphragm is elevated, compressing the lungs. In addition, compression of the inferior vena cava may lead to peripheral oedema, reduced cardiac output and oliguria (abdominal compartment syndrome). The associated paralytic ileus may further increase intra-abdominal pressure.

Disturbed lung function with inadequate gas exchange may require postoperative ventilation for several days. With large defects, it may be necessary to house the abdominal contents in a prosthesis to allow gradual reduction into the abdominal cavity.

DIAPHRAGMATIC PALSY

Phrenic nerve palsy is a relatively common complication of cardiothoracic surgery. It occasionally occurs as a congenital abnormality, or may result from birth trauma. Paralysis and paradoxical movement of the affected diaphragm lead to reduced lung and tidal volumes, hypoxaemia and increased work of breathing. A chest X-ray taken without positive airway pressure reveals the elevated hemidiaphragm (positive pressure may mask the radiological diagnosis). Screening with ultrasound or fluoroscopy confirms the paradoxical movement.

Paralysis of the hemidiaphragm may cause respiratory failure in infants, particularly if associated with another disorder affecting lung function. Problems are greatest in children under 3 years, due to the poor stability of the chest wall. CPAP may be an effective method of increasing lung volume, stabilising the rib cage and reducing paradoxical movement. Surgical plication of the diaphragm is usually effective in cases that fail to resolve with conservative management.

BIRTH ASPHYXIA

Birth asphyxia may result from placental failure, obstetric difficulties or maternal sedation. The resulting central respiratory depression, convulsions, intracerebral haemorrhage, meconium aspiration and transitional circulation contribute to respiratory failure. The Apgar score at 1 minute is an objective means of evaluating the degree of asphyxia; the score at 5 minutes is a guide to prognosis. Delayed spontaneous respiration (> 5 minutes) is also a poor prognostic sign. Further postnatal hypoxaemia, hypercapnia and brain ischaemia must be avoided. Severely asphyxiated infants need CMV after delivery, with correction of acidosis and hypovolaemia; inotropic drugs may be needed to maintain cerebral blood flow. It is important to prevent hypoglycaemia and control convulsions. A recent randomised control trial has shown improved cerebral outcomes with the use of early topical hypothermia, although the benefit is probably restricted to infants with less severe degrees of hypoxic–ischaemic encephalopathy.¹⁰

CONVULSIONS

Convulsions in the newborn are most frequent in the first 3 days of life. They are commonly due to birth asphyxia, trauma, intracranial haemorrhage and metabolic abnormalities such as hypoglycaemia or hypocalcaemia and meningitis. Seizures in older children commonly occur with fever, idiopathic epilepsy, CNS infection, poisoning, trauma and metabolic disturbances (e.g. hypoglycaemia, hyponatraemia and hypocalcaemia).

Generalised seizures may cause respiratory failure from airway obstruction, aspiration, apnoea or central respiratory depression. During grand mal seizures, ventilation may be inadequate, and oxygen consumption and CO₂ production may be increased by associated muscle activity. Anticonvulsant drugs may further depress respiration.

Initial management consists of ensuring a clear airway, adequate oxygenation and ventilation, and administering anticonvulsants. Oxygen should be given, because cerebral and total body oxygen consumption is increased, and it is difficult to assess adequacy of ventilation. Urgent control of seizures is important, as protracted seizures (longer than 1 hour) cause cerebral oedema and may result in permanent neurological sequelae, even if hypoxaemia is avoided. The underlying cause must then be determined and treated.

APNOEA OF PREMATURITY

Recurrent apnoeic episodes (> 20 seconds) are common in premature infants, and relate to immaturity of the brainstem, hypoxia, altered chemoreceptor responsiveness, diaphragmatic fatigue and the active (rapid eye movement) sleep state. Underlying causes such as hyaline membrane disease, hypoglycaemia, aspiration, sepsis, anaemia and intracranial haemorrhage should be sought. Mild episodes revert either spontaneously or with tactile stimulation. Severe episodes may require bag-and-mask ventilation. Apnoeic episodes may be reduced or prevented by theophylline or caffeine (central respiratory stimulants) or CPAP. IMV is necessary in some cases.

Many premature infants also suffer obstructive or mixed (central and obstructive) apnoea, both disorders of respiratory and airway musculature control. The infant airway collapses easily, and this is aggravated by neck flexion. Ex-premature infants may develop recurrent apnoea with intercurrent infection or following general anaesthesia and surgical procedures. This risk may persist until a postconceptual age of 46 weeks, and demands close monitoring.¹¹ The risk may be greater in infants with a history of apnoeic episodes, bronchopulmonary dysplasia, anaemia or neurological disease. This is transient and remarkably responsive to theophylline or caffeine loading. Ongoing maintenance therapy is often unnecessary.

STATUS ASTHMATICUS

Asthma is the commonest reason for admission to most paediatric hospitals. Asthma is an inflammatory disease affecting the airways. Airway obstruction is due to mucosal oedema, mucus plugging and bronchiolar muscle spasm. Under 2 years of age, bronchiolar muscle is poorly developed, and muscle spasm is probably of less importance, with poor response to bronchodilator therapy.

Clinical and radiological features and management of asthma in small children are similar to that in adults (see Chapter 35). Blood gas estimation is indicated for any child with acute severe asthma, if pulsus paradoxus greater than 20 mmHg (2.6 kPa) is present, or if the child fails to respond to optimal drug therapy. Hypoxaemia due to intrapulmonary shunt and mismatching is the usual finding, and is the main cause of morbidity and mortality. High inspired oxygen therapy is therefore important. Hypocapnia in response to hypoxic drive is the rule; normocapnia or a rising PaCO₂ are signs of worsening asthma or fatigue and require increased medical therapy or mechanical ventilation.

Nebulised and/or i.v. β₂-sympathomimetic amines, i.v. aminophylline and corticosteroids form the mainstay of drug therapy; maximal therapy should be introduced early. Salbutamol is nebulised with oxygen as 0.05 mg/kg of 0.5% solution diluted to 4 ml with sterile water, given 2–4-hourly initially, or more frequently in severe cases. A greater and more sustained response may be achieved by more frequent or continuous salbutamol nebulisation.¹² Inhaled ipratropium may have additional benefit, even in patients receiving maximal therapy with β₂-sympathomimetic amines.

Some centres abandoned the use of aminophylline because of its narrow therapeutic range and because of the belief that it did not add benefit to maximal therapy with salbutamol. There is evidence, however, that aminophylline does have a place in the management of severe acute asthma in children that is unresponsive to initial treatment.¹³ Aminophylline is also known to possess anti-inflammatory properties. A loading dose of 5–10 mg/kg aminophylline over 1 hour produces serum levels in the therapeutic range; lower loading doses may be employed to reduce the occurrence of nausea and vomiting. Children under 9 years have increased metabolism, and require higher doses of theophylline (0.85 mg/kg per hour, equivalent to an aminophylline infusion of 1.1 mg/kg per hour). Serum concentrations should be measured (therapeutic range is 60–110 μmol/l).

Continuous infusion of salbutamol has been shown to reduce the need for CMV. It should be added when PaCO₂ is rising or is greater than 60 mmHg (8 kPa), as an infusion of 5–10 μg/kg per min for 1 hour and then reduced to 1–2 μg/kg per min. An adrenaline (epinephrine) or isoprenaline infusion (0.05–2 μg/kg per min) may be useful in refractory cases.

Lactic acidosis may occur as a result of hypoxaemia and increased work of breathing. Adrenaline by infusion is also associated with lactic acidosis. Cautious bicarbonate therapy is recommended to improve cardiovascular function and bronchomotor responsiveness to theophylline and sympathomimetic agents. Isoprenaline and theophylline may both override pulmonary hypoxic vasoconstrictor responses and thereby increase intrapulmonary shunt and worsen hypoxaemia. Salbutamol is believed to be preferable in this respect.

Particular attention should be paid to fluid balance. Dehydration may lead to inspissation of secretions, but the risks of inappropriate antidiuretic hormone (ADH) secretion and pulmonary oedema must be noted.^14,15

With aggressive medical therapy, the need for CMV should be rare. Its use should be based predominantly on clinical features rather than solely on blood gas analysis. It should not, however, be withheld out of fear of difficulties. CMV may worsen air trapping and lead to hypotension or pneumothorax. Controlled hypoventilation (permissive hypercapnia) with a long expiratory time is advocated to minimise airway pressures and air trapping. A trial of positive end-expiratory pressure (PEEP) may be justified to reduce intrinsic (auto) PEEP and air trapping, although evidence in adults suggests that PEEP may be associated with increased air trapping.¹⁶

ACUTE VIRAL BRONCHIOLITIS

Most cases of bronchiolitis occur in the first 6 months of life and are caused by RSV. Other viruses now identified as causing bronchiolitis include rhinovirus and human metapneumovirus. Cough, low-grade fever, tachypnoea and wheeze are the cardinal signs. Some infants, particularly ex-premature, develop apnoeic episodes. The chest is hyperinflated with rib retraction and widespread crepitations. Clinical features are due to small airways obstruction from oedema and exudate.

Management consists of minimal handling and oxygen therapy. If respiratory distress is marked, feeds should be withheld and fluids administered i.v. Progression of the disease leads to exhaustion and respiratory failure in 1–2% of cases. CPAP and/or aminophylline therapies are reported to reduce the work of breathing, lower PaCO₂ and eliminate recurrent apnoea. Nebulised adrenaline may also be beneficial.¹⁷ CMV is required in some cases, particularly when the disease occurs in association with congenital heart or chronic lung disease. High airway pressures may be required, increasing the risk of pneumothorax. The antiviral agent ribavirin is difficult to administer and has not been shown to improve outcome. Bacterial coinfection is common, and justifies the use of broad-spectrum antibiotics in severe cases.¹⁸

RESPIRATORY FAILURE SECONDARY TO CONGENITAL HEART DISEASE

Infants with congenital heart disease may develop respiratory failure for a number of reasons.

NEAR DROWNING

Respiratory failure after near drowning may result from aspiration pneumonitis or CNS depression from hypoxic–ischaemic encephalopathy. Acute gastric dilatation (associated with the immersion or resuscitation) is common and may be a contributing factor. Pulmonary oedema may be secondary to water and particulate matter inhaled, or to chemical pneumonitis from aspiration of gastric contents. Secondary infection occasionally leads to necrotising pneumonia. Prophylactic antibiotics are not of proven benefit, but there are occasional reports of fulminant ARDS associated with infection after immersion. Broad spectrum antibiotic therapy should be administered early if there is significant pulmonary disease. Ongoing therapy should be guided by culture of tracheal aspirate.

Patients with both fresh- and salt-water drowning are usually hypovolaemic, hypoxic and acidotic at the time of admission. Oxygen therapy is mandatory, even in so-called ‘dry drowning’. Resuscitation usually requires volume expansion, correction of acidosis and inotropic support. Immersion hypothermia may afford some protection to the brain. Complete rewarming should not be undertaken until circulatory resuscitation is achieved. Resuscitation attempts should be sustained in the presence of severe hypothermia; in warmer climates, however, severe hypothermia implies a longer period of immersion and carries a very poor prognosis. In such circumstances it may be appropriate to cease resuscitative efforts prior to rewarming. CMV usually produces a dramatic improvement in gas exchange.

TRAUMA

Respiratory failure may follow trauma to the brain, spinal cord, chest or abdomen. High spinal cord injuries may be difficult to detect in the presence of severe brain injury. Presence of rhythmic flaring of the alae nasi without accompanying respiratory excursion is a useful sign (Duncan’s sign). As the chest wall is compliant, severe pulmonary contusion can occur from blunt trauma with minimal chest-wall injury. Fractured ribs, haemothorax and pneumothorax may all precipitate respiratory failure. The diagnosis of a ruptured diaphragm is often delayed as the clinical signs are easily confused with a tension pneumothorax. CMV will effectively displace abdominal contents from the thorax and improve gas exchange prior to surgery. The chest X-ray is a mandatory investigation during resuscitation.

Acute gastric dilatation is almost invariable in the traumatised child, may mimic an acute abdomen and may exacerbate respiratory failure. Emergency decompression with a wide-bore gastric tube improves cardiorespiratory function and reduces the risk of aspiration.

ACUTE RESPIRATORY DISTRESS SYNDROME

Acute respiratory distress syndrome (ARDS) may occur in children of all ages from a variety of direct and indirect lung insults. ARDS is characterised by respiratory distress or failure, diffuse pulmonary infiltrates, reduced pulmonary compliance and hypoxaemia in the presence of a known precipitating cause and in the absence of left ventricular failure. In children, common causes include shock from any cause, pneumonia, sepsis, near drowning, aspiration and pulmonary contusion.

POISONING

Accidental poisoning is a common but preventable cause of respiratory failure, particularly in the first 4 years of life. Deliberate overdose is seen in children beyond 8 years. Tricyclic antidepressants, antihistamines, anticonvulsants and attention deficit hyperactivity disorder (ADHD) medications (clonidine, methylphenidate, dexamfetamine) are now the commonest CNS-affecting drugs ingested. Convulsions may aggravate the situation.

MENINGITIS AND ENCEPHALITIS

Meningitis is common in the early years of life. After the neonatal period, the usual causative organisms are Haemophilus influenzae, Neisseria meningitidis and Streptococcus pneumoniae. Immunisation has markedly reduced the incidence in developed countries. Rapid diagnosis and appropriate antibiotic therapy form the cornerstone of treatment. Respiratory failure is mainly associated with uncontrolled convulsions, altered conscious state or raised intracranial pressure (ICP).

Encephalitis may also cause unconsciousness and raised ICP. Associated problems are upper airway obstruction, pulmonary aspiration and central respiratory depression. In many cases of encephalitis, a causative organism is not found although viral or postinfective causes are suspected. The antiviral agent, aciclovir, should be administered until herpes encephalitis is excluded. Hyperpyrexia, convulsions and cerebral oedema may complicate encephalitis.

GUILLAIN–BARRÉ SYNDROME

This is the most common polyneuritis in childhood. Ascending paralysis may involve the intercostal muscles, the diaphragm and bulbar muscles. The onset may be rapid, with respiratory failure occurring within 48 hours. Intervention is based on clinical assessment of cough reflex and bulbar function, a measured vital capacity < 15 ml/kg, and evidence of hypoxaemia (SaO₂ < 90%). Hypoxaemia occurs relatively early due to reduced functional residual capacity, atelectasis and intrapulmonary shunting. An elevated PaCO₂ is a late feature, suggesting a vital capacity in the tidal range, i.e. < 5–7 ml/kg. CMV is usually necessary if intubation is required. Unless rapid recovery is anticipated, early tracheostomy is advocated for patient comfort, to allow speech and to facilitate mobilisation. The condition is often improved by the early use of i.v. immunoglobulin therapy or plasmapheresis. Immunoglobulin is easier to deliver and probably safer. Other complications relate to autonomic involvement (arrhythmias, blood pressure lability) and ileus. Muscle pain may require analgesic relief.

Transverse myelitis may present in a similar manner and the principles of management are the same. Nerve conduction studies and MRI may be necessary to distinguish between the two conditions. Immunoglobulin therapy and plasmapheresis, however, are not effective. There are some reports of benefit from steroid therapy.

ENVENOMATION

Some animal venoms, such as those of some snakes, ticks and blue-ringed octopus, are neurotoxic and may cause muscle weakness and respiratory insufficiency. The Sydney funnel-web spider causes widespread acetylcholine release and symptoms similar to anticholinesterase poisoning. These symptoms include intense salivation, lacrimation, sweating, laryngeal and muscle spasm and pulmonary oedema. Paralysis due to tetrodotoxin may rapidly follow puffer-fish ingestion. In Australia and many other countries, specific antivenom therapy is available for most potentially lethal envenomations. Supportive therapy is required until antivenom is administered and recovery occurs.

MANAGEMENT OF ACUTE RESPIRATORY FAILURE

In some cases, definitive treatment of the underlying cause will lead to resolution of respiratory failure (e.g. relief of upper airway obstruction or reversal of drug depression). Where this is not possible, mechanical ventilatory support is required until the underlying process has resolved.

GENERAL MEASURES

SPECIFIC MEASURES