The infant with breathing difficulty

Respiratory emergencies are some of the commonest conditions presenting in the neonatal period. The increased work of breathing is manifested as:

The causes of respiratory distress are varied and are summarised in Table 26.1.1. They can be broadly divided into primary respiratory and non-respiratory causes. Primary respiratory pathology is a direct result of upper, lower or mixed airway pathology.

This section will discuss:

Upper airway obstruction

Respiratory distress attributed to lung parenchyma pathology

Clinical features

History

In respiratory distress attributed to parenchymal involvement, a clinical history is essential to elucidate potential predisposing factors. Of the causes of parenchymal disease presenting to the ED, pneumonia and extra-pulmonary cardiac failure are the two most common causes. These can often be differentiated by clinical history.

Bacterial pneumonia in the first few hours of life may be impossible to distinguish from respiratory distress syndrome or transient tachypnoea of the newborn. Therefore, respiratory distress in newborns generally should be treated as bacterial pneumonia until proven otherwise. When associated with chorioamnionitis, it is caused most commonly by Group B streptococci (GBS) or by Escherichia coli. However, Haemophilus influenzae, Streptococcus pneumoniae (pneumococcus), Group D streptococci, Listeria and anaerobes have also been described as pathogens in this setting. Infants infected with these organisms are often preterm and have very early onset of respiratory distress. Of note, infants may also develop bacterial pneumonia transnatally in the absence of maternal chorioamnionitis. Here, the causative organism is likely to be GBS, and the onset of symptoms tends to occur 12–24 hours after birth.

Neonatal pneumonia can be either congenital or acquired. Congenital pneumonia commences before birth and the most common infecting organisms include Group B Streptococcus and E. coli. Despite the majority of infants being unwell at birth, some infants do acquire these infections after birth and present with similar signs and symptoms of respiratory distress, poor feeding, fever and apnoea. The clinical history should focus on the maternal Group B Streptococcus carriage in pregnancy, length of rupture of membranes, maternal antibiotic therapy during labour and maternal fever. Acquired neonatal pneumonias are commonly viral, with respiratory syncytial virus, adenovirus and parainfluenza virus all commonly identified. A history of affected family members gives some indication of this potential.

Any infant with underlying lung pathology is at risk of air leak, and any sudden decompensation in an infant with respiratory distress should lead one to consider this diagnosis. In addition, air leak can be a spontaneous phenomenon with no identified cause.

Non-infectious causes of acquired respiratory distress include any conditions in which there is an abnormally high or low blood flow to the lungs, an increased demand for oxygen, or a decreased number of red blood cells.

The commonest non-pulmonary cause of respiratory distress seen in the ED is that of pulmonary oedema, secondary to congenital heart disease.

Congenital heart disease is one of the commonest malformations, with an incidence of 0.6%. Although 30–60% of congenital heart disease is identified antenatally, this still leaves a large percentage presenting in the postnatal period. Predischarge saturation monitoring of all newborn infants has the possibility of increasing the early identification of congenital heart disease, prior to the onset of respiratory distress, cyanosis or collapse. Cyanotic lesions generally present early but neonates with ductal-dependent systemic circulations are often well in the early neonatal period and collapse around day 4 of life. Closure of the ductus, with associated systemic collapse, is one of the commonest presentations to the ED with severe respiratory distress, secondary to associated pulmonary oedema.

Factors in the history pointing towards congenital heart disease being the cause of collapse include a family history, syndromic malformations and associated abnormalities.

In addition to predisposing factors, a history of poor feeding often predates the collapse.

Other causes of respiratory distress presenting in the ED are:

• inborn errors of metabolism, with associated acidosis, a family history, consanguinity or an abnormal smell noted from the infant;

• central nervous system anomalies;

• non-accidental injury.

Examination

Infants with disease affecting the lung parenchyma, either primary respiratory or cardiac, generally present with the classical examination findings of respiratory distress, notably: recession of the intercostal and subcostal spaces; nasal flaring; tachypnoea (>60 bpm); and expiratory grunting.

Nasal flaring is a result of the alae nasi being the first muscles to be activated during inspiration and they aim to decrease airway resistance. The recession of the inter- and subcostal spaces is a result of the compliance of the chest wall being reduced in neonates. During inspiration the pleural pressure is reduced, but in neonates with parenchymal lung disease this needs to be reduced more than normal and thus the consequences are that the compliant chest wall may cave in as a result of these more negative pressures. The recession in conjunction with the abdominal protuberance associated with diaphragmatic descent give the characteristic seesaw pattern of neonatal respiratory distress.

Infants with respiratory infections may present in a very similar manner to those with cardiac anomalies. Specific findings for infants with pneumonia may be the presence of fever or temperature instability, feed intolerance and rhinorrhoea.

If there is a suggestion of pulmonary air leak, the clinical signs are specific. There will be reduced air entry on the side of the leak, with a reduction in chest movement on that side. Percussion, although seldom used in newborn infants, should be hyper-resonant and if the air leak is under tension there may be associated displacement of the trachea and apex beat to the contralateral side.

If a primary respiratory cause cannot be identified, non-respiratory causes should be sought. Signs indicative of congenital heart disease may include weak femoral pulses, an active praecordial impulse, hepatomegaly and a cardiac murmur.

The classic cardiac lesions presenting with respiratory distress in the neonatal period include:

Left to right shunting lesions (atrioventriculoseptal defects (AVSD) and ventriculoseptal defects (VSD)). Typically, large VSDs present between weeks 2 and 4 of life after the pulmonary pressures have reduced and this allows increased left to right flow with resultant pulmonary oedema. The infant will present with increasing tachypnoea, recession and poor feeding, in association with a loud cardiac murmur and crepitations audible in the chest.

Duct-dependent obstructive left ventricle conditions (hypoplastic left heart, critical aortic stenosis and coarctation of the aorta). Once the ductus arteriosus closes around week 1 of life, the systemic circulation is no longer maintained. Infants present shocked, pale and with severe respiratory distress. Specifically they have weak femoral pulses and invariably a large liver.

With other causes of respiratory distress there may be features consistent with specific diagnoses. Metabolic conditions are often associated with hepatosplenomegaly, coma, hypoglycaemia and jaundice. Central nervous system (CNS) lesions may have seizures associated.

Investigations

Any infant in the first month of life with respiratory distress should be observed and monitored closely. This includes pulse rate, oxygen saturation, respiratory rate, temperature, blood pressure and capillary refill time.

The normal heart rate for a neonate in the first month of life is 120–160 bpm. Some newborn infants, however, have a resting heart rate below 90 bpm. Respiratory distress is generally associated with respiratory rate greater than 60 breaths per minute. Fever as a sign of sepsis is variable.

Plain radiographs of the chest are useful, but do not generally differentiate the various causes of respiratory distress. Sepsis and cardiac failure both demonstrate increased interstitial markings. In cardiac failure, fluid more specifically radiates into the interstitium from the hilum and in severe cases may be associated with an effusion. Again, in cardiac disease the size of the cardiac shadow may be increased. A cardiac silhouette greater than 60% of the transthoracic diameter is indicative of cardiac disease and needs to be investigated further, by means of an electrocardiogram and echocardiogram, and referral to a cardiologist.

The chest radiograph of an infant with pneumonia may show lobar or diffuse interstitial changes. Chest radiographs of infants who have bacterial pneumonia may exhibit a diffuse reticular nodular appearance but, in contrast to respiratory distress syndrome, they tend to show normal or increased lung volumes with possible focal or coarse densities. There may also be pleural effusions, particularly with GBS pneumonia. In the newborn who has bacterial pneumonia, blood cultures obtained before the initiation of antibiotics commonly grow the offending organism. Cultures of urine and cerebrospinal fluid should be obtained at the time of the blood culture if a newborn infant is systemically unwell. If the diagnosis is viral, mucus plugging, with over-aeration and hyper-expansion may be characteristic. Although tension pneumothorax should be a clinical diagnosis, the plain radiograph is good at demonstrating small pneumothoraces. An anterior pneumothorax may be subtle and easily missed by the unwary as appearing more lucent on the side of the pneumothorax in the absence of a lateral air meniscus.

Laboratory investigations, including full blood count, C-reactive protein (CRP) and blood cultures, are useful adjuncts to the diagnosis. The white cell count may show a leucocytosis with associated left shift or, more commonly, may show a consumptive picture with neutropenia and associated thrombocytopenia in the septic infant. The CRP is another non-specific marker of infection, but appears more useful in monitoring response to treatment of infection rather than in its diagnosis.

If a viral respiratory tract infection is suspected then a nasopharyngeal sample viewed with electron microscopy for respiratory viruses may reveal the common causes of bronchiolitis.

Arterial blood gas analysis or indirect transcutaneous monitoring may reveal arterial hypoxaemia and hypercarbia. The degree of hypoxaemia and acidosis will be a guide to the need for respiratory positive pressure support. In addition to diagnosing the severity of the respiratory acidosis, an arterial blood gas may also reveal a metabolic acidosis, making inborn errors of metabolism a potential differential diagnosis of the respiratory distress.

Management

A neonate with respiratory distress needs to be observed closely. Evaluation of airway, breathing and circulation are imperative, as outlined in the resuscitation guidelines devised by the International Liaison Committee on Resuscitation (ILCOR). Maintaining a neutral airway position and ensuring the airway is free of obstruction allows optimal oxygen to be delivered. Saturations should be maintained with either nasal cannulae oxygen, head box oxygen, continuous positive airways pressure or endotracheal intubation and ventilation. If working in a hospital with a Neonatal Intensive Care Unit or Paediatric Intensive Care Unit, support from personnel working in these areas can be invaluable in maintaining a patent airway.

If sepsis is suspected then intravenous antibiotics should be commenced, to cover both Gram-positive and Gram-negative bacteria and an evaluation made of the need for both fluid and inotropic support. Empiric treatment should be initiated as soon as possible with ampicillin 100 mg kg^–1 day^–1 divided every 12 hours (infants <1.2 kg) or every 8 hours (infants >1.2 kg) and cefotaxime 100 mg kg^–1 day^–1 divided every 12 hours or 150 mg kg^–1 day^–1 divided every 8 hours (infants >1.2 kg and >7 days old). Gentamicin is an alternative treatment, particularly when there is no evidence of meningitis. Treatment should be continued for at least 10 days if sepsis is present, although 14–21 days may be required, particularly for Gram-negative infections.

Viral infections are treated conservatively by respiratory and circulatory support as required. An unusual or unresponsive neonatal presentation of pneumonia warrants further evaluation. The maternal history may offer important clues. Neonatal pneumonia involving cytomegalovirus (CMV) or other viruses may be transmitted transplacentally. CMV pneumonia may not require treatment in the otherwise healthy infant. However, neonatal respiratory distress in the setting of perinatal exposure to herpes simplex virus, particularly if there is primary maternal genital infection, warrants treatment with aciclovir 30 mg kg^–1 day^–1 divided every 8 hours for 14–21 days until all cultures are negative. Ureaplasma urealyticum is another important organism and treatment of Ureaplasma infections in the newborn should include erythromycin 50 mg kg^–1 day^–1 divided every 6 hours.

If the cause of the respiratory distress is believed to be cardiac then once again supporting the airway, breathing and circulation is imperative. Added caution with fluid resuscitation should be considered so as not to exacerbate the cardiac failure. Use of prostaglandin E1 allows reopening of the ductus and increased systemic circulation. This is a temporising measure prior to the definitive surgery the infant may require.

Management of a pneumothorax requires either acute drainage with needle thoracocentesis, in the presence of a tension pneumothorax, or intercostal catheter insertion followed by appropriate underwater drainage. A repeat chest X-ray (CXR) to ensure adequate lung expansion is required prior to the removal of the chest drain.

The blue infant

Neonatal cyanosis is a result of deoxygenated blood in the systemic circulation. It is defined as an arterial saturation less than 90%.

History, examination and simple investigations available in the ED should be able to distinguish the cause of the cyanosis and this will predict the management of this condition.

Causes

Babies can be peripherally blue or centrally blue and this is important in differentiating the cause of the cyanosis. Peripheral cyanosis, affecting the hands and feet, known as acrocyanosis is a normal phenomenon that generally clears within 1–2 days and needs no treatment. Central cyanosis, evidenced by cyanosis of the gums and mucous membranes is generally pathological and needs urgent evaluation if presenting in the ED. Babies can be centrally cyanosed for many reasons including heart disease, lung or other breathing problems, being cold, or having seizures. Not all children who turn blue have a heart problem. A thorough history, examination and simple investigations will be able to differentiate these causes of central cyanosis.

Non-respiratory causes of cyanosis

• Cardiac defects:

Decreased pulmonary blood flow

Admixture lesions

Congestive heart failure (pulmonary congestion).

• Primary pulmonary hypertension of the newborn.

• Central nervous system disease:

Intracranial haemorrhage

Maternal sedative administration

Meningitis.

• Methaemoglobinaemia.

• Hypoglycaemia.

• Sepsis.

• Cold.

Clinical features

History

Once cyanosis has been diagnosed in an infant presenting to the ED, the most important step is to differentiate between pulmonary and cardiac causes of cyanosis.

Pulmonary causes of cyanosis include pneumonia, both bacterial and viral, pneumothorax, pleural effusions and airway anomalies. If the cause of the cyanosis is felt to be pulmonary, the infant will generally have a history of worsening respiratory distress that interferes with the infant’s ability to feed successfully. The history may be indicative of an infective cause, with rhinorrhoea, fever, cough, poor feeding and worsening recession of the inter- and subcostal spaces. In addition, there may be a history of other affected family members and respiratory infections are generally more prominent in the winter months especially associated with epidemics of bronchiolitis.

Infants with cardiac causes of cyanosis may have no preceding history and generally breathe normally. A detailed antenatal history, including family history, genetic abnormalities and the results of antenatal ultrasound scans, will be important. In addition, the timing of the cyanosis may also give a clue to the diagnosis, with duct-dependent cardiac lesions generally worsening when the ductus arteriosus shuts around day 3 or 4 of life. Although congenital heart disease is generally divided into cyanotic and acyanotic, those lesions generally classified as acyanotic but duct dependent can present with severe respiratory distress and a degree of cyanosis.

In addition to congenital heart disease and pulmonary causes, an infant may present cyanosed because they have neurological depression or seizures. A history of the infant’s general activity, tone and feeding patterns will be helpful. Infants with neurological depression may be hypotonic, have abnormal autonomic responses and have poor feeding with associated failure to thrive and may indeed have seizure activity.

Once again, if seizures are suspected then a detailed family history may indicate a genetic syndrome as the cause of the seizures. A thorough history of the pregnancy and delivery is also important to rule out other causes of seizures, and early checking for hypoglycaemia is essential. Considering neonatal sepsis is always imperative and a detailed history of maternal substance abuse may indicate drug withdrawal as the cause of the seizures.

Examination

Once a detailed history has been taken to elicit possible causes of cyanosis then the infant should be examined carefully.

Infants with respiratory causes for cyanosis will generally have signs of distress, namely tachypnoea, recession of the intercostal and subcostal spaces, tracheal tug, nasal flaring and expiratory grunting. As to the precise respiratory cause of this distress, septic infants often have an associated tachycardia and may have temperature instability. They may have poor capillary return and may also have associated apnoeas, a pause in breathing of greater than 20 seconds or a pause in breathing less than 20 seconds but associated with bradycardia. Infants who are septic and cyanosed may have localised respiratory infections, such as viral bronchiolitis, or may be septicaemic.

A cyanosed infant with little or no respiratory distress is more likely to have congenital heart disease. The commonest lesions presenting with cyanosis in the neonatal period are: transposition of the great arteries; total anomalous pulmonary venous return; pulmonary atresia with an intact ventricular septum; severe pulmonary stenosis; and severe tetralogy of Fallot.

Examination of a cyanosed infant with suspected cardiac disease might reveal dysmorphic features suggesting a syndromic association with congenital heart disease. Auscultation of the lung fields and praecordium may reveal evidence of pulmonary oedema and murmurs, and an abdominal examination may reveal hepatomegaly.

To differentiate an infant with non-cardiopulmonary causes for the cyanosis, the examination would need to concentrate on the neurological system of the infant. Tone, movements and reflexes will all give important information as to the neurological status. Examination for dysmorphic features and examination of the fundi and skin may add important information as to the cause of the seizures. In the neonatal period, important causes of seizures would include hypoxia, hypoglycaemia and biochemical anomalies, narcotic withdrawal and structural brain abnormalities.

Investigations

To differentiate the various causes of cyanosis in the neonatal period a full set of observations should be performed. Oxygen saturations should be performed initially in room air to serve as a baseline. Subsequent oxygen measures should be performed in 100% oxygen, achieved by means of a headbox sealed over the baby’s head and neck. The so-called hyperoxia test may help to differentiate cyanotic heart disease from other causes of neonatal cyanosis. Infants with neurological or pulmonary causes of the cyanosis will demonstrate substantial increases in the arterial blood saturation, while infants with cyanotic congenital heart disease will show minimal elevation. As well as oxygen saturation changes, the difference should be confirmed with arterial blood gas analysis of arterial oxygen partial pressures. A partial pressure <100 mmHg in 100% inspired oxygen is more indicative of cardiac disease.

Once arterial oxygen saturations and blood gas analysis have been performed the infant should have a chest radiograph. Abnormalities of the lung fields may suggest a primary pulmonary cause for the cyanosis or a cardiac cause if the changes are suggestive of pulmonary oedema with increased vascular markings.

Assessing the cardiothoracic diameter and shape of the cardiac shadow may give some clues to a cardiac cause of the cyanosis. A typical boot-shaped heart is classically described in tetralogy of Fallot and an egg on a string appearance is described in transposition of the great arteries. Generally differentiating the cardiac causes of cyanosis is difficult and requires an echocardiogram. Additional investigations that may be useful in the diagnosis of neonatal cyanosis include a full blood count to reveal polycythaemia and a raised or depressed white blood cell count, blood cultures and a nasopharyngeal aspirate.

In addition to blood gas analysis to indicate fixed or variable hypoxia, the carbon dioxide will generally be raised in respiratory pathologies contributing to the cyanosis but may be normal in cardiac disease.

An electrocardiogram (ECG) may help differentiate cardiac disease, but the gold standard investigation to help differentiate cardiac causes of cyanosis from non-cardiac causes will be an echocardiogram combined with colour Doppler flow mapping and pulsed-wave Doppler studies. The echocardiogram should be performed as a matter of urgency in such situations to allow appropriate management of congenital heart disease. Echocardiography can be easily performed by a paediatric cardiologist in the ED or the infant may need to be transferred to a specialist centre to achieve such an investigation.

If a neurological cause is suspected for the cyanosis, urgent investigation including blood sugar level monitoring is imperative. Additional biochemical investigations may include calcium, magnesium and sodium as well as specific metabolic investigations, including a urine metabolic screen and newborn screening test if inborn errors of metabolism are suspected to be causing neurological depression. If structural lesions or intra-cerebral haemorrhage is suspected, ultrasound is an easy bedside test to perform, but magnetic resonance imaging is the gold standard for CNS investigation. Additional investigations may include electroencephalogram (EEG) and urine/meconium drug screening.

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