Respiratory disease in a neonate: Respiratory distress syndrome

Question 1

Define respiratory distress syndrome.

Answer 1

Respiratory compromise in a premature neonate secondary to surfactant deficiency.

Question 2

Explain the aetiology of respiratory distress syndrome.

Answer 2

Surfactant deficiency leads to high alveolar surface tension, alveolar collapseand intrapleural right-to-left shunting. May be primary surfactant deficiency (prematurity and intrapartum hypoxia, acidosis, hypothermia and hypotension) or secondary (intrapartum asphyxia, pulmonary infections or haemorrhage, meconium aspiration pneumonia). Respiratory compromise also worsened by small lung volumes secondary to immaturity and soft thoracic cage (with attempts to generate a large negative intrathoracic pressure, the ribs and sternum ‘cave in’ and the abdominal contents are displaced downwards – leads to the characteristic ‘see-saw’ breathing).

Question 3

What are risk factors for respiratory distress syndrome?

Answer 3

Prematurity

Maternal diabetes

Caesarean section delivery infants

Second-born twins

FHx

Question 4

What is the pathophysiology of respiratory distress syndrome?

Answer 4

Macroscopic: Lungs appear airless and ruddy (liver-like).

Microscopic: Diffuse atelectasis of the distal airspaces with distention of some of the distal airways and perilymphatic areas.

Question 5

Summarise the epidemiology of respiratory distress syndrome.

Answer 5

50% of infants born at 28-32/40 gestation.

Majority of neonates < 28 weeks, rarely term neonates.

Question 6

What are the signs and symptoms of respiratory distress syndrome?

Answer 6

Progressive signs of respiratory distress: Tachypnoea, expiratory grunting (from partial closure of glottis), subcostal and intercostal retractions, cyanosis, nasal flaring; with extremely premature infants apnoea +/- hypothermia may develop. May progress rapidly to fatigure, apnoea and hypoxia.

Question 7

What are appropriate investigations for respiratory distress syndrome?

Answer 7

Blood gas:

• Respiratory acidosis secondary to alveolar atelectasis +/- overdistension of terminal airways.
• Metabolic acidosis due to lactic acidosis secondary to poor tissue perfusion.
• Hypoxia due to right-to-left shunting

CXR: Bilateral diffuse reticular granular or ground-glass appearance, air bronchograms and poor lung expansion.

Echo: PDA

Question 8

How is respiratory distress syndrome prevented?

Answer 8

Identification of at-risk infants, neonatologist/NICU early involvement.

Amniocentesis for estimation of fetal lung maturity by lecithin:sphingomyelin ratio and presence of phosphatidylglycerol in at-risk infants.

Antenatal steroids stimulate fetal surfactant production (used when preterm delivery is anticipated).

Question 9

How is respiratory distress syndrome treated?

Answer 9

Surfactant replacement therapy via ETT; decreased mortality by 40%, should be given prophylactically at delivery (intubation).

Correction of hypoglycaemia, hypothermia and electrolyte imbalances.

Ventilation: Either continuous positive airway pressure (CPAP) via nasal cannula or conventional mechanical ventilation. High-frequency oscillatory ventilation (HFOV) may have to be used. Regional variation in ventilatory protocols.

Prophylactic antibiotics after blood cultures.

Gentle/minimal handling, enteral or parenteral nutrition.

Question 10

What are complications associated with respiratory distress syndrome?

Answer 10

Acute: Alveolar rupture leading to pneumothorax, intracranial haemorrhage, and periventricular leucomalacia (ischaemic necrosis of periventricular white atter), PDA, pulmonary haemorrhage, NEC or GI perforation.

Chronic: Chronic lung disease of prematurity, retinopathy of prematurity (secondary to oxygen therapy), neurological impairment.

Question 11

What is the prognosis of respiratory distress syndrome?

Answer 11

Previously extremely poor (60% mortality) but improving with antenatal steroids, surfactant therapy and improvements in ventilation. Better prognosis > 1500g.