Respiratory disease in a neonate: Persistent pulmonary hypertension (PPH) Flashcards
Define persistent pulmonary hypertension.
Persistently raised pulmonary vascular resistance which results in shunting of blood away from the lungs via the ducturs areteriosus and foramen ovale
Explain the aetiology of persistent pulmonary hypertension.
May be primary (idiopathic) or secondary to:
- Severe surfactant deficiency
- Meconium aspiration syndrome (MAS)
- Pulmonary hypoplasia (congenital, oligohydramnios)
- Diaphragmatic hernia
- Congenital pneumonia
- HIE
What conditions are associated with persistent pulmonary hypertension?
IUGR
Fetal distress
Down Syndrome
What is the pathophysiology of persistent pulmonary hypertension?
After birth pulmonary vascular resistance normally decline rapidly as a consequence of pulmonary vessel vasodilation secondary to lung inflation, increasing PaO2, decreasing PaCO2 and increasing pH.
Three main mechanisms lead to failure or compromise of pulmonary vessel vasodilation:
- Maladaption of the pulmonary circulation due to injury: This leads to an abnormal response to lung inflation.
- Chronic fetal hypoxia: Causes pulmonary artery constriction via leukotriene activation.
- Obstruction of vasculature: Secondary to polycythaemia
Summarise the epidemiology of persistent pulmonary hypertension.
1/500- 700 live births; occurs in term and preterm infants
What are the signs and symptoms of persistent pulmonary hypertension?
Should be suspected in all infants when hypoxaemia is out of proportion to the severity of parenchymal lung disease on CXR. Hypoxia is universal in all causes of PPH and does not respond to 100% O2 (hyperoxia test).
Signs of respiratory distress: Tachycardia, tachypnoea, recession; intercostal/subscostal/sternal/substernal/ and cyanosis O2.
Signs of cardiogenic shock: May occur secondary to myocardial ischaemia and papillary muscle dysfunction with mitral and tricuspid regurgitation; presents with sings of decrease end-organ perfusion; oliguria, lethargy, hypotension.
What are appropriate investigations for persistent pulmonary hypertension?
Bloods: ABF, Hb, WCC, blood glucose and clotting screen.
CXR: Oligaemic lungs.
ECHO: To exclude CHD and extend of right to left shunt through patent forame ovalue.
What is the antenatal management for persistent pulmonary hypertension?
At-risk infants should be identified in the antenatal period. Correct any predisposing conditions (hypoglucaemia and polycythaemia)
How is dilation of pulmonary vasculature treated?
Ventilation: Lung inflation and oxygen are the two most potent natural pulmonary vasodilatorys. Tight control of pH, PaO2, PaCO2 is required. HFO ventilation may improve gas exchange in these children.
Surfactant: + Additional dose especially in surfactant deficiency and MAS.
Inhaled nitric oxide (NO): A selective pulmonary vasodilator leads to smooth muscle relaxation. Monitor levels of methaemoglobin.
Metabolic acidosis: Correction of acidosis causes pulmonary vasodilation and improves cardiac output as acidosis has a negatively inotropic effect.
Cardiovascular support: Inotropes may be required to optimise cardiac output and BP.
ECMO: A very effective rescue strategy for those who fail other treatments.
What are complications associated with persistent pulmonary hypertension?
Severe hypoxia has deleterious effects on all organs but especially the brain (HIE), gut (NEC) and kidneys (ARF).
What is the prognosis of persistent pulmonary hypertension?
With appropriate treatment, complications are avoided and prognosis is usually the same as that of the underlying pathology.
