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Pulmonary hypertension of the newborn with right to left shunt occurs in a variety of clinical situations. These include Meconium Aspiration Syndrome, hypoplastic lungs, transient tachypnoea of the newborn, congenital pneumonia and hyaline membrane disease. Secondary disturbances such as polycythaemia and myocardial failure are contributory. There is frequently a history of chronic in utero hypoxia, but some cases remain idiopathic.
- Pulmonary vasoconstriction is exacerbated by hypoxia, acidosis, and hypercapnia (secondary to changes in pH). Meconium may trigger vasoactive process to exacerbate this.
- Anatomic abnormality of the pulmonary vascular bed (e.g. pulmonary hypoplasia with pulmonary arteriolar smooth muscle hypertrophy) or chronic in-utero hypotension following chronic intrauterine hypoxia may also play a role.
- Birth asphyxia with hypoxia, acidosis and shock is clinically associated with increased responsivity of the pulmonary vascular bed.
- Group B streptococcal sepsis via Strep polysaccharide toxins.
- Polycythaemia, hyaline membrane disease, hypocalcaemia and hypoglycaemia may contribute similarly.
- Structural lung abnormalities (e.g. congenital diaphragmatic hernia, CCAM, ...) are frequently associated with PPHN.
- This is essentially one of exclusion of significant cyanotic congenital heart disease and severe parenchymal lung disease. However, PPHN may coexist with significant parenchymal lung disease.
- Have a high index of suspicion for the 'at risk' group in a term baby with respiratory distress and cyanosis, particularly if there has been a history of intrauterine hypoxia and meconium exposure or birth asphyxia.
Necessary tests may include
- chest xray
- serial arterial blood gases (simultaneous pre- and post-ductal samples may be helpful)
- full blood count
- blood cultures
- blood glucose
This is crucial to exclude cyanotic congenital heart disease (particularly transposition of the great arteries, and totally anomalous pulmonary venous return). In the presence of significant parenchymal lung disease, cardiac assessment is less urgent.
Echocardiography is also useful to
- assess myocardial function, which is often severely affected
- assess the severity of PPHN, and assess responses to treatment.
- Tricuspid regurgitation - allows indirect measurement of the RV pressure and therefore severity
- Ductual shunting
- Shunting through the foramen ovale
- The hyperoxic test may play a role in diagnosis if 2D echocardiography is not available. However, severe PPHN is likely to produce a similar result to cyanotic CHD.
- Lower pulmonary vascular resistance.
- Maintain systemic blood pressure.
- Reverse right-to-left shunting.
- Improve arteriolar oxygen saturation and oxygen delivery to the tissues.
- Minimize barotrauma.
1. Oxygen and ventilation
3. Avoid polycythaemia
6. Muscle Relaxation
7. Pulmonary vasodilators