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PVR drops from high foetal values during the transition to ventilation of the lungs at birth, resulting in an 8 to 10-fold increase in pulmonary blood flow (Qp). This transition does not occur in all neonates, resulting in Pulmonary Hypertension (PH). In infants, PH can manifest as (a) primary PH in term neonates (idiopathic), (b) PH secondary to lung disease or hypoplasia in term infants, (c) acute PH in preterm infants with Respiratory Distress Syndrome (RDS), (d) chronic PH in preterm infants with Bronchopulmonary Dysplasia (BPD), and (e) post-neonatal PH. Due to elevated Qp, a hemodynamically significant Patent Ductus Arteriosus (PDA) might worsen PH in premature newborns. BPD with PH can be complicated by Pulmonary Vein Stenosis (PVS). Clinical characteristics, echocardiography, and, in some persistent cases, cardiac catheterization are used to diagnose PH. Oxygen, invasive or non-invasive ventilation, acidosis correction, surfactant, and selective and non-selective pulmonary vasodilators such inhaled nitric oxide and sildenafil are all used to treat PH. Early closure of a hemodynamically significant PDA has the potential to reduce BPD and PH-related Pulmonary Vascular Remodelling. With the recent increase in thiamine-responsive acute pulmonary hypertension in early infancy, the function of thiamine in the pathophysiology of PH is also explored. Right ventricular dysfunction, uncoupling, and failure can all be avoided with early detection and treatment of PH.
