In a fetus, there is high pulmonary vascular resistance and low pulmonary blood flow as the fetus does not use the lungs for oxygen transfer. Once the baby is born, the lungs are needed for oxygen transfer and need high blood flow which is encouraged by low pulmonary vascular resistance.
It can be associated with pulmonary hypertension. Because of this, the condition is also known as "persistent pulmonary hypertension of the newborn".
Treatment aims to increase the amount of oxygen in the blood and reverse any causes of hypoxia.
The therapies available to manage PPHN include the high frequency ventilation, surfactant instillation, inhaled nitric oxide, and extracorporeal membrane oxygenation. These expensive and/or invasive modalities are unavailable in the developing countries where the frequency and mortality of PPHN is likely to be much higher due to higher incidence of asphyxia and sepsis. In developing countries, the medical facilities are usually supplied with outdated equipment that was initially donated. "For people in developing countries, basic medical supplies are luxuries that are simply not available or not affordable. Doctors and nurses must constantly make do - washing and reusing "disposable" gloves and syringes, or substituting inappropriate materials such as fishing line or sewing thread for suture- or patients must go without needed care. In many countries patients must bring their own supplies, even acquire their own medicines, before treatment can be given." The limitations made it necessary to search for cheaper therapies, assuring quick effectiveness and stabilization of the patient going through a very high-risk situation. The treatments are chosen on the basis of low cost, low-tech, wide availability, and safety in the hands of non-professionals. Therefore, oral sildenafil citrate, has been the alternative way of therapy. The cost comparison shows that sildenafil is lower in cost than iNO and more readily available. There is improvement in oxygenation when oral sildenifal is administered according to the studies found in the Official Journal of the American Academy of Pediatric. The positive research results for varies studies indicates that oral sildenifal is a feasible source to improve oxygenation and survival in critical ill infants with PPHN secondary to parenchymal lung disease in centers without access to high-frequency ventilation, iNO, or ECMO.
^Chambers CD, Hernandez-Diaz S, Van Marter LJ, et al. (February 2006). "Selective serotonin-reuptake inhibitors and risk of persistent pulmonary hypertension of the newborn". The New England Journal of Medicine354 (6): 579–87. doi:10.1056/NEJMoa052744. PMID16467545.