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Question: What is PPHN (persistent pulmonary hypertension of the newborn)?
PPHN is a condition in which the pulmonary vascular resistance (PVR) does not drop at birth; PVR is the resistance to flow which must be overcome to push blood through the lungs. The prevalence of this condition is estimated at one to two cases per 1,000 live births. It primarily occurs in babies born .34 weeks gestation, although prematurely born infants can also suffer from it. As part of normal fetal development, the PVR is very high to allow blood to preferentially flow to the placenta instead of to the lungs. This occurs because the lungs are not participating in gas exchange so the fetus relies on its motherfs placenta to enrich blood with oxygen. With the first few breaths at birth, the lungs open up, the blood vessels dilate, the PVR begins to drop dramatically and blood flow is now directed to the lungs as the sole source of oxygen. This transition occurs gradually in the course of the first few days to two weeks of life.
However, in certain situations, this decrease in PVR does not occur and PPHN results. PPHN is unique from other types of PH in that this is a developmental or adaptive problem which occurs in the newborn period. The mechanism of PPHN can be understood in two broad types:
This is a condition of hypoplasia, or undergrowth. As a result, there are fewer blood vessels in the lungs, and the PVR is naturally higher to start. There is some ability of the blood vessels to widen after birth, but itfs limited. These infants have PH at birth which does not naturally improve.
Vascular constriction and maladaptation
The lungs and blood vessels are normally developed in these infants, but the blood vessels themselves are constricted or narrowed. Itfs thought that this occurs in response to abnormal levels of hormones in the body. This is typically seen as a reflection of birth events (delivery after 40 weeks gestation, meconium aspiration syndrome, infection such as Group B Streptococcus) or with congenital heart lesions, which the extra blood flow through the pulmonary circulation can stress the pulmonary blood vessels (premature closure of blood vessels, pulmonary venous abnormalities). The most common cause of PPHN is meconium aspiration syndrome.
Risk factors for PPHN are male sex, black or Asian maternal race, abnormalities in maternal body mass index (overweight [BMI > 27] or underweight [BMI < 20]), diabetes, asthma, cesarean section, late preterm gestational age, large for gestational age status (LGA) and infection. Prenatal exposure to medications such as selective serotonin reuptake inhibitors (SSRIs, commonly used for depression treatment) have also been implicated in PPHN development; the effect of non-steroidal anti-inflammatory medications such as ibuprofen on PPHN is controversial.
Infants with PPHN will usually present within the first 24 hours of life with trouble breathing and low oxygen saturation levels. As mentioned above, they may also have symptoms to suggest other associated conditions. Tests such as chest X-rays, bloodwork and echocardiograms will be done to evaluate the infants thoroughly. The echocardiogram is the test used to make the diagnosis of PPHN, and it will show signs of elevated right ventricular pressure and abnormal shunting of blood through persistent fetal circulation vessels.
Treatment is generally aimed at supporting the heart and lungs as the PVR may continue to fall slowly. This consists of oxygen, intubation/mechanical ventilation, antibiotics, intravenous fluids, sedation and blood pressure support medications. In more difficult cases, inhaled nitric oxide may be needed to assist with PVR reduction. The use of medications commonly used in PH (sildenafil, bosentan, prostacyclins) are occasionally considered in these settings. For severe cases of PPHN, extracorporeal membrane oxygenation (ECMO) is used to maintain oxygen delivery to the body until the PVR falls.
Infants who survive PPHN will need to be followed by pediatric subspecialists such as pulmonologists and cardiologists. Many of the infants who survive PPHN will remain on some PH therapy upon discharge from the neonatal intensive care unit and will need to be managed by a PH specialist. Other specialists who may need to see PPHN survivors are developmental specialists and neurologists as there is an increased risk of developmental delays.
Answer provided by Nidhy Paulose Varghese, MD, Assistant Professor of Pediatrics, Division of Pulmonary Medicine Baylor, College of Medicine, Texas Children's Hospital
This article was first published in Pathlight Fall 2014.
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