Chapter 11:	The Infant
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As the lungs expand with air, P02 rises, the pathway is straightened, and prostaglandins are metabolized. More blood is now able to flow through the pulmonary capillaries and less through the ductus. Catecholamine release, triggered by the delivery process and the cutting of the umbilical cord, causes active constriction of the ductus to begin. Flow through the ductus is furthered impeded by rising aortic pressure.

Following delivery, neonatal pulmonary artery pressure declines incrementally from an average mean pressure of 39mm Hg at ten hours, to about 29 mm Hg at 15 hours. During the same time frame, neonatal aortic pressure rises to between 80-100 mm Hg at 20 hours post delivery.

The normal newborn % shunt (20-25%) is considerably different from that of normal adults (5-10%), possibly due to continued leakage through the neonate's ductus and foramen ovale.

Neonate's average blood pressure varies according to gestational age and weight. The average neonatal systemic blood pressure at one hour is:

Average blood pressure at 12 hours is:

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