ARTERIAL OXYGENATION AND PULMONARY ARTERIAL-PRESSURE IN HEALTHY NEONATES AND INFANTS AT HIGH-ALTITUDE

We sought to document arterial oxygen saturation relative to changes i n the right ventricular pressure/left ventricular pressure ratio (RVP/ LVP ratio), an index of pulmonary arterial pressure, in infants born a t high altitude. We performed pulse oximetry and echocardiography in 1 5 healthy infants born in Leadville, Colo. (3100 m), at 6 to 24 hours, 24 to 48 hours, 1 week, 2 months, and 4 months of age. Pulse oximetry was done under conditions of wakefulness, feeding, and active and qui et sleep. All infants received supplemental O2 at delivery and during postnatal transition; all oximetry measurements were performed with in fants breathing room air. The mean arterial O2 saturation ranged from 80.6% +/- 5.3% to 91.1% +/- 1.7% during the 4 months. Values fell duri ng the first week after birth and then rose gradually to attain near-b irth values at 2 and 4 months of age. Arterial O2 saturation was unifo rm among behavioral states at 6 to 24 hours and 24 to 48 hours of age. After 1 week of age, values were highest during wakefulness, intermed iate during feeding and active sleep, and lowest during quiet sleep. T he RVP/LVP ratio remained in the normal or mildly elevated range throu ghout the study period. We conclude that the RVP/LVP ratio promptly be comes normal at high altitude, and despite low arterial O2 saturation in the first weeks to months after birth, healthy newborn infants at 3 100 m show little evidence of acute pulmonary hypertension.