ALVEOLAR-ARTERIAL O2 AND CO2 DIFFERENCES AND THEIR RELATION TO LUNG VOLUME IN THE NEWBORN

Abstract

Twenty-six premature and five full-term infants, ranging in birth weight from 860 to 4,040 gm and in age from 3 hours to 98 days, were the subjects of this study. Measurements of thoracic gas volume and determination of alveolar-arterial oxygen gradient and arterial-alveolar carbon dioxide gradient were performed. All infants showed a decrease in thoracic gas volume in the first days of life. The initial high thoracic gas volume is thought to be due to trapped gas. The ability to trap gas was demonstrated in a number of infants. In the full-term infant the decrease in thoracic gas volume is associated with improvement in lung function. In the premature infants the decrease in lung volume is associated with a persistently elevated alveolar-arterial oxygen gradient and in an inequality of perfusion and ventilation, as evidenced by the large arterial-alveolar carbon dioxide gradient. In a small group of infants increase in functional residual capacity produced by negative pressure around the chest resulted in a decrease in the carbon dioxide and oxygen gradients, indicating that the infant's lung volume is less than optimum. These observations characterize in physiological terms some of the respiratory difficulties in small premature infants.