Cyanosis in the Newborn
Martin H. Lees MD1
Douglas H. King MD2
1 Directs Pediatric Cardiology at Emanuel Hospital, Portland and is Professor of Pediatrics and Perinatology at Oregon Health Sciences University
2 Private practice in Portland, OR, and is a Clinical Instructor of Pediatrics at the University of Oregon School of Medicine, fellow in the American College of Cardiology
RECOGNITION OF CYANOSIS IN THE NEWBORN
Clinical cyanosis is chiefly dependent on the absolute concentration of reduced hemoglobin in the blood rather than on the oxygen saturation. Thus, when there is more than 3 g of reduced hemoglobin per deciliter of arterial blood, central cyanosis should be recognizable. The O2 saturation when clinical central cyanosis becomes apparent varies from about 62% when the hemoglobin is only 8 g/dL to about 88% saturation in the polycythemic infant with a hemoglobin of 24 g/dL.
The normal relative polycythemia of newborn infants (hemoglobin 14 to 20 g/dL), therefore, facilitates recognition of cyanosis.
Recognition of cyanosis in the newborn is rendered more difficult by the presence of fetal hemoglobin (Fig 1). The ratio of fetal to adult hemoglobin varies from infant to infant, and the proportions of each hemoglobin affect the oxygen saturation resulting at any give Pao2. Thus, if a baby with a pH of 7.4 and a temperature of 37°C has mostly adult hemoglobin, central cyanosis (arterial saturation 75% to 85%) will be observed at a Pao2 of 42 to 53 mm Hg, whereas if the baby has mostly fetal hemoglobin, central cyanosis will be observed at a Pao2 of 32 to 42 mm Hg. Thus, the newborn with a high proportion of fetal hemogolobin may have a serious reduction in oxygen tension before central cyanosis is clinically apparent.
