Anemia of Prematurity

During the first two months after birth, the concentration of hemoglobin declines rapidly from the highest to the lowest values that occur at any period of development (1-6). The low point is termed the physiologic anemia of infancy. It is considered physiologic because it is characteristic of healthy infants, it occurs in the absence of any recognized nutritional deficiency, and there is no sustained response to blood transfusion. If the fall in hemoglobin concentration were an isolated phenomenon, it would significantly diminish the availability of oxygen to the tissues. However, while hemoglobin concentration is decreasing, there are other changes that lead to a progressive rightward shift of the oxygen equilibrium curve, permitting more oxygen to be released by hemoglobin at any given oxygen tension (7-9). While these modifications in oxygen delivery are taking place, there are concurrent changes in oxygen requirements. As the newborn adapts to an extrauterine environment, his oxygen needs progressively in­ crease (10-12), and he becomes less able to withstand oxygen lack (13). Therefore, if tissue oxygenation is to remain adequate, oxygen extraction and/or cardiac output must increase. In the otherwise healthy term infant, the adaptations in oxygen delivery during the first two months after birth are rarely associated with clinical evidence of hypoxia. However, in the premature infant, the fall in hemo­ globin concentration is more profound, and in some infants clinical evi­ dence suggests that O2 delivery is compromised and that a blood transfusion is required ( 1 416). Nevertheless, the rapidity of developmental changes that affect oxygen delivery and the complexity of their interactions has been an impediment to developing clear-cut criteria for transfusion. Conse­ quently, this is an area in which clinical practices vary widely. Regardless