Anemia of prematurity. Current concepts in the issue of when to transfuse.

At no other time of life is the decision to transfuse potentially as difficult as in the newborn period. Superimposed upon complex "physiologic" changes in the ability to deliver and release oxygen are varying requirements among infants in terms of oxygen need. These are compounded by changes brought about as a direct consequence of frequent phlebotomy in the most ill of preterm infants. Despite the confusion overlying many of the changes occurring at this time of life, certain principles can be applied. Unlike that of the adult, an infant's ability to make oxygen available in response to a specific demand is almost as dependent upon the modifiers of oxygen uptake and release by hemoglobin as upon the hemoglobin concentration itself. These modifiers are constantly changing, sometimes in a predictable fashion, sometimes not. As discussed, some attention to the status of a particular infant's capability in providing oxygen relative to need will assist in the decision when to transfuse. If specific parameters of these assessments can not be determined, it may be necessary to proceed with transfusion based on the clinical presentation of an infant. With regard to the above, any infant sufficiently ill to require frequent blood sampling should have such blood losses replaced, certainly before ten percent of blood volume has been exceeded. This is particularly true in infants who are unable to maintain adequate arterial oxygen tensions with or without the use of supplemental inspired oxygen. At several weeks of age, when the clinical status of a preterm infant may have stabilized, transfusion may or may not be needed during the nadir of the anemia of prematurity. Infants who had been previously transfused or who had earlier received frequent simple transfusions should be able to tolerate lower levels of hemoglobin. Infants without compromised cardiopulmonary function and in whom no unusual metabolic needs exist are unlikely to be aided by transfusions when the hemoglobin concentration is greater than 10 to 11 g/dl. At lower levels of hemoglobin, simple calculations of "available oxygen" may be helpful when it is difficult to determine whether clinical signs and symptoms of anemia exist. Such signs and symptoms may include poor feeding, dyspnea, tachycardia, tachypnea, diminished activity, and pallor. Apnea has not unequivocably been shown to improve following transfusion. Clearly, our current concepts regarding indications for transfusion, even when based upon known principles of physiology, still represent an art form that is less than completely scientific.(ABSTRACT TRUNCATED AT 400 WORDS)