In utero, the oxygen saturation of the fetus is 70% (hypoxic levels) and this stimulates erythropoietin, produces a reticulocytosis (3-7%), and increases red cell production causing a high hemoglobin at birth.
Table 2-5. Indications for Small-Volume RBC Transfusions in Preterm Infants
Transfuse infants at hematocrit <30%
c. If significant apnea (>6/day) and bradycardia are noted while receiving therapeutic doses of methylxanthines d. If heart rate >180 beats/min or respiratory rate >80 breaths/min persists for 24 hours e. If weight gain <10 g/day is observed over 4 days while receiving >100 kcal/kg/day f. If undergoing surgery
Transfuse for hematocrit <35%
a. If receiving >35% supplemental hood oxygen b. If intubated on CPAP or mechanical ventilation with mean airway pressure >6 cm H2O
Do not transfuse a. To replace blood removed for laboratory tests alone b. For low hematocrit value alone
Abbreviation: CPAP, continuous positive airway pressure by nasal or endotracheal route. Modified from Hume, H. Red blood cell transfusions for preterm infants: the role of evidence-based medicine. Semin Perinatol 1997;21:8-19, with permission.
After birth the oxygen saturation is 95%, EPO is undetectable, and red cell production by day 7 is 10% of the level in utero. As a result of this, the hemoglobin level falls to a nadir at 8-12 weeks (physiologic anemia). At this point oxygen delivery is impaired, erythropoietin stimulated, and red cell production increased.
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