Short-term effects of blood transfusion on blood volume and resting peripheral blood flow in preterm infants

The effects of blood transfusion on cardiac output and blood pressure are variable, but resting peripheral blood flow (RPBF) may be a sensitive indicator of changes in blood volume. The purpose of this investigation was to study the effects of red cell transfusion on blood volume (Evans blue), blood pressure, RPBF in the leg (strain-gauge plethysmography) and blood viscosity (cone-plate viscometer) in preterm infants during the first week after birth. Fourteen infants with mean ± SD birth weight of 1658 ± 429 g, gestational age 33 ± 3 weeks and postnatal age 64 ± 40 h received 18 ±4 ml/kg of packed red cells (red cells 11±2 ml/kg, plasma 7± 1 ml/kg) because their hematocrit was less than 0.45 l/l. Mean blood volume before transfusion was 88±15 ml/kg. The increase in blood volume (9 ±4 ml/kg) measured 4 to 6 h after transfusion was smaller than the transfused volume (18 ± 4 ml/kg), due to a shift of plasma to the extravascular space. The plasma shift increased with increasing pretransfusion blood volume ( r = 0.70; p = 0.007). Red cell transfusion caused an increase in RPBF by 25% ( p <0.01), whereas systolic blood pressure (BP) increased by only 12%. Peripheral resistance (R = BP/RPBF) decreased by 9% (p<0.01). Blood viscosity (±) increased by 21'% ( p <0.001) and vascular hindrance (R/±) decreased by 24% ( p < 0.001), indicating vasodilatation of limb arteries. The increase in RPBF and the decrease in hindrance were particularly pronounced in infants with high pretransfusion blood volume. We conclude that the increase in blood volume after transfusion is not proportional to the transfused volume and that RPBF increases more than systolic blood pressure with increasing blood volume. The increase in RPBF can be explained by vasodilatation of limb arteries and by increased blood pressure.