Fluid shift from intravascular compartment during fetal red blood cell transfusion

Intrauterine transfusion imposes a considerable burden on the fetal circulation by increasing volume and pressure, and a fluid shift from the fetal circulation occurs even during the procedure. The aim of this study was to quantify the intraprocedural fluid shift and to investigate the effect of procedural and fetal characteristics on this fluid shift.

In 95 alloimmunized pregnancies, we calculated fluid shift at the first intrauterine transfusion by determining initial and final blood volumes. We evaluated the association of the fluid shift with the speed and volume of the transfusion, the severity of anemia and the presence of hydrops.

Of the included fetuses, 11 were mildly hydropic and four were severely hydropic. A mean fluid shift of 36% of the transfused volume was found. Fluid shift related positively to transfused volume (P < 0.001). The percentage fluid shift of transfused volume was inversely related to the speed of transfusion (mL/kg/min) (P < 0.041) and was not related to the severity of anemia (P = 0.55) or to hydrops (P = 0.66). It was found that younger fetuses had been unintentionally subject to high volumes and speeds of transfusion relative to their size.

Around one-third of the transfused volume is lost from the intravascular compartment during the procedure of intrauterine transfusion. There is a large variation between fetuses, partly explained by the volume and speed of the transfusion. Neither severity of anemia nor hydrops plays a clear-cut role, and thus other factors may explain the variation in fluid shift. The probability that hematocrit will still increase after transfusion, as a result of a continuing fluid shift, should be considered in transfusion policy. Advice is given on gestational age-adjusted speed of transfusion.