Ovine fetal cardiovascular responses to packed red blood cell transfusions.

Fifteen transfusions were performed in normal or anemic chronically catheterized sheep fetuses ranging in weight from 0.73 to 3.62 kg and in age from 91 to 135 days' gestation (term = 147 days). During the transfusions, an average of 29.0 +/- 2.5 (SE) ml/kg of packed maternal red blood cells (hematocrit = 78%) were given intravenously over 30 minutes and fetal hematocrit increased from 28.5% +/- 1.2% to 43.8% +/- 1.6%. Circulating blood volume increased by 13.9 +/- 2.3 ml/kg at 1 hour after transfusion and remained at this level at 24 hours. An average of 15.1 +/- 2.4 ml/kg of plasma was lost from the circulation at 1 hour after the transfusion. Fetal vascular pressures increased significantly during the transfusions and the rise in arterial pressure was greater than that in venous pressure (p less than 10(-6]. Heart rate decreased by 23 beats/min at the end of the transfusion and remained 13 beats/min below control after 1 hour (p less than 10(-6]. From the measured blood volume changes, formulas were developed so that the fetal blood volume before the transfusion and the posttransfusion hematocrit could be accurately calculated (r greater than 0.90). Thus this study shows that packed cell transfusions increase fetal blood volume by only 50% of the transfused volume because of a loss of plasma from the circulation and that the pretransfusion blood volume and the posttransfusion hematocrit can be accurately calculated from readily measured variables.