Red cell and plasma volume in newborn infants

Abstract

Estimations of plasma volume (using T-1824) or red cell volume (using labelled red cells) have been made in 53 newborn infants, of which 38 were normal and 15 affected with haemolytic disease of the newborn. In 38 infants both plasma volume and red cell volume were estimated. In 34 normal infants the average plasma volume was 41.3 ml./kg. However, plasma volume was not independent of haematocrit but on the contrary rose steadily throughout the venous haematocrit range 66 . 2 - 37 . 0. In four infants with haematocrits between 17.9 and 21.2, plasma volume was disproportionately raised, but these infants were in cardiac failure. Red cell volume was measured in 44 infants. The relationship between venous haematocrit and red cell volume was approximately linear when the venous haematocrit was below 55°o. However, above this level the venous haematocrit did not rise proportionately to the true red cell volume. The total blood volume of 28 normal newborn infants, deduced from measurements of plasma volume and red cell volume, was 84.7 ml./kg. On theoretical grounds blood volume is expected to increase with venous haematocrit, but this relationship could not be demonstrated conclusively in the present cases. The ratio of the 'whole body haematocrit,' that is total red cell volume/total blood volume to the venous haematocrit was found to be a constant in the venous haematocrit range 17.9% - 66.2°o. The value of the constant in this series was 0.87. Provided that the venous haematocrit is first multiplied by this constant, estimates of red cell volume obtained by the dye-haematocrit method agree satisfactorily with estimates made by labelled red cell methods.