Red cell and plasma volume in newborn infants.

Schiicking (I1879) estimated the total blood volume of six newborn infants. In two infants, whose cords had been tied soon after delivery, blood volume was distinctly smaller than in four other infants whose cords had not been tied until some minutes after delivery. However, these estimates were made by Welcker's method and were by no means exact. The plasma volume of newborn infants was measured by Lucas and Dearing (1921) using brilliant vital red, with rather variable results. Robinow and Hamilton (1940), using the same method, found an inverse relationship between haematocrit and plasma volume, and noted that high blood volumes were slightly more common when the haematocrit was high. Estimations with the dye Evans blue were made by Brines, Gibson, and Kunkel (1941), and by Russell (1949), but both these studies were chiefly concerned with children rather than with very young infants. A more extensive study of the plasma volume of newborn infants was made by DeMarsh, Windle, and Alt (1942), who were particularly concerned with demonstrating the effects on blood volume of early and late tying of the cord. Total blood volume was calculated from plasma volume and venous haematocrit. Their findings may be summ as follows: in infants who were deprived of their placental blood by early clamping of the cord, the haematocrit did not rise after delivery; by contrast, in infants who recovered their placental blood, the venous haematocrit rose, on the average, from 510o to 610o within three hours of birth. The plasma volume three hours after birth was not significantly greater in infants recovering their placental blood than in those deprived of it-further evidence of the rapidity of the adjustment. Three days after birth the findings were substantially the same, that is, the average plasma volume in the two groups was almost identical but the venous haematocrit averaged 60°', in those infants who had recovered their placental blood and was only 510o in those who had been deprived of it. There were considerable variations between individual estimates. For example, in one infant whose blood volume was estimated on the first and third days of life, the figure was 408 ml. on the first day and 243 ml. on the third day. That this difference in the estimates was largely to be ascribed to experimental error is suggested by the observation that the venous haematocrit was substantially the same on the two occasions. One is bound to conclude that the method of plasma volume estimation carried rather a large error. Although the main conclusions of DeMarsh et al. on the effect of placental transfer appear to be soundly established, the figures for total blood volume published by them cannot be taken as a reliable guide to the true blood volume of newborn infants. It is now widely recognized that estimates of blood volume based on plasma volume and venous haematocrit are higher than the true values. Smith, Arnold, and Whipple (1921), who were perhaps the first to reach this conclusion, suggested that the discrepancy was due to the fact that the proportion of red cells was higher in large vessels than in the body as a whole. Hahn, Balfour, Ross, Bale, and Whipple (1941), and Gibson, Peacock, Seligman, and Sack (1946) estimated red cell volume using red cells tagged with radioactive iron. They found that these direct estimates were always lower than those deduced from measurements of plasma volume and venous haematocrit. Gibson et al. concluded that the ratio whole body haematocrit' venous haematocrit