Since the adoption of exchange transfusion as a method in the treatment of newborn infants with severe erythroblastosis (1-3) the question of the possible toxic effects of sodium citrate added to the administered blood, to prevent coagulation, has arisen (4). In this procedure from 85 to 95% of the infant's Rh-positive erythrocytes are replaced by the donor's Rh-negative erythrocytes depending upon the volume of blood that is administered and simultaneously removed (5). In order to effectuate

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... exchange of 85%o, a quantity of blood equivalent to twice the infant's blood volume must be used, and for an exchange of 98%o, a quantity of blood equivalent to four times the blood volume must be used. Since the average newborn infant has a blood volume in the range of 250-300 ml. the procedure involves the use of approximately 500 ml. and approximately 1,000 ml., respectively. With the use of sodium citrate as an anticoagulant the infant receives as much as 60 to 120 ml. of a 3%o solution of sodium citrate intravenously over a period of about 1½/2 hours. In the experimental animal, the intravenous administration of large quantities of sodium citrate has been shown to produce convulsions (6). This has been ascribed to the formation of a poorly ionized calcium citrate complex which removes calcium ion from the blood stream (7-9). Despite this consideration, exchange transfusions have been successfully carried out in a large number of cases, although occasionally deaths have been reported in the very severely affected cases (10). In order to study the adjustment that the newborn makes to the physiological strains to which it is subjected when an exchange transfusion is 1 The third in a series on the mechanism controlling citric acid levels in the blood. The first two papers in this carried out, citric acid, calcium, phosphorus, protein and total base levels were studied before, during and after such a transfusion on a newborn with no symptoms of erythroblastosis and with apparent normal hepatic and kidney function. The newborn studied was a mongolian idiot born in normal delivery. In addition citric acid determinations were carried out on serial bloods withdrawn from eight erythroblastotic infants during exchange transfusion. 500 ml. of blood were freshly drawn from a compatible donor. To this were added 60 ml. of 3%o sodium citrate dehydratee of tri-sodium citrate). This made a total volume of 560 ml. Over a period of approximately 60 minutes 500 ml. of. this citrated blood were infused into the saphenous vein at the ankle. After 60 ml. had been infused the radial artery was cut and the blood was collected in 60 ml. portions, during the progress of the transfusion. The first 60 ml. were added without removal of blood in order to dilate the blood vessels and make the radial artery more apparent. The cells were separated by centrifuging and the plasma was analyzed for the various blood constituents. Citrate determinations were carried out by a method previously described (11, 12) . Calcium was done by direct precipitation from plasma (13) without ashing. Where citrate was at a high level the results were later shown to be significantly low because of the interference of citrate with calcium precipitation. The determinations could not be repeated with ashing subsequently because calcium salts were found precipitated in the plasma on standing. The calcium results were discarded and are not reported except where the citrate levels were low enough so as not to interfere, or where analysis was done by ashing on plasma from freshly drawn blood. Phosphorus was determined calorimetrically (14), total protein by a modified biuret method (15) and total base by electrodialysis (16). The results obtained on the blood of the donor with added citrate, and on that of the newborn with no symptoms of erythroblastosis are shown before and after the tranfusion in Table I . The results are averages of duplicates. Standards and recovery of added amounts of the constituents 474