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To the Editor: In working with the exchange transfusion nomogram I have noted a practical point of help to the clinician working with a small or premature infant. Problems arise in reading the nomogram when the recipient blood volume is less than 400 cc because the straight edge seems to lie on top of several percentage points where it crosses the per cent exchange diagonal. In this case if the donor blood volume and recipient blood volume are each multiplied by ten the straight edge will cross the diagonal at an angle closer to 90 degrees, and the answer will be read more easily.
For example, a donor blood value of 200 cc and a recipient value of 200 cc result in an exchange transfusion of 63% (1:1 exchange). So does a value of 2,000 cc donor and 2,000 cc of recipient blood. However, the former is hard to read
TROSSMAN CM. READING NOMOGRAMS. Am J Dis Child. 1963;106(3):347. doi:10.1001/archpedi.1963.02080050349018