Removal kinetics of exchange transfusion.

where v is the total exchanged volume, V is the patient's blood volume and e is the transcendental number, base of the natural logarithm. However, he later stated that his formula was not correct because it did not take into consideration the difference between the patient's haematocrit and that of the transfused blood. Moreover, according to others, even when the two haematocrits happen to be the same, the formula should be modified to account for the difference between venous haematocrit and body haematocrit. Wiener also stated that it was obvious that, for an equal exchanged volume, exchange transfusion would be more efficient, the more the neonate was anaemic. Taken together, these opinions risk misleading the reader seriously. Wiener's formula describes a continuous flow exchange. However, during exchange transfusion, neonatal blood is replaced by donor blood, withdrawing and transfusing alternatively 5-20 mL of blood. The exchange is, therefore, intermittent. It can be demonstrated (see Appendix A) that when blood is first withdrawn and then transfused, at each cycle: