Erythropheresis in children with polycythaemia.

Using a hypothetical formula to calculate exchange volumes, erythropheresis was performed on 47 occasions in 20 children with secondary polycythaemia. Following this procedure the mean haematocrit in the patients was reduced from 69.0 to 58.0% (P less than 0.001), and the individual haematocrit to 61% or below. In 39 (83%) of the 47 exchanges the reduction coefficient, i.e., the volume of exchange which effected a unit reduction in the haematocrit, ranged from 1.0 to 3.0 ml/kg bodyweight. The derivation of these coefficients facilitated the formulation of an equation which expresses the volume of blood (V) that needs to be exchanged in a patient in terms of his weight, observed haematocrit (Hct1) desired haematocrit (Hct2) and the reduction coefficient (RC): V = Bodyweight (kg) X (Hct1 - Hct2) X RC. Haematocrit rebound occurred after 83% 50% and 14% of 30-min, 60-min and 90-min exchanges, respectively, indicating that the optimal duration of the procedure should be between 60 and 90 min. Hypercyanotic spells complicated two of the 47 exchanges and one patient suffered a fatal micturition-related cardiovascular collapse shortly after erythropheresis.