Blood rheology in the newborn infant.

The blood in neonates shows several peculiar properties which affect its rheological properties. 1. The haematocrit in neonates may be as high as 0.65 l/l without any clinical signs. 2. Both plasma viscosity and red cell aggregation are markedly lower in neonates than in adults because of low protein levels in neonates. This results in decreased blood viscosity at given haematocrit, particularly at low shear forces. 3. Deformability of neonatal red cells is similar to that of adult cells when studied under controlled conditions (e.g. rheoscope, ektacytometer). However, neonatal red cells are less filterable and require higher pressures for entering narrow micropipettes than adult red cells due to the larger size of neonatal red cells. 4. Neonatal leukocytes require higher pressure for the passage of 5 microns filter pores or 5 microns micropipettes than adult cells. The following haemorheological disorders have been observed in neonates: 1. Polycythaemia in infants with late cord-clamping, severe asphyxia, growth retardation and diabetic mothers. 2. Markedly decreased red cell deformability in septicaemia, necrotizing enterocolitis and in vitamin E deficiency (after exposure to oxidizing agents). 3. Moderately decreased red cell deformability in infants with diabetic mothers, growth retardation and severe acidosis. 4. Increased red cell aggregation in septicaemia. 5. Lack of red cell aggregation in immature neonates. 6. Decreased ability of leukocytes from septic neonates to pass filter pores and micropipettes. Treatment may be either haemodilution (in polycythaemia) or exchange transfusion (in septicaemia and necrotizing enterocolitis). Haemorheological drugs have not been used in neonates.