新生児の凝血系

抄録

1) Term and preterm newborn infants have normal levels of fibrinogen, factor V and factor VIII procoagulant activity when compared to older children and adults, although the range of values is greater in the small premature infants. On the other hand, the levels of contact phase clotting factors (XII, XI, prekalikrein and high molecular weight kininogen), vitamin K dependent clotting factors (II, VII, IX and X), factor XIII and coagulant inhibitors (antithrombin III, protein C and protein S) of the newborn infants are uniformly decreased to the levels of 20∼60% of normal adult values. These levels are dependent on gestational age with lower levels seen in normal preterm infants than in normal term infants.
2) The overall fibrinolytic activity of newborn infants within a few days of birth is increased when compared to adults. In preterm infants, plasminogen levels range from 25 to 40% of normal adults. These levels increase with gestational age and the plasminogen levels of term infants approach the 40∼60% of normal adults. The α₂-plasmin inhibitor levels of term newborn infants are slightly decreased to levels of 80% of normal adults.
3) Term and preterm newborn infants at gestational ages of 27 to 40 weeks have platelet counts in the same range as normal older children and adults. Platelet aggregation in platelet rich plasma of newborn infants within a few days of birth is diminished to ADP, collagen and epinephrine. However, whole blood platelet aggregation and platelet retention to glass beads are normal in newborn infants.
4) Above mentioned findings indicate that the hemostatic and antithrombotic balance is unstable in newborn infants. Therefore, the incidences of both thrombotic disorders and hemorrhagic disorders are higher in newborn infants than in older children and adults.
5) Our recent study indicates that many infants dying from intracranial hemorrhage had evidence of hemostatic failure compatible with disseminated intravascular coagulation or vitamin K dependent coagulant factor deficiency.
The coagulation abnormality is suggested to be the major factor of deterioration and, in some cases, the etiologic factor of intracranial hemorrhage in newborn infants.
6) Therapy of gabexate mesilate (FOY) for newborn infants with disseminated intravascular coagulation was more effective than heparin therapy.