Factor XI kinetics after plasma exchange in severe factor XI deficiency.

Plasma exchange in a patient with factor XI deficiency allowed the determination of the factor XI disappearance time. The decay curve showed a biphasic pattern with a t1/2 of h. After a loading dose by means of plasma exchange with fresh frozen plasma (FFP) up to a factor XI level of 65%, administration of 0.5 liter FFP every 12 h was necessary to maintain the factor XI concentration between 40 and 60%. The clearances of factor XI, calculated from the results of plasma exchange and from the maintenance dose, correlated very well and showed that the t1/2 of factor XI did not change after surgery. The patient underwent major surgery uneventfully but ultimately died 3 1/2 weeks after operation from cerebral damage due to cardiac arrest, which occurred on the 2nd postoperative day.