To the Editor:
There are three points we would add to the excellent review article by Carton et al. [1,2].
The first deals with the differences between adult and infant coagulation. Normal adult levels of vitamin K-dependent clotting factors may not be reached for several weeks in the normal neonate. During the first few days of life, the already decreased levels of factors VII, IX, and X and prothrombin become progressively lower, and this decrease can be prevented by administering vitamin K . Other vitamin K-dependent proteins synthesized by the liver include proteins C and S. Protein C inhibits the function of factors VIII and V and enhances fibrinolysis; these properties are enhanced by protein S. Protein C is significantly reduced in plasma from healthy, full-term, newborn infants and remains below levels found in serum from adults for at least 6 mo . Protein S concentrations are reduced but increase to within the range found in normal adult plasma by 3 mo of age .
The second deals with the hypercoagulable state seen postoperatively. After liver transplantation in children, a decrease occurs in the plasma concentrations of both protein C and antithrombin III to below 50% of normal values and persists for 10 days. A similar prolonged decrease is not seen in adults. Immediately after surgery, a 10-fold increase in plasminogen-activator inhibitor occurs, with a further increase 6-9 days later. Therefore, between Days 4 and 10 in the immediate postoperative period, children are at an increased risk of thrombosis . An attempt to minimize this occurrence has resulted in the administration of anticoagulation therapy: intravenous heparin, dextran 40, aspirin , and antithrombin III .
The last point deals with the thrombosis of the hepatic artery. Although pediatric liver transplantation results in postoperative complications similar to adult transplantation, thrombosis of the hepatic artery seems to be the most common serious complication after liver transplantation in children. The incidence has been reported in 15% of the whole pediatric series ; it is more frequent when younger and smaller children undergo transplantation. The study by Tan et al.  reported an incidence of 23% of children younger than 3 yr and weighing less than 15 kg; in grafts from children younger than 3 yr or weighing less than 15 kg, the rate was 38%, and it increased to 67% when livers were transplanted from infants and neonates. When a reduced-size liver is used , thrombosis is relatively rare (5%), similar to the adult rate, and the survival is comparable to patients receiving whole livers. This technique has benefits: it allows anastomosis with larger vessels ; it uses livers without the coagulation problems of the infant and neonate grafts that we pointed out above; and it decreases waiting list mortality from almost 30% to 5% . But this technique has some drawbacks; the major drawback to hepatic size reduction was the increased amount of intraoperative blood loss .
We asked Dr. Carton for a response but failed to obtain one.
Antonio Abengochea, MD*
Juan J. Vila, MD, PhD dagger
Jesus Jimenez, MD double dagger
Juan Arago, MD, PhD*
Raul Varas, MD, PhD*
Emilio Monteagudo, MD, PhD section sign
Emilia Garcia, MD*
Departments of Anesthesiology and *Pediatric Intensive Care, dagger Pediatric Surgery, and Pediatric Hematology, Hospital Infuntil La Fe, Valencia 46009, Spain, and double dagger Department of Pediatrics, Hospital Materno Infantil Reina Sofia, Cordoba, Spain
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