ABSTRACT. Current guidelines for heparin therapy in pediatric patients have been extrapolated from trials in adult patients without rigorous evaluation of efficacy and safety. We prospectively monitored consecutive pediatric patients receiving systemic doses of heparin over 10 mo at one institution using a predetermined nomogram to monitor maintenance therapy. Sixty-five consecutive children; 38 males and 27 females, received systemic doses of heparin.Thirty children had deep venous thrombosis and/or pulmonary embolism; l l had arterial thrombi, most frequently after diagnostic angiography; and the remaining 24 received heparin prophylactically, for congenital heart disease. Twenty-nine (45%) of the 65 patients were less than 1 y of age and 22 (34%) were 10 y or older. Congenital heart disease was the predominant diagnosis under 1 y and deep venous thrombosis in older children. After a bolus dose of 50 U/kg, 39% of children (n = 30) achieved a minimal level activated partial thromboplastin time ( A m ) . Sixty-eight percent of children achieved a minimal level A P l T by 24 h and 81% by 48 h. For all 65 children, A P l T values were within the therapeutic range 43% of the time. APTT values outside the therapeutic range were twice as likely to be low as high. The average amount of heparin required to maintain therapeutic A P l T values for children was 22 UFglh: 28 U/kg/h for infants

Megakaryoblastic leukemia and transient leukemia in Down's syndrome have been reviewed using case reports from the literature and our own experience at the Hospital for Sick Children. The following conclusions have been reached: (1) approximately 20% of leukemia (excluding transient leukemia) in Down's syndrome is acute megakaryoblastic leukemia; (2) approximately 20% of all leukemia in Down's syndrome is transient leukemia; (3) transient leukemia in Down's syndrome is acute megakaryoblastic leukemia; (4) recurrence of acute megakaryoblastic leukemia occurs in 20% of the cases of transient leukemia; and (5) the incidence of acute megakaryoblastic leukemia in Down's syndrome is estimated to be 400 times that in normal children. These observations suggest that a specific form of leukemia, namely acute megakaryoblastic leukemia, has a remarkable association with Down's syndrome.

Twenty-four patients with Down syndrome and leukemia were studied. A strong male predominance (79%) was found. Age ranged between 18 months and 15 years (mean: 5 6/12); 54% of the patients were less than 4 years of age at the time of diagnosis. A preleukemic phase was noted in 6/24 patients. This phase, characterized essentially by thrombocytopenia, lasted from 2-8 months. Patients with preleukemia had unusual blast cell morphology and involvement of more than one cell line (dyserythropoiesis, hypolobulated megakaryocytes) and were probably M7 leukemias. All patients demonstrated severe methotrexate toxicity at standard methotrexate doses. Toxicity, manifesting as mouth ulcerations and bone marrow depression was seen regardless of the route of administration (oral, intrathecal or intravenous). A 30%-50% reduction of the standard dose was tolerated. Methotrexate absorption and clearance were studied in two patients and were found to be normal. We postulate that the observed toxicity of methotrexate may be due to a gene dosage effect for enzymes known to be on chromosome 21 and intervening in purine metabolism. Increased purine synthesis implies greater tetrahydrofolic acid demands and therefore greater sensitivity to an antifolate agent.

The incidence of acquired vWD in association with Wilms' tumor merits further study through a large prospective trial. Such a trial should include careful family and clinical bleeding histories plus measurement of a platelet count, BT, coagulant FVIII and vWF levels, RCoF activity, and vWF multimer analysis. The response to 1-desamino-8-D-arginine vasopressin (DDAVP) should be tested in all patients with Wilms' tumor and acquired vWD, including patients with a type III profile, before an invasive procedure is performed. Successful use of DDAVP may avoid exposure of affected patients to blood products.

Children undergoing major craniofacial surgery (MCFS) oftenHyperkalaemia is a recognized complication of massive blood transfusion with whole blood. Both the quantity of blood transfused and the rate of blood transfusion have been identified as risk factors.L-4Since the introduction of blood component therapy in the 1970's, all whole blood donations are separated into specific cellular and plasma components for storage. Therefore blood loss during surgery requires transfusion of each blood component. Massive transfusion with red blood cell concentrates (RBCconc) is not believed to carry the same risk of hyperkalaemia as does transfusion with whole blood because the amount of extracellular potassium per unit of RBCconc is believed to be small. 3'5 However, the plasma [K +] in units of RBCconc has been measured to be in excess of 30 mmol. L-1, and thus the extracellular mass of potassium in a unit of RBCconc may be of clinical importance even though the plasma volume in the unit is small. 6-8Our hypothesis was that massive blood transfusion with RBCconc presented a clinically important potassium load. Children undergoing major craniofacial surgery may require blood transfusion in excess of one blood volume. In addition some of these children have been observed to have high intraoperative plasma [K § Therefore children undergoing major craniofacial surgery (MCFS) were the focus of our investigation. The study is presented in two parts. The first is a retrospective chart CAN J ANAESTH 1990/ 37:4 /pp401-8