A Pilot Study of Antithrombin III Supplementation during Neonatal Extracorporeal Support (ECLS). † 219

Antithrombin III (AT III) activity may be low in infants with severe lung disease. We and others have reported that many infants develop circuit thrombosis during ECLS, with low fibrinogen and elevated fibrin degradation products (FDP). As heparin acts in conjunction with AT III to inhibit activated coagulation factors, low AT III activity may contribute to this process. We undertook a pilot study to determine 1) levels of AT III after initiation of ECLS, and 2) the effect of AT III supplementation. We studied 13 infants cannulated for ECLS at 44 ± 12 hours of life. In the first 6 hours of support, mean AT III activity was 25.7 ± 2.9% (range 10-43%), below the reported normal value for term infants (63%). Levels prior to ECLS did not differ significantly. Each infant received supplementation with AT III concentrate at a mean dosage of 47 ± 5 units/kg. Mean AT III activity measured 13.6 ± 2 hours following the initial dose was 70.3 ± 4%. One to four further AT III doses were given for activity levels below 40% during the first 7 days of ECLS. We compared heparin infusion rates, activated clotting times (ACTs) and incidence of hemorrhagic and thrombotic complications with 14 consecutive historical control infants supported at our institution during the previous 12 month period. Thrombotic complications were defined as need for complete circuit change for fibrinogen < 100 mg/dl and FDP > 40, or acute circuit failure. Results: Table Survival (10/13 vs 11/14) and ECLS duration (198 ± 28 vs 193 ± 24 hours) did not differ between the groups. Three of the thrombotic complications in the control group required emergent recannulation or circuit change. We conclude that AT III activity is low in infants prior to and immediately after cannulation for ECLS. AT III supplementation did not affect heparin dosage or mean ACT, and did not increase hemorrhagic complications during neonatal ECLS. It appears to reduce serious circuit thrombosis. A randomized trial will determine whether AT III supplementation is of benefit.

Table 1