Use of an intravascular gas exchanger: is low systemic heparinization safe?

Abstract

Extracorporeal membrane oxygenation (ECMO) is a cumbersome procedure. Alternatively, mechanical lung assist can be realized with an intravascular gas exchanger (IVOX). To assess the degree of initial anticoagulation required during intravascular lung assist, we evaluated two regimens of systemic heparinization in 10 bovine experiments. The animals were randomly assigned to two groups with either full systemic heparinization (heparin loading dose 300 IU/kg bodyweight; activated coagulation time (ACT) > 480 s) or low systemic heparinization (heparin loading dose 100 IU/kg bodyweight; ACT > 180 s). The surface heparinized intravascular gas exchanger was placed in the caval axis under fluoroscopic control, and a standard battery of blood samples was drawn before and at regular intervals during the procedure. After six hours of intravascular lung assist the device was explanted, drained, weighed, and carefully analysed. Preassist haematocrit was 25 ± 5% for full versus 24 ± 7% for low (NS) as compared with 23 ± 8% for full versus 26 ± 3% for low (NS) postassist. Platelet levels were 100 ± 25 for full versus 100 ± 21 % for low (NS) preassist as compared with 64 ± 22% for full versus 78 ± 22% for low (NS) postassist. Mean ACT was 157 ± 12 s for full versus 158 ± 18 for low (NS) preassist as compared with 800 ± 244 s versus 219 ± 25 for low (p < 0.05) postassist. Thrombin time was 20 ± 2 s for full versus 23 ± 2 s for low (NS) as compared with > 200 s for both groups after assist. Relative fibrinopeptide A levels were 7.3 ± 1.1 ng/ml for full versus 6.3 ± 1.6 ng/ml for low (NS) preassist as compared with 4.7 ± 4.1 ng/ml for full versus 5.8 ± 0.9 ng/ml for low (NS) postassist. CO₂ transfer was 40 ± 10 ml/min for full versus 36 ± 10 ml/min for low (NS) at the begining as compared with 45 ± 25 ml/min for full versus 46 ± 15 for low (NS) at the end. Weight increase due to device deposits (clots) was 14 ± 11 g for full versus 13 ± 10 g for low systemic heparinization (NS). Intravascular lung assist with low versus full systemic heparinization appeared to result in similar activation of the coagulation system, device deposits and gas transfer rates. Considering our clinical experience we can say that application of the device with reduced systemic heparinization is useful in selected patients.

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