Abstract
Objective
To determine whether premature clotting of haemofiltration circuits could be related to heparin removal across the filter membrane into the ultrafiltrate.
Design
Randomised study using either unfractionated (n=8) or low molecular weight (n=7) heparin for anticoagulation of the haemofiltration circuit at 1000 and 600U/h respectively. Samples were drawn at 1 and 2 h from arterial and venous limbs of the haemofilter circuit for measurement of plasma heparin (as anti-Factor Xa activity), antithrombin III and haematocrit. Ultrafiltrate samples were collected at the same time for measurement of anti-Xa activity.
Setting
Intensive care unit.
Patients
Patients in acute renal failure requiring haemofiltration.
Results
Both unfractionated and low molecular weight heparin plasma levels were within the range required for therapeutic anticoaguation in all but one patient at 2 h. Ultrafiltrate anti-Xa levels were insignificant. Antithrombin III levels in these critically ill patients were subnormal in 11 of the 15 studies.
Conclusions
Despite their small sizes, neither unfractionated nor low molecular weight heparins cross the haemofilter membrane into the ultrafiltrate in any measurable quantity. Both heparins were present in plasma at a level suitable for therapeutic anticoagulation. Subnormal levels of antithrombin III may be an important factor in determining filter longevity.
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Singer, M., McNally, T., Screaton, G. et al. Heparin clearance during continuous veno-venous haemofiltration. Intensive Care Med 20, 212–215 (1994). https://doi.org/10.1007/BF01704703
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DOI: https://doi.org/10.1007/BF01704703