title: Circuit life versus bleeding risk: the impact of achieved activated partial thromboplastin time versus achieved filtration fraction.
abstract: Whilst prolonging hemofilter (circuit) life, heparin increases bleeding risk. The impact of achieved activated partial thromboplastin time (APTT) on circuit life and bleeding risk has not been assessed in a modern critically ill cohort. Lowering filtration fraction may be an alternative means of prolonging circuit life, but is often overlooked in critical care. An observational study of 309 consecutive circuits in a general intensive care unit was conducted using a wide target APTT range. Multilevel modeling was used to predict circuit life and bleeding according to achieved APTT and filtration fraction. Independent predictors of circuit failure (i.e. unplanned ending of treatment) included filtration fraction (P<0.001, HR 1.07 per 1% increase), peak APTT (P<0.001, HR 0.8 per 10 s increase or 0.3 APTR increase) and baseline PT (P=0.014, HR 0.91 for every 50% increase). The only significant predictor of bleeding was peak APTT (P=0.017, OR 1.05 per 10 s increase). Every 10 s APTT increase was associated with a 20% reduction in circuit failure, but a 5% increase in hemorrhage. A 3% reduction in filtration fraction was associated with the same improvement in circuit life as a 10 s increase in APTT. Increasing APTT prolongs circuit life but carries a substantial risk of bleeding even in modern practice. Filtration fraction has a large impact on circuit life in the critically ill: a 3% reduction in filtration fraction, e.g. by increasing blood flow or delivering some of the clearance via dialysis, would be expected to reduce circuit failure as much as a 10 s increase in APTT.
authors.affiliation: Adult Intensive Care Unit, Oxford University Hospitals NHS Trust, Oxford, UK.|Oxford Kidney Unit, Oxford University Hospitals NHS Trust, Oxford, UK.|Institute of Biomedical Engineering, Oxford University, Oxford, UK.
authors.forename: Clare
authors.initials: C
authors.lastname: MacEwen
authors.affiliation: Adult Intensive Care Unit, Oxford University Hospitals NHS Trust, Oxford, UK.|Institute of Biomedical Engineering, Oxford University, Oxford, UK.
authors.forename: Peter
authors.initials: P
authors.lastname: Watkinson
authors.affiliation: Oxford Kidney Unit, Oxford University Hospitals NHS Trust, Oxford, UK.
authors.forename: Christopher
authors.initials: C
authors.lastname: Winearls
mesh_terms: D000368:Aged; D000925:Anticoagulants / Q000008:administration & dosage* / Q000009:adverse effects; D016638:Critical Illness; D005260:Female; D006470:Hemorrhage / Q000139:chemically induced* / Q000453:epidemiology; D006493:Heparin / Q000008:administration & dosage* / Q000009:adverse effects; D006801:Humans; D007362:Intensive Care Units; D008297:Male; D008875:Middle Aged; D008962:Models, Theoretical; D010314:Partial Thromboplastin Time; D017582:Renal Replacement Therapy / Q000379:methods*; D012189:Retrospective Studies; D012306:Risk
chemical_list: D000925:Anticoagulants; D006493:Heparin
keywords: Anticoagulation; Circuit life; Filtration fraction; Hemofiltration; Unfractionated heparin