title: Proximally delivered dilute heparin does not improve circuit life in continuous venovenous haemodiafiltration.
abstract: OBJECTIVE
  To assess the effect on circuit life in continuous venovenous haemodiafiltration (CVVHD) by manipulating heparin dilution and point of administration.
  
  
  METHODS
  Repeated crossover design. Cases were randomised for first circuit and heparin dilution, after which crossovers occurred until treatment was stopped.
  
  
  METHODS
  A 24-bed combined general and surgical intensive care unit admitting 1900 patients a year. On average, 54 cases a year receive CVVHD.
  
  
  METHODS
  26 critically ill adult patients requiring CVVHD were enrolled, 18 of whom used at least one standard circuit and one modified circuit.
  
  
  METHODS
  Two circuit configurations and heparin dilutions were compared. In combination A, standard CVVHD blood lines and heparin concentration (100 units/ml) were used. In combination B, heparin was delivered in a more dilute volume (10 units/ml) via a modified circuit design with an administration port immediately adjacent to the venous access.
  
  
  RESULTS
  18 randomised crossovers of circuits A and B occurred. Mean/median circuit life for the standard heparin/circuit combination A was 20.1/17.5 (SD 14.6) and for the modified combination B 21.4/15.4 (SD 19.2). There was no significant difference between circuits (paired t-test, p = 0.8175). To identify other factors which could have influenced circuit life (platelet count, heparin dose and pre- and post-filter activated partial thromboplastin time, APTT) all circuits terminated for the reasons identified (n = 105) were analysed using linear modelling. Survival analysis was used to determine the survival function of the circuit. Pre-heparin APTT was the only factor associated with an increase in filter life (p = 0.035). The hazard rate for filter failure was 0.049/h (95% confidence interval 0.04 to 0.06), the range of time until filters failed was 1.8 to 78.5 h.
  
  
  CONCLUSIONS
  Proximally administered dilute heparin is not associated with a significant increase in circuit life.
authors.affiliation: Critical Care Division, Royal Perth Hospital, Western Australia.
authors.forename: G D
authors.initials: GD
authors.lastname: Leslie
authors.forename: I G
authors.initials: IG
authors.lastname: Jacobs
authors.forename: G M
authors.initials: GM
authors.lastname: Clarke
mesh_terms: D058186:Acute Kidney Injury / Q000628:therapy*; D000925:Anticoagulants / Q000627:therapeutic use*; D018592:Cross-Over Studies; D004868:Equipment Failure; D017583:Hemodiafiltration / Q000295:instrumentation* / Q000379:methods*; D006493:Heparin / Q000627:therapeutic use*; D006801:Humans; D016014:Linear Models; D016016:Proportional Hazards Models
chemical_list: D000925:Anticoagulants; D006493:Heparin