Proximally delivered dilute heparin does not improve circuit life in continuous venovenous haemodiafiltration

To assess the effect on circuit life in continuous venovenous haemodiafiltration (CVVHD) by manipulating heparin dilution and point of administration.

Repeated crossover design. Cases were randomised for first circuit and heparin dilution, after which crossovers occurred until treatment was stopped.

A 24-bed combined general and surgical intensive care unit admitting 1900 patients a year. On average, 54 cases a year receive CVVHD.

26 critically ill adult patients requiring CVVHD were enrolled, 18 of whom used at least one standard circuit and one modified circuit.

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.

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.

Proximally administered dilute heparin is not associated with a significant increase in circuit life.