Filter lifespan in critically ill adults receiving continuous renal replacement therapy: The effect of patient and treatment-related variables

Objective: To examine the effects of patient and treatmentrelated variables on filter lifespan in critically ill adults receiving continuous renal replacement therapy (CRRT). Design and setting: This was a single-centre, retrospective, observational study conducted in a tertiary referral centre in metropolitan Melbourne, Australia. All CRRT filters used over a 44-month period from 1 January 2008 to 31 August 2011 were assessed for their hours of function before being stopped non-electively (due to clotting) or electively. Analyses were performed primarily for all CRRT filters and secondarily for those ceased non-electively during the study period. To assess for any relationship with filter life, we performed multivariable regression analyses for blood flow rate, anticoagulation type, vascular access site, vascular catheter type, reason for stopping the filter circuit, platelet count and activated partial prothrombin time. Results: A total of 1332 treatments in 355 patients were assessed for filter life. Of these, 474 were electively ceased, leaving 858 filter circuits for secondary analysis. In both analyses, higher blood flow rate predicted longer filter lifespan (P=0.03 for all filters and P=0.04 for non-electively ceased filters). Vascular catheter type was predictive of increased filter lifespan in the non-electively ceased filters (P=0.002) but not on analysis of all filters. Type of anticoagulation and vascular access site were not predictive of filter lifespan in either analysis. Of the patient haematological variables, only platelet count was predictive of increased filter lifespan (P=0.003 for all filters and P< 0.001 for non-electively ceased filters). Conclusions: Our study found that an increased CRRT filter lifespan is associated with higher blood flow rates and lower platelet count. Vascular catheter design may also be a factor.