Blood flow reductions during continuous renal replacement therapy and circuit life

Objective: Reductions in blood flow rate may occur undetected during peristaltic pumping of blood through continuous renal replacement therapy circuits. We investigated whether undetected reductions in blood flow rate occur during continuous veno-venous haemofiltration, and whether they are correlated with filter life. Patients: Twelve patients receiving continuous veno-venous haemofiltration in the intensive care unit of a tertiary hospital. Methods: Extracorporeal circuit blood flow during haemofiltration was continuously monitored utilizing a miniature ultrasound Doppler device. Otherwise undetected blood flow reductions were identified at severity levels of between 20% and 100% less than the set diastolic flow rate (83 ml/min). Information on anticoagulation status was simultaneously obtained. The frequency and severity of blood flow reductions were recorded, and the correlation with filter life was determined. Measurements and results: The duration of filter life ranged from 1.5 to 53 h, with a mean functional life of 19.62+/-16.32 h. There were 314 episodes of blood flow reduction during the 525 h of monitoring (0.59 episodes/h). There was a significant inverse relationship between the number of medium-level blood flow reductions and filter life. This correlation was much stronger than that between APTT and filter life. Conclusions: Undetected blood flow reductions occur during continuous veno-venous haemofiltration. Such reductions are frequent, and when sufficiently severe appear to be correlated with filter life more strongly than the blood coagulation variables typically used to monitor adequacy of anticoagulation and promote filter longevity.