46 ASAIO Journal 2012 One of the greatest problems in performing continuous renal replacement therapy (CRRT) is premature coagulation of the circuit. The aim of the current study was to monitor the circuit function prospectively and analyze patient-related variables that may affect circuit life. Critically ill patients admitted to the intensive care unit of a tertiary hospital between August 2010 and August 2011 receiving continuous veno-venous hemofiltration (CVVH) with systemic heparin anticoagulation were prospectively studied. Variables including body temper- ature, blood pH value, ionized calcium level, activated partial thromboplastin time (aPTT), prothrombin time (PT), platelet count, and heparin dose were collected and analyzed for their association with circuit life span. Fifty-four patients treated by CVVH were included, with 255 filters. The filter life was 29.7  13.4 hours (mean ± standard deviation [SD]). Circuits with longer survival time appeared to have lower body tem- perature (37.80  1.14 vs. 36.36  1.09; p , 0.05), lower levels of serum ionized calcium (0.80 vs. 1.29; p , 0.05), and to be more acidic (7.233 vs. 7.377; p , 0.05). Cox regres- sion showed that pH value and ionized calcium levels were significantly associated with circuit life. Other variables of hematocrit, albumin levels, platelet count, aPTT, PT, or dose of heparin were not significantly associated with circuit life. ASAIO Journal 2012; 58:46–50. Continuous renal replacement therapy (CRRT) has become an important treatment for critically ill patients with acute kid- ney injury, volume overload, and electrolyte derangement. It removes solutes in a continuous fashion without causing sig- nificant hemodynamic instability, which is an important factor that it outweighs the conventional renal replacement therapy in unstable patients. However, the therapeutic effectiveness of CRRT is heavily dependent on the continuity of the treatment. If the treatment is suspended because of inadequate circuit life, the clinical course and outcome of critically ill patients may be adversely affected. 1,2 Ronco et al. 3 suggested that the compromised therapeutic efficacy was because of inadequate solute clearance. In addition to the compromised therapeutic effect, other consequences caused by shortened circuit life span include blood loss, increased cost, and greater risk of hemodynamic instability in the connection. The most important factor underlying the premature cessa- tion of CRRT is coagulation or clot formation in the circuit. A few studies have investigated variables that may shorten circuit life span and found that variables such as CRRT mode, contact between blood and artificial surface, surface area of the filter, heparin dose, blood-air contact in air detection chamber, and heparin dose influenced the circuit life. 4–6 The indication for continuous venovenous hemofiltration (CVVH) with higher vol- ume predilution is reasonable when the previous circuit is pre- maturely clotted. However, evidence is still lacking in this field and many potential factors that theoretically may enhance the coagulation process, such as fibrin, albumin, and ionized cal- cium remain unexplored. Thus, we conducted this prospective cohort study to determine variables that may affect circuit life. Methods Setting and Study Population A prospective observational study was conducted in a ter- tiary 18 bed intensive care unit (ICU) from August 2010 to August 2011. Patients were consecutively enrolled. Critically ill patients admitted to the ICU and requiring CRRT were eligible for assessment. Inclusion criteria were as follows: 1) patients who were older than 18 years, 2) underwent CVVH, and 3) with expected ICU length of stay of more than 72 hours. Patients who were pregnant, older than 80 years, contraindicated to systemic heparin anticoagulation (including suspected hepa- rin-induced thrombocytopenia, high risk of bleeding), or with preexistent severe coagulopathy were excluded. Data of filters that must be changed because of circuit coagulation or filter clogging were collected. Clotting was defined as the presence of visible clot in the circuit or persistent transmembrane pres- sure of greater than 280 mmHg, resulting in repeated trigger- ing of the pressure alarm. Filters that were electively changed because of examinations, procedures, and patient death within 48 hours were excluded. The study was approved by the local ethnic committee, and registered in ChiCTR (Chinese Clinical Trial Registry; ChiCTR-OCH-10001281). Because of its obser- vational nature, informed consent was waived. Kidney Support/Dialysis/Vascular Access Variables Associated with Circuit Life Span in Critically Ill Patients Undergoing Continuous Renal Replacement Therapy: A Prospective Observational Study ZHONGHENG ZHANG, HONGYING NI, AND BAOLONG LU From the Department of Critical Care Medicine, Jinhua Municipal Central Hospital, Zhejiang, P.R. China. Submitted for consideration August 2011; accepted for publication in revised form November 2011. Disclosure: The authors have no conflicts of interest to report. Reprint Requests: Dr. Zhongheng Zhang, No. 351, Mingyue Road, Jinhua, Zhejiang Province 321000, China. Email: zh_zhang1984@ hotmail.com. Copyright © 2012 by the American Society for Artificial Internal Organs DOI: 10.1097/MAT.0b013e31823fdf20