Systemic citrate load during continuous renal replacement therapy is not negligible and can be predicted using indirect methods
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KeywordsCitrate Continuous Renal Replacement Therapy Exact Method Polysulfone Citrate Concentration
Data on significance of systemic gain of citrate during continuous renal replacement therapy (CRRT) are missing. Direct citrate measurements are scarcely available. The quantification using a difference of unmeasured anions (UA) on the filter and the method using correlation between concentration of citrate (Cf) in effluent to the proportion of citrate flow to blood flow (Qc/Qb) were compared with the control exact methods.
A prospective controlled observational study was performed in a 20-bed general ICU. Patients on 2.2% acid-citrate-dextrose (ACD, n = 41) were compared with controls on unfractioned heparin (n = 17). All were treated with an Aquarius Baxter device on 1.9 m2 polysulfone filters. Samples were taken from a central venous catheter, ports pre filter and post filter and from dialysate/filtrate 24 hours after commencing with CRRT and 60 minutes later.
There were no significant differences (P > 0.05) between CVVH (n = 18) and CVVHDF (n = 23) in measured citratemias nor in systemic gain of citrate. The difference between post-filter and pre-filter UA correlated with difference of citrate concentrations (r2 = 0.66). Citrate gain was calculated as 31.5 ± 10.5 mmol/hour utilizing this relationship. Cf showed tight correlation with the Qc/Qb ratio (r2 = 0.72). Gain of citrate calculated as citrate input minus citrate removal (effluent flow × Cf) where the regression equation replaces Cf was 29.4 ± 7.2 mmol/hour. The first exact method used post-filter and pre-filter citrate concentrations multiplied by matching blood flows. Gain of citrate obtained by this method was 29.3 ± 11.0 mmol/hour. The second exact method deducted citrate removal (15.7 ± 5.9 mmol/hour) in effluent from citrate input (45.1 ± 8.8 mmol/hour) and produced a citrate gain of 29.3 ± 7.2 mmol/hour. Comparing two studied methods of citrate gain estimation with exact methods showed no significant differences (P = 0.5, Kruskal-Wallis ANOVA). Bland-Altman analysis showed no systematic bias in results.
Systemic load of citrate is not negligible and can be predicted without taking direct citrate levels. Proposed indirect methods showed reasonable accuracy in systemic citrate load estimation.
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