Reliability of monitoring acid-base and electrolyte parameters through circuit lines during regional citrate anticoagulation-continuous renal replacement therapy

Background The current practice involves blood sampling from the circuit line to measure acid-base and electrolyte parameters during continuous renal replacement therapy (CRRT). However, there is limited evidence supporting its reliability due to the effects of anticoagulant mechanism and access recirculation associated with regional citrate anticoagulation (RCA). Aim To evaluate the reliability of monitoring acid-base and electrolyte parameters through circuit lines in regular and reversed connections during RCA-CRRT. Study design In this prospective cohort study, we included critically ill patients receiving RCA-CRRT via a double-lumen catheter. During the second hour after CRRT initiation, we collected blood samples to monitor acid-base and electrolyte parameters and their levels were compared between samples from the circuit lines (at 0, 3, and 5 minutes) and those from the central venous catheter (CVC) line (at 0 minute). During this time, CRRT switched to the replacement state as controls. Results We observed 128 CRRT circuits in 60 adult patients receiving RCA-CRRT. Ninety-eight (76.6%) circuits had regular connections, while 30 (23.4%) had reversed connections. Among regular connections, no differences were observed in any acid-base or electrolyte parameters between samples from the CVC line and those from the circuit line at all time points (P > .05). Among reversed connections, ionized calcium levels were dramatically decreased at all three time points in samples from the circuit line compared with those from the CVC line (0.65 +/- 0.12, 0.72 +/- 0.11, and 0.78 +/- 0.99 vs 0.98 +/- 0.07 mmol/L, P < .001), with comparable levels of other acid-base or electrolyte parameters between the sampling patterns (P > .05). Conclusions Acid-base and electrolyte parameters could be reliably monitored through the circuit line during RCA-CRRT in regular connections. However, in reversed connections, pre-filter ionized calcium concentrations determined through the circuit line were lower than those determined through the CVC line. Relevance to clinical practice We suggest sampling from arterial or CVC lines rather than from the circuit line in a reversed connection during RCA-CRRT.