Ionized hypocalcemia prior to continuous veno-venous hemodialysis initiation: prevalence and consequences

Regional citrate anticoagulation (RCA) is currently the first-line strategy during continuous renal replacement therapy (CRRT). No international recommendation exists concerning the assessment of ionized calcium (iCa) prior to RCA-CRRT initiation and data on the consequences of pre-existing ionized hypocalcemia are lacking. This study aimed to investigate the frequency of iCa measurements prior to RCA-CRRT and assess the consequences of ionized hypocalcemia in patients undergoing RCA-CRRT. This retrospective, single-center study included all patients treated with RCA-CRRT between June 2021 and April 2023. Calcium target range was considered achieved during RCA-CRRT when the iCa levels were stable within the protocol range (1.12-1.20 mmol/L) over two consecutive measurements performed in a 6-h timeframe. RCA-CRRT related adverse events were screened during the first 72 h of RCA-CRRT. Among the 200 patients screened, 117 (59%) had an iCa measurement prior to RCA-CRRT initiation. Among them, 70 (60%) had normal iCa concentration, 22 (19%) had hypocalcemia which was corrected by calcium chloride, and 25 (21%) had ionized hypocalcemia without any correction prior to CRRT initiation. In all patients presenting hypocalcemia, mean iCa reached normal values 12 h after RCA-CRRT initiation. Calcium target range was achieved in 59 (50%) patients within the first 72 h, whereas only 5 (4.3%) of subjects that remained on CRRT at 72 h failed to achieve homeostasis. Patients who presented with severe hypocalcemia (< 1 mmol/L) during the first 12 h of RCA-CRRT had more frequently pre-existing severe hypocalcemia. Ionized calcium blood measurement is not systematically performed prior to RCA-CRRT initiation. However, within the 12 h following RCA-CRRT initiation, most patients achieved normal calcium concentrations including those with pre-existing hypocalcemia.