UNEXPECTED CITRATE TOXICITY AND SEVERE HYPOCALCEMIA DURING APHERESIS

BACKGROUND: The citrate anticoagulant used during apheresis procedures is considered a safe medication because it is rapidly metabolized by the donor. However, acute, life-threatening hypocalcemia is possible i f the infusion rate of citrate is increased. CASE REPORT: A 54-year-ol d woman with metastatic breast cancer, but otherwise in good health, h ad just begun a fifth collection of hematopoietic peripheral blood pro genitor cells by leukapheresis. The instrument's self-loading apheresi s kit was primed uneventfully. Seven minutes into the procedure, the p atient developed signs and symptoms suggesting severe hypocalcemia, in cluding muscle spasms, chest pain, and hypotension. The citrate bag wa s discovered to have emptied, and a section or the anticoagulant tubin g was protruding outside of the rotary pump. The patient's ionized cal cium level was 0.64 mmol per L (normal range, 1.18-1.38 mmol/L). In su bsequent experiments where the anticoagulant tubing was either imprope rly loaded at the outset or partially pulled out of the rotary pump, n o instrument alarms sounded. CONCLUSION: Citrate toxicity and life-thr eatening hypocalcemia can occur if the anticoagulant line of an aphere sis instrument is riot properly housed in its rotary pump or becomes d isengaged during the procedure. Instrument manufacturers are encourage d to consider designs that allow the direct measurement of the volume of citrate delivered. In the interim, periodic visual and tactile conf irmation of tubing placement during apheresis procedures is prudent.