Ionized calcium changes in adult patients undergoing therapeutic plasma exchanges

Ionized calcium [Ca^2 + ] is the free active form found in circulation used to monitor a patient's calcium during therapeutic plasma exchange (TPE). Hypocalcemia during TPE is caused by citrate anticoagulation. Citrate toxicity can be mitigated by calcium supplementation; however, there is no standard protocol for its use. We describe our institutional experience using calcium supplementation during TPE.

A retrospective review was conducted for patients who underwent TPE procedures between 10/01/2023 and 4/30/2025. Patients' age, gender, TPE indication, procedure duration, pre- and post-procedure [Ca²⁺], plasma volume, and calcium supplementation dose were analyzed.

[Ca²⁺] change across TPE procedures ranged between -0.65-0.74 mmol/L with a mean of 0.03 + 0.11 mmol/L. [Ca²⁺] changes followed a normal distribution with 95 % of [Ca²⁺] occurring between -0.19 and 0.24 mmol/L. Procedure duration and plasma fluid replacement percentage did not influence [Ca²⁺] changes. By contrast, significant [Ca²⁺] changes were seen based on calcium gluconate replacement dosage. A higher dose of calcium gluconate (1.65 g/L of plasma exchanged) showed a significant average [Ca²⁺] increase of 0.06 mmol/L (p < 0.001) compared to the normal calcium gluconate dose (1.5 g/L of plasma exchanged). Gender had statistically significant effects on [Ca²⁺] but the effect of TPE indication remains to be elucidated.

Use of prophylactic calcium during TPE is the major variable governing [Ca²⁺] changes during the procedure with minor contribution from patients' gender and TPE indication. A dose of at least 1.5 g/L prevented excessive decrease in [Ca²⁺] and reduced occurrence of citrate toxicity.