Ionized calcium buffering in the transfused anhepatic patient: Ab initio calculations of calcium ion concentrations

Homeostatic control of ionized calcium can be volatile during liver transplantation, particularly during the anhepatic stage. Recently, an opportunity arose to evaluate an 11-year-old girl who developed persistent ionic hypocalcemia during a prolonged anhepatic period subsequent to the failure and removal of the graft. The patient was remarkable for having survived a 34-hour anhepatic interval before a second and successful orthotopic liver transplant. Ionic hypocalcemia (ionized calcium less than 1 mmol per L) coexisted with significant hypercalcemia (total calcium greater than 5 mmol per L) during this anhepatic interval. The discrepancy was due to high concentrations of citrate, which accumulated from the multiple transfusions of citrated blood, and the inability to metabolize citrate in the anhepatic state. Using a mathematical model to solve for free calcium ion concentration in the presence of multiple ligands, it is demonstrated that prolonged hypercitricemia markedly alters the calcium ion buffering properties of blood, and these changes must be recognized in order to prevent adverse clinical consequences of ionic hypocalcemia.