The significance of ionized calcium in cardiac and critical care. Availability and critical limits at US medical centers and children's hospitals.

The clinical use of ionized calcium has increased since the recognition of its importance in cardiac and critical care medicine. However, more than half the general medical centers in the United States do not provide immediate testing of ionized calcium levels in patients in critical care settings, although indications for this test indicate that they should. The following objectives were used in this study: (1) to determine the availability of ionized calcium testing; (2) to document appropriate critical limits; and (3) to describe the significance of ionized hypocalcemia in cardiac and critical care. The participants were 100 medical centers and 40 children's hospitals in the United States. At medical centers, mean (+/- SD) critical limits were as follows: low, 0.82 +/- 0.14 mmol/L (3.29 +/- 0.56 mg/dL); and high, 1.55 +/- 0.19 mmol/L (6.21 +/- 0.76 mg/dL). At children's hospitals, mean critical limits were as follows: low, 0.85 +/- 0.13 mmol/L (3.41 +/- 0.52 mg/dL); and high, 1.53 +/- 0.11 mmol/L (6.13 +/- 0.44 mg/dL). In the past decade, the availability of ionized calcium testing increased dramatically. Now, 57%, 86%, 95%, and 100% of general hospitals, heart transplant centers, children's hospitals, and pediatric heart transplant centers, respectively, perform testing in house. Collective experience indicates that: (1) aggressive monitoring of ionized calcium prevents cardiac (and neurologic) catastrophes, (2) appropriate levels optimize cardiac function, and (3) calcium repletion is safest when based on acute trends measured directly in whole blood. Hospitals should provide rapid response testing needed during transplantation and massive transfusion and for the diagnosis and treatment of acute ionized hypocalcemia.