Ionized calcium levels in critically ill surgical patients.

Ionized calcium levels measured in 74 critically ill surgical patients averaged 1.97 +/- 0.25 mEq/l, significantly lower than the average (2.26 +/- 0.14) in 34 healthy individuals. The mortality rate increased as ionized calcium levels decreased. Of four patients with ionized calcium levels lower than 1.40 mEq/l, none survived. The average total calcium (4.0u mEq/l) in the critically ill patient was also significantly lower than in controls (4.55 +/- 0.40 mEq/l). The albumin levels were severely reduced (2.80 +/- 0.59 mg/dl) in the patients and significantly lower than in controls (5.31 +/- 0.53 g/dl). There was, however, no correlation between ionized calcium and albumin. Although measured ionized calcium levels correlated with the total calcium level (r = 0.56) and with estimated ionized calcium levels (r = 0.53), it must be emphasized that severe ionic hypocalcemia may occur despite normal total or calculated ionized calcium levels. Consequently, it is hoped that all hospitals with critically ill patients will soon have this analysis available.