A direct relationship between ionized calcium and arterial pressure among patients in an intensive care unit.

Serum ionized calcium (Ca+2), creatinine, magnesium, phosphate, and arterial pH were measured in patients on admission to the medical ICU (MICU). Patients were classified into three groups: a) hypotensive (n = 38), those who received vasopressor support for frank hypotension; b) hypertensive (n = 21), those who required vasodilator therapy; and c) normotensive (n = 53), those who required neither vasopressor nor vasodilator therapy. Analysis of variance revealed that only Ca+2, creatinine, and arterial pH differed among the three groups. The difference in Ca+2 persisted when analysis of variance was repeated with creatinine as a covariate. Hypotensive patients had a significantly (p less than .05) lower mean Ca+2 (1.04 +/- 0.13 mmol/L) than normotensive patients (1.13 +/- 0.10 mmol/L), who in turn had a significantly (p less than .05) lower Ca+2 than hypertensive patients (1.18 +/- 0.09 mmol/L). Ca+2 correlated with mean arterial pressure at the time of serum collection (n = 118; r = .43; p less than .01), independent of any other variable. Vasopressor support was required in 41% of hypocalcemic patients in comparison to 14% of normocalcemic patients (p less than .01). Vasodilator therapy was required for 34% of normocalcemic patients, compared to 7.5% of hypocalcemic patients (p less than .01). There appears to be a clinically significant association between hypotension and hypocalcemia. This association may or may not be causal.