Predictive Value of Ionized Calcium in Critically III Patients: An Analysis of a Large Clinical Database MIMIC II

Background and Objective: ionized calcium (iCa) has been investigated for its association with mortality in intensive care unit (ICU) patients in many studies. However, these studies are small in sample size and the results are conflicting. The present study aimed to establish the association of iCa with mortality by using a large clinical database. Methods: Multiparameter Intelligent Monitoring in Intensive Care II (MIMIC II) database was used for analysis. Patients older than 15 years were eligible, and patients without iCa measured during their ICU stay were excluded. Demographic data and clinical characteristics were extracted and compared between survivors and non-survivors. iCa measure on ICU admission was defined as Ca-0; Ca-max was the maximum iCa during ICU stay; Ca-min was the minimum value of iCa during the ICU stay; Ca-mean was the arithmetic mean iCa during ICU stay. Main results: A total of 15409 ICU admissions satisfied our inclusion criteria and were included in our analysis. The prevalence of hypocalcemia on ICU entry was 62.06%. Ca-0 was significantly lower in non-survivors than in survivors (1.11 +/- 0.14 vs 1.13 +/- 0.10 mmol/l, p<0.001). In multivariate analysis, moderate hypocalcemia in Ca0 was significantly associated with increased risk of death (OR: 1.943; 95% CI: 1.340-2.817), and mild hypercalcemia was associated with lower mortality (OR: 0.553, 95% CI: 0.400-0.767). While moderate and mild hypocalcemia in Ca-mean is associated with increased risk of death (OR: 1.153, 95% CI: 1.006-1.322 and OR: 2.520, 95% CI: 1.485-4.278), hypercalcemia in Ca-mean is not significantly associated with ICU mortality. Conclusion: The relationship between Ca-0 and clinical outcome follows an "U'' shaped curve with the nadir at the normal range, extending slightly to hypercalcemia. Mild hypercalcemia in Ca-0 is protective, whereas moderate and mild hypocalcemia in Ca-mean is associated with increased risk of death.