Admission ionized calcium levels predict the need for multiple transfusions: a prospective study of 591 critically ill trauma patients.

Background: Deaths from uncontrolled exsanguinating hemorrhage occur rapidly postinjury. Any successful resuscitation strategy must also occur early, underscoring the importance of rapid identification of patients at risk for multiple transfusions. Previous studies have shown low ionized calcium (iCa) levels to be associated with hypotension and function as a predictor of mortality. We hypothesized that admission iCa levels could potentially predict the need for multiple transfusions in critically ill trauma patients.

Methods: Admission iCa was collected prospectively on all trauma activations during a 9-month period. Youden's index was used to determine the appropriate cutpoint for iCa. Outcomes (mortality, multiple transfusions [≥5 units packed red blood cells in 24 hours] and massive transfusion [≥10 units packed red blood cells in 24 hours]) were compared using Wilcoxon rank-sum and χ tests where appropriate. Multivariable logistic regression was performed to determine whether iCa was an independent predictor of multiple transfusions.

Results: A total of 591 patients were identified: 461 (78%) men and 130 (22%) women. Cutpoint was identified as 1.00. iCa was <1.00 (lo-Cal) in 332 patients and≥1.00 (hi-Cal) in 259 patients. Mortality was significantly increased in the lo-Cal group (15.5% vs. 8.7%, p=0.036). In addition, both multiple transfusions (17.1% vs. 7.1%, p=0.005) and massive transfusion (8.2% vs. 2.2%, p=0.017) were significantly increased in the lo-Cal group. Multivariable logistic regression analysis identified iCa<1 as an independent predictor of the need for multiple transfusions after adjusting for age and injury severity (odds ratio=2.294, 95% confidence interval=1.053-4.996).

Conclusions: Low iCa levels at admission were associated with increased mortality as well as an increased need for both multiple transfusions and massive transfusion. In fact, multivariable logistic regression analysis identified low iCa levels as an independent predictor of multiple transfusions. Admission iCa levels may facilitate the rapid identification of patients requiring massive transfusion, allowing for earlier preparation and administration of appropriate blood products.