Do early ionized calcium levels really matter in trauma patients?

Age, injury severity, and base deficit are commonly used prognostic indicators in trauma. This study investigates the relationship between ionized calcium (iCa) levels drawn on arrival to the emergency department, with injury severity, acidosis, hypotension, and mortality.

Adult trauma team activations requiring the highest level of response were identified retrospectively from January 2000 to December 2002. Patients were stratified into two groups: iCa < or = 1 and iCa > 1 mmol/L. The relationship between iCa and injury severity (Trauma Injury Severity Score, Injury Severity Score [ISS], Revised Trauma Scale, Glasgow Coma Scale), age, sampling time, shock (systolic blood pressure [SBP] < 90 at the scene, transport, and admission; base deficit), resource utilization (hospital and intensive care unit length of stay, ventilator days) and mortality was examined. Statistical analysis included chi2 tests, Wilcoxon rank sum tests, p < 0.05 versus iCa > 1, median (25th-75th percentile), and odds ratio (OR).

In all, 396 out of 2,367 patients were identified. Mortality was significantly increased in the iCa < or = 1 group (26.4% versus 16.7%, p < 0.05; OR 1.92). Time to death in iCa < or = 1 was significantly shorter, 0.50 (0-1) versus 1.0 (0-6) days. Mortality was predicted using iCa < or = 1 alone (p < 0.02, OR 3.28), iCa < or = 1 + base deficit (p < 0.02, OR 2.00), and base deficit alone (p = 0.06, OR 1.5). Low iCa was associated with SBP < 90 at the scene and transport (p < 0.01). The incidence of base deficit was higher in the iCa < or = 1 group (p < 0.05).

Low iCa is associated with prehospital hypotension regardless of age, ISS, or sampling time and is a better predictor of mortality than base deficit. Since acidosis reduces calcium binding to serum protein and actually increases iCa, the association between base deficit and iCa in this study requires further investigation.