Calcium during prehospital trauma blood-product resuscitation: A meta-analysis.

BACKGROUND: Prehospital blood-product resuscitation may be complicated by citrate-related ionized hypocalcemia. Interpretation is limited by nonuniform thresholds and uncertainty about whether the first hospital calcium sample preceded in-hospital treatment. OBJECTIVE: To characterize study-defined hypocalcemia after prehospital blood products and examine its association with prehospital or en-route calcium administration. METHODS: We performed a PROSPERO-registered systematic review and meta-analysis of adult trauma studies reporting prehospital blood products, calcium administration, and ionized‑calcium outcomes. We extracted each threshold, sampling interval, and treatment before sampling. Because only two clinically dissimilar nonrandomized comparative studies were available, study-specific effects were prioritized and pooling was exploratory. Prevalence was examined overall, by threshold category, and with sampling restricted to within 30 min of arrival. RESULTS: Seventeen studies met inclusion criteria. Calcium-exposed patients had lower observed hypocalcemia in the military cohort (risk ratio [RR] 0.40, 95% confidence interval [CI] 0.27-0.61) and civilian air-transport cohort (RR 0.51, 95% CI 0.32-0.82); the exploratory pooled RR was 0.45 (95% CI 0.33-0.61). Across four prevalence studies using thresholds from <1.10 to <1.20 mmol/L, study-specific prevalence ranged from 43.1% to 65.8%. The exploratory pooled prevalence was 60.1% (95% CI 52.0%-67.7%), with threshold-stratified estimates of 53.4% and 65.6%. In two studies with sampling within 30 min, prevalence was 62.9% (95% CI 58.3%-67.3%). CONCLUSIONS: Hypocalcemia was frequently observed after prehospital blood-product resuscitation. Threshold variation, uncertain sampling relative to in-hospital treatment, clinical heterogeneity, and residual confounding preclude causal inference or endorsement of a uniform calcium protocol.