Limitations of blood supply and walking blood bank implementation in Forward Resuscitative Surgical Detachments during large-scale combat operations: A Monte Carlo simulation model

BACKGROUND: – Hemorrhage remains the leading cause of preventable battlefield mortality. Although early whole blood resuscitation improved outcomes during the Global War on Terror, this relied on permissive operational conditions unlikely to persist in future large-scale combat operations (LSCO). Projected LSCO casualty volumes may rapidly overwhelm current Role 2 Forward Resuscitative Surgical Detachments (FRSDs), and walking blood banks (WBB) may provide only minimal augmentation. This study evaluates blood supply resilience for a Role 2 FRSD across LSCO casualty scenarios and quantifies the incremental benefit of WBB augmentation. METHODS: – A discrete-time, daily-step simulation model was developed in Python to model whole blood dynamics for a Role 2 FRSD over a 30-day conflict. Inventory was tracked using an age-segmented inventory. Baseline stock was 120 units with a resupply of 120 units every 3 days. A 100-donor WBB (56-day deferral) was incorporated. Daily casualties were stochastically generated across escalating intensity, with transfusion demand calculated assuming 20% of casualties required transfusion at 8 units per patient. Primary outcomes included days-to-failure (first unmet unit) and percent demand met over 30 days. RESULTS: – Model-generated aggregate demand closely matched LSCO planning estimates (mean, 30-day demand 10, 075.2 units vs. expected 10, 080). Conventional supply alone failed rapidly once average casualties exceeded 30/day [median, 2 days; interquartile range (IQR), 1–5]. WBB augmentation extended survivability from 30 casualties/day to 11 days (IQR, 7–22) but declined to 5 days (IQR, 2–7) at 40 casualties/day and to 2 days (IQR, 2–4) at 50 casualties/day, with near-immediate failure at higher rates. Demand fulfillment declined sharply as casualty rates increased and was only modestly improved by WBB support. CONCLUSIONS: – Current FRSD blood supply strategies are not sustainable under LSCO casualty conditions. WBBs provide limited surge buffering but cannot replace scalable resupply and forward sustainment in contested environments. (J Trauma Acute Care Surg. 2026;00: 00–00.