Interpreting the two-hour partial REBOA safety window: Physiologic context, monitoring limitations, and device-specific considerations.

Recent updates to the Joint Trauma System clinical practice guidelines for resuscitative endovascular balloon occlusion of the aorta incorporate partial aortic occlusion (PAO) for up to two hours in combat casualty care following US Food and Drug Administration 510(k) clearance of the pREBOA-PRO catheter for partial Zone 1 occlusion under defined physiologic parameters. The FDA clearance specifies physiologic targets, including proximal systolic blood pressure of 90 to 110 mm Hg and distal systolic blood pressure >20 mm Hg with pulsatility, indicating that extended occlusion duration is contingent on active titration and physiologic monitoring. These parameters suggest that PAO may be better conceptualized as delivery of a controlled "ischemic dose" determined by both occlusion intensity and duration rather than elapsed time alone. However, real-time ischemic monitoring is limited, distal arterial pressure represents only a surrogate for distal flow, and the relationship between pressure and flow during partial occlusion may vary across catheter designs. This opinion reviews the physiologic basis of PAO, the device-specific context of the two-hour safety window, and the limitations of current monitoring technologies. We also discuss implications for resuscitation strategy and reperfusion planning in austere and prolonged casualty care environments and outline future research priorities.