Evidence for a higher risk of hypovolemia-induced hemodynamic instability in females: implications for decision support during prehospital triage.

Lower body negative pressure (LBNP) simulates hemorrhage, and tolerance to LBNP (time to presyncope [TTP]) is indicative of tolerance to blood loss. The purpose of this study was to predict TTP based on demographic characteristics (sex, age, height, and body mass index) and physiological variables (heart rate [HR], systolic arterial pressure, diastolic arterial pressure [DAP], pulse pressure, stroke volume, total peripheral resistance [TPR], and baroreflex sensitivity [BRS]) at baseline, and during 2 levels of LBNP (-15, -30 mm Hg). Multiple linear regression analysis was used to create a model to predict TTP (range: 670 to 2516 seconds, n=187) based on demographic characteristics and physiological variables changes (Δ) from baseline to -30 mm Hg LBNP. The prediction model revealed that TTP (seconds)=1667.5+(5.1×Age)+(61.1×Sex)-(21.5×ΔHR)+(55.3×ΔDAP)-(88.2×ΔTPR)-(4.9×ΔBRS). Most significantly, our analysis demonstrated a lesser survival trajectory for females given the same rate and magnitude of hemorrhage compared to males. Young age and female sex are predictors of low tolerance to blood loss, and should be considered for early triage in the prehospital setting. Reprint &