Changes in LVOT velocity–time integral during whole blood donation: implications for early detection of hypovolemia in spontaneously breathing patients

Early identification of hypovolemia remains challenging in emergency settings, as vital signs may remain normal during initial blood loss. Point-of-care echocardiography allows assessment of stroke volume through left ventricular outflow tract velocity–time integral (LVOT VTI), but its performance in detecting mild hypovolemia in humans is unclear. To evaluate changes in LVOT VTI following standardized mild blood loss and to assess its ability to identify early hypovolemia in spontaneously breathing adults. In this prospective study, healthy volunteers undergoing whole blood donation (≈ 6–7 mL·kg⁻¹) were assessed using transthoracic echocardiography before donation (T0), immediately after (T1), and 15 min later (T2). The primary outcome was the relative change in LVOT VTI between T0 and T1. Secondary outcomes included the proportion of participants with ≥ 10% reduction in LVOT VTI. Sixty-three participants were analyzed. LVOT VTI decreased by − 11.5% (95% CI, − 15.3 to − 7.7; p < 0.01) between T0 and T1. A ≥ 10% reduction was observed in 50% (95% CI, 37–63) of participants. At T2, VTI remained lower than baseline (− 6.1%; 95% CI, − 10 to − 2.2; p < 0.01). Mild blood loss was associated with early reductions in LVOT VTI. However, the marked inter-individual variability suggests that changes in LVOT VTI alone may not reliably identify mild hypovolemia in individual spontaneously breathing patients. LVOT VTI should therefore be interpreted as one component of the overall clinical and echocardiographic assessment rather than as a standalone marker of hypovolemia. NCT07207629.