Alternation in traditional vital signs can only be observed during advanced stages of hypovolemia and shortly before the hemodynamic collapse. However, even minimal blood loss induces a decrease in the cardiac preload which translates to a decrease in stroke volume, but these indices are not readily monitored. We aimed to determine whether minor hemodynamic alternations induced by controlled and standardized hypovolemia can be detected by a whole-body bio-impedance technology.
This was a non-randomized controlled trial that enrolled healthy blood donors. Vital signs, as well as shock index and stroke volume (SV), were recorded using noninvasive cardiac system, a noninvasive whole-body impedance-based hemodynamic analysis system, during phlebotomy.
Sixty subjects were included in the study group and 20 in the control group. Blood loss of 450 mL resulted in a significant decrease in systolic blood pressure (5 mm Hg; 95% CI 3, 6) and SV (5.07 mL; 95% CI 3.21, 6.92), and increase in shock index (0.03 bpm/mm Hg; 95% CI 0.01, 0.05). Clinically detectable changes (≥10%) in blood pressure and shock index were detectable in 15% and 5%, respectively. SV decreased by more than 10% in 40% of blood donors. No significant changes occurred in the control group.
Continuous noninvasive monitoring of SV may be superior to conventional indices (e.g., heart rate, blood pressure, or shock index) for early identification of acute blood loss. As an operator-independent and point-of-care technology, the SV whole body bio-impedance measurement may assist in accurate monitoring of potentially bleeding patients and early identification of hemorrhage.