Changes in stroke index measured by impedance cardiography in a human model of moderate acute blood loss.

Abstract

Early detection of acute hemorrhage is problematic because changes in traditional parameters such as heart rate and blood pressure are notoriously unreliable. OBJECTIVE: To observe the effect of acute, moderate blood loss on stroke index (SI) as measured non-invasively by impedance cardiography. METHODS: Five healthy, adult volunteers were phlebotomized 590 mL over ten minutes. The volume of blood loss was expressed as a percent of estimated total blood volume (TBV) according to the formula TBV = (weight in kg) x (70 mL/kg). Stroke index was measured in a fixed, reclining position before (SI #1) and after (SI #2) phlebotomy, using the BioZ.com (Cardiodynamics International Corporation, San Diego, CA) thoracic bioimpedance monitor. Absolute and relative changes were calculated. RESULTS: In each volunteer, a fall in SI was noted after phlebotomy. The percent change in SI ranged from 8% to 18% (table 15-1). There appeared to be a correlation between blood loss as a percent of estimated total blood volume and the percent decline in SI among these volunteers. CONCLUSIONS: Impedance cardiography reliably detected moderate acute blood loss in this small set of healthy, adult volunteers. If these results can be quantified and validated prospectively in a larger population, SI may prove to be a valuable, non-invasive parameter for detection of early hemorrhage shock.