Changes in stroke index measured by impedance cardiography in a human model of moderate acute blood loss
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.
Kosowsky
JM
University of Cincinnati, OH.
Collins
SP
Han
J
Gasaway
MD
Storrow
AB