USE OF STROKE DISTANCE IN THE EARLY DETECTION OF SIMULATED BLOOD-LOSS

Objectives: To compare the effects of simulated and mild actual hemorr hage on parameters used traditionally to assess hemorrhaging patients: heart rate (HR), blood pressure (BP), and Shock Index (SI = HR/systol ic BP), with stroke distance (SD) measured ultrasonically as an index of cardiac stroke volume. Materials and Methods: Hemorrhage was simula ted in 19 healthy volunteers by the application of graded lower-body n egative pressure (LBNP) (0, -20, -30, and -60 mm Hg) to pool blood in the lon-er body and reduce venous return, Measurements were also made before and after a standard blood donation (450 mL) in nine healthy vo lunteers, Measurements and Main Results: SD decreased significantly an d progessively from the baseline level of 23.8 +/- 5.7 cm (mean a SD) at each level of LBNP: by 3.4 +/- 1.9, 7.4 +/- 2.5, and 11.8 +/- 3.2 c m at LBNP of -20, -40, and -60 mm Hg respectively. Neither HR nor SI c hanged significantly st the lowest level of LBNP (-20 mm Hg), but they showed progressive, significant increases thereafter. Mean BP did not change significantly at any level of LBNP. Similarly, after a control led hemorrhage of 450 mL, SD decreased significantly by 3.3 +/- 1.6 cm from 22.2 +/- 2.8 cm, whereas HR and SI remained unchanged and mean B P increased slightly. Conclusion: Changes in SD may provide an earlier indication of progressive blood loss than either HR or BP alone or in combination.