Noninvasive evaluation of microcirculatory hemodynamic changes during hemorrhage followed by saline or blood transfusion

The purpose of the study was to examine the ability of a system combining laser Doppler flowmetry (LDF), photoplethysmograph (PPG), and transcutaneous oxygen tension (tc-PO₂) to follow changes in the microcirculation during hemorrhage and following blood or saline return, and to test the hypothesis that such changes precede and might predict changes in the systemic blood pressure. Measurements were performed on the skin of anesthetized rabbits (n = 10) during mild (0-8%), moderate (9-24%), and severe (25-30% of blood volume) hemorrhage, and following complete volume restitution by blood or saline. We found the following: 1) hemorrhage caused typical changes in the LDF, PPG, and tc-PO₂ signals that could be formulated by mathematical models, 2) these signals identified blood as being more efficient than saline for volume restitution following hemorrhage, and 3) microcirculatory changes Precede and might predict systemic hemodynamic events.